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POTASSIUM REQUIREMENT AND POTASSIUM BIOAVAILABILITY
IN THE YOUNG PIG

BY

Nadine Rae Combs

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Animal Science

1984

ABSTRACT
POTASSIUM REQUIREMENT AND POTASSIUM BIOAVAILABILITY IN THE
YOUNG PIG
BY

Nadine Rae Combs

The potassium requirement was estimated in four trials,
using least squares analysis of a linear plateau response
for gain. The four estimates obtained were 0.30, 0.33, 0.26
and 0.18% potassium in the diet. These estimates were not
inconsistent with published values.

Hematological and urinary responses were measured
during five trials to identify criteria that were linearly
related to dietary potassium level for use in a
bioavailability assay. For the responses measured, a
bioavailability assay using urinary potassium excretion as
the primary response variable seemed the most promising.

Using daily potassium retention data, the relative
bioavailability of potassium was estimated. Potassium
retention was approximately 90% on all diets containing
potassium acetate as the primary potassium source. Using
potassium acetate as the standard (100%), potassium
bioavailability was 103% for potassium carbonate, 106% for
potassium bicarbonate, 90-95% for corn and 97% for

solvent-excreted soybean meal.

ACKNOWLEDGEMENTS

Upon completion of this phase of my education, I would
like to dedicate this thesis to those people whose support
and assistance made it possible. Dr. Elwyn R. Miller,
serving as my major professor, provided me with the
opportunity to explore my field and gain valuable experience
in many auxilary areas as well. The members of my gradute
committee, Drs. Miller, Maynard G. Hogberg, Duane E. Ullrey
and John L. Gill, challenged me to look at the field and, in
particular my Master's research, for the things that would
give me a personal sense of accomplishment as well as
contribute to the field in general. The host of new friends
and acquaintances here at MSU, including my fellow graduate
students, have done their best to keep me on an even keel,
providing hours of their time to assist me with my research
and serve as sounding boards for my ideas. Dr. Pao Kwen Ku
and Mrs. Phyllis Whetter provided hours of assistance in the
laboratory and helped to keep my work in perspective. My
Judy Witwer, whose professional preparation of this
manuscript speaks for itself, has helped me meet many
deadlines and obligations over the last two years as a
secretary and a friend. The special friends over the years,
especially Ms. Pat McGee, Mrs. Eleanor Weirauch and the
late Lyal Weirauch, maintained their faith in, and support

of me in order to get me through some rough times and give

me the determination to see my education through to the end.
Above all, this manuscript must be dedicated to my parents,
Mr. and Mrs. Norval Combs, and my family. They have endured
a number of changes in and challenges from their
"professional student" and have added a unique perspective
to my work. Their patience and continued support of me has
served as a source of inspiration to me in completing this

work.

TABLE OF CONTENTS

INTRODUCTIOTJ O O O O O O O O O O O O O O O O O O 0

REVIEW OF LITERATURE O O C O O O O O O O O O O O O

I.

II.

III.

The Physiology of Potassium . . . . . . . .
A. The Early History of Potassium. . . . .
B. Distribution of Potassium . . . . . . .
C. Functions of Potassium. . . . . . . . .
D. Potassium Homeostasis . . . . . . . . .
E. Potassium Deficiency. . . . . . . . . .
F. Potassium Toxicity. . . . . . . . . . .
G. Variation of Potassium Content among
Feedstuffs. . . . . . . . . . . . . . .

Potassium Requirement of the Pig. . . . . .
A. Factors Affecting Potassium Requirement
Other Species . . . . . . . . . . . . .
B. Evaluation of the Potassium Requirement
the Young Pig . . . . . . . . . . . . .

Bioavailability of Potassium from Various
Sources . . . . . . . . . . . . . . . . . .
A. Methods of Determining the Bioavailabil
of Minerals . . . . . . . . . . . . . .
B. Bioavailability of Potassium in Natural
Feedstuffs and Supplemental Potassium
Sources . . . . . . . . . . . . . . . .

MATERIALS AND METHODS. O O O C O O O 0 O O O O O O

I.

II.

Potassium Requirement Trials. . . . . . . .
A. Trials 1 and 2. . . . . . . . . . . . .
8. Trial 3 . . . . . . . . . . . . . . . .
C. Trials 4 and 5. . . . . . . . . . . . .

Bioavailability Trials. 0 O O O O O O O O 0

RESULTS AND DISCUSSION . . . . . . . . . . . . . .

I.

II.

Potassium Requirement Trials. . . . . . . .
A. Estimates of Requirement from Gain Data
B. Determination of Linear Response to

Treatment of Other Variables. . . . . .
C. Conclusions in Regard to the
Bioavailability Studies . . . . . . . .

Potassium Bioavailability Trials. . . . . .
A. Potassium Bioavailability in Potassium
Carbonate (K2C03) . . . . . . . . . . .
B. Potassium Bioavailability in Potassium
Bicarbonate (KHCOZ) . . . . . . . . . .

C. Potassium Bioavailability in Corn . . .
D. Potassium Bioavailability in Solvent-
extracted Soybean Meal. . . . . . . . .

i

Page

H

(AMI-J
l—‘U'IU'IQUJNNN

32

36

36

38

44

44

54
59
59
59
64
67
73
83
83
83
9O
92
96
96

97
100

105

CONCLUSIONS. . . .

LIST OF REFERENCES

ii

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

10.

11.

12.

14.

15.

16.

17.

LIST OF TABLES

Body Mineral Concentration of Animals (Live
Wt. Basis, Average Values). . . . . . . . .

Distribution of Potassium . . . . . . . . .
Enzyme Systems Activated by Potassium . . .

Potassium Intake (grams), Throughput at 4

Re-entrant Cannula Sites and Fecal Excretion

Calculated for 40 kg Pig Receiving 1.7 kg
Diet Per Day. 0 O O O O O O O O O O O O O 0

Effect of Varying K+ and Cl' on Average
Daily Performance in Young Pigs . . . . . .

Potassium Content in Feedstuffs (% K) . . .

Potassium Content of Feedstuffs Commonly
Used in Livestock Rations . . . . . . . . .

Effect of Potassium Level Upon Pig
Performance: Results of EXperiment l,
Jensen et al (1961) . . . . . . . . . . . .
Effect of Potassium Level Upon Pig
Performance: Results of Experiment 2,
Jensen et a1 (1961) . . . . . . . . . . . .

Analysis of Cereal Grain Fractions for
Potassium . . . . . . . . . . . . . . . . .

Bioavailability of Potassium from Various
Sources for Poultry, Swine and Ruminants. .

Basal Diet Used in Trials 1 and 2 . . . . .

Composition of Vitamin Mix Used in Purified
Basal Diets O O O O O O O O O O O O O O O 0

Composition of Mineral Mix Used in Purified
Basal Diets . . . . . . . . . . . . . . . .

Modified Basal Diet Used in Trial 3 . . . .
Semipurified Diet Used in Trials 4 and 5. .

Vitamin-Trace Mineral Premix Used in
Semipurified Diets. . . . . . . . . . . . .

iii

ll

17

26

33

34

4O

42

57

58

61

62

63

65

68

69

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

18.

19.

20.

21.

22.

23.

24.

25.
26.
27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

39.

Depletion Phase Diets Used in Trials 6, 7,
8 and 9 O . . . . I . . 0 O O . O O O O O 0

Calculated Nutrient Analysis of Depletion

Phase Diets . . . . . . . . . . . . . . . .
Experimental Diets Used in Trial 6 . . . .
Experimental Diets Used in Trial 7 . . . .

Experimental Diets Used in Trial 8 . . . .

Experimental Diets Used in Trial 9 . . . .
Average Daily Gain of Pigs in Trial 1 . . .
Average Daily Gain of Pigs in Trial 2 . . .
Average Daily Gain of Pigs in Trial 3 . . .

Average Weekly Gain of Pigs in Trial 4. . .

Response of Plasma K and Na to Dietary
Levels of K in Trial 1. . . . . . . . . . .

Response of Plasma K and Na to Dietary
Levels of K in Trial 2. . . . . . . . . . .

Hematology and Urinary Responses to Levels
of Dietary K in Trial 3 . . . . . . . . . .

Urinary Potassium Responses to Levels of
Dietary K in Trial 5. . . . . . . . . . . .

Results of the Potassium Carbonate Trial
(Trial 6) . . O O O . . . O O O . . O O . 0

Relative Bioavailability of Potassium in
Potassium Carbonate . . . . . . . . . . . .

Results of the Potassium Bicarbonate Trial
(Trial 7) . . . . O . . . O O . . O O O O 0

Relative Bioavailability of Potassium in
Potassium Bicarbonate . . . . . . . . . . .

Results of the Corn Trial (Trial 8) . . . .

Relative Bioavailability of Potassium in
corn. . O O . . . O . . I O O O O . . O O 0

Results of the Soybean Meal Trial (Trial 9)

Relative Bioavailability of Potassium in
Soybean Meal. . . . . . . . . . . . . . . .

iv

Page

74

75
77
78
79
80
84

86
87

88

91

91

93

94

98

99

101

102

103

108

109

LIST OF FIGURES

Figure 1. Composition of Body Fluids. . . . . . . .

Figure 2. Influx and Efflux of Potassium along the
GI TraCt. . . O . . O . I . . . . O O O 0

Figure 3. Effect of Extracellular Potassium Ion
Concentration Changes on Extracellular
Fluid Aldosterone Concentration . . . . .

Figure 4. Effect of Increasing Potassium Intake on
Plasma Potassium Concentration in the
Presence or Absence of the Aldosterone
Feedback System . . . . . . . . . . . . .

Figure 5. Estimate of K Requirement in Trial 1 . .

Figure
Figure

Figure

6.

7.

8.

Estimate
Estimate

Estimate

of K Requirement
of K Requirement

of K Requirement

in
in

in

Trial 2
Trial 3

Trial 4

86

87

88

INTRODUCTION
Potassium has long been recognized as a dietary
essential for man and animals (Linsner, 1930). Requirement
values for most species, including swine, were established
in the first half of this century (Hughes and Ittner, 1942;

Meyer et al., 1950; Potassium In Animal Nutrition, 1981;

 

 

Linsner, 1980). Due to the substantial content of potassium

of many natural feedstuffs (Linser, I980; Potassium In

 

Animal Nutrition, 1981; Miller and Kornegay, 1983),

 

potassium assumed the status of an essential, but
non-critical, element until recent years (Linser, 1980).
The last two decades have seen many changes in the swine
industry that have necessitated re—evaluation of many
nutrient requirements and interactions, including those of
potassium (Miller and Kornegay, 1983). In the last five
years alone, many research stations have been investigating
the possible interaction of potassium and lysine in swine
(Austic, 1983; Austic et al, 1983; Austic and Calvert, I981;
Froseth et al, 1982; Mabuduike et al., 1980; Miller et al.,
1982; Walstrom et al, 1983: Zimmerman, 1982). The results
of this research are inconsistent. This inconsistency may
be due to several factors, including among others,
electrolyte balance in the diets, interaction of potassium
with nutrients other than lysine, accumulation of basic
amino acids intracellularly and the bioavailability of

potassium. This study was undertaken to evaluate the

2
relative bioavailability of potassium in four selected feed
ingredients. This required that the comparisons be made at
a range of levels less than that of the requirement of the
young pig and on the basis of measures that are very
sensitive to changes in potassium status within that range.
Therefore, the potassium requirement of the young pig was
also reevaluated in order to verify the requirement and
identify those measures sensitive enough to undertake the

bioavailability work.

REVIEW OF LITERATURE
I. The Physiology of Potassium
A. The Early History of Potassium
Potassium is a member of a chemical group called alkali
metals. Other metals in this group include sodium, lithium,
rubidium, cesium and francium. Metals of this group are
among the most reactive minerals and are not found naturally

in the uncombined state (Linsner, 1980; Potassium In Animal

 

Nutrition, 1981). Chemically, potassium is very much like

 

sodium and the two are found in close association in many
reactions in biological systems (Linsner, 1980: Moose, 1966;

Potassium In Animal Nutrition, 1981).

 

 

The chemical symbol for potassium is K, after the Latin
word for this metal, Kalium. Potassium has an atomic weight
of 39.102 and was first isolated in its elemental form by

Sir Humphrey Davy in 1807 (Potassium in Animal Nutrition,

 

 

1981). Sidney Ringer, in 1883, is credited with first

recognizing the importance of potassium in animal tissues,

3
in connection with his perfusion studies with frog hearts.
Many experiments in the early and middle nineteenth century
have also been cited to demonstrate the essential nature of

potassium in the diets of animals (Linsner, 1980; Potassium

 

In Animal Nutrition, 1981). Since that time, a great deal

 

of information on physiological function and distribution in
the body has accumulated. Until the last 25 years, however,
little emphasis has been placed on the nutritional

investigations of potassium (Linsner, 1980; Potassium In

 

Animal Nutrition, 1981; Miller and Kornegay, 1983).

 

B. Distribution of Potassium
Potassium is the third most abundant mineral element in
animal tissue, exceeded only by calcium and phosphorus

(Linsner, 1980: Moose, 1966; Potassium In Animal Nutrition,

 

 

1981). Average values of the mineral content of animals are
given in Table I. Expressed in terms of metabolically
active elements, potassium is the most abundant element,
since a greater percentage of potassium is present in the
body in a rapidly exchangeable form (Crenshaw, 1983).
Potassium is found in every cell in the body, therefore
the highest proportion is in the body parts that have the
most cells. Over two-thirds of the body potassium is found
in the muscle and skin (Linsner, 1980; Moose, 1966). The
average distribution of potassium in the body is shown in

Table 2. A dressed carcass will contain about 75% of the

4
Table 1. Body Mineral Concentration of Animals (Live Wt.

Basis, Average Values)a

 

 

Major Elements % Minor Elements ,ppm
Calcium 1.0-2.0 Iron 80
Phosphorus 0.7—1.2 Zinc 30
Potassium 0.3 Copper 3
Sulfur 0.25 Iodine 0.4
Sodium 0.15 Manganese 0.3
Chlorine 0.15 Cobalt 0.2
Magnesium 0.045
Chromium +
Molybdenum +
Selenium +
Fluorine +
Nickel +

 

3Adapted from Potassium In Animal Nutrition (1981).

 

 

5

Table 2. Distribution of Potassiuma

 

Potassium Content as

 

Tissue or Organ % of Total Body Potassium
Muscle 56.0
Skin 11.1
Digestive Tract 5.6
Liver 5.3
Red Blood Cells 4.2
Blood Plasma 2.2
Brain 1.4
Kidney 0.9
Lung 0.5
Spleen 0.4
Heart 0.4
Bones and other groups 12.0

 

aTaken from Linsner (1980).

6
potassium in the animal body (Linsner, 1980) with every 100
pounds of carcass containing approximately one-third pound
of potassium (Moose, 1966).
Potassium exists in these tissues as the principal
intracellular cation, in contrast to sodium, which plays a
similar role extracellularly (Combs, 1981: Linsner, 1980:

Potassium In Animal Nutrition, 1981: Miller et al., 1982).

 

 

As such, 89% of the body potassium is located within the
cell (Combs, 1981). The marked segregation of potassium and
sodium, as well as the distribution of other electrolytes,
in the body fluids is illustrated in Figure 1. Composition
of intracellular fluids vary, depending on the nature and

function of the cell (Linsner, 1980; Potassium In Animal

 

Nutrition, 1981).

 

At birth, total body sodium content is equal or
slightly greater than the potassium content. The sodium
content decreases with age, while the potassium content
increases in proportion to the accretion of body protein.

At chemical maturity of the animal, the potassium content is

approximately twice that of sodium.

C. Functions of Potassium

Potassium is associated with sodium and other
electrolytes in a number of biological phenomena. These
include osmotic balance, acid-base balance, neuromuscular

function and water balance. In the body, potassium salts

Figure l.

160

140

120

100

Inqu L

60

40

20

 

 

 

 

 

 

 

 

 

 

 

 

Composition of Body Fluidsa

 

 

 

 

 

 

 

 

 

aTaken from Combs (1981).

_. Non_ H.Hcog
__ Electrolytes _ HCO‘
H.Hco3 » 3
__ HC03
.. HPO4
4— K+
"' Na+
__ c1'
b O
— ——/”"94
. ~50;
7' ..___.w-r_.;g,. ‘Org . acids
— 1“ 53F???
BLOOD CELL
PLASMA FLUID

8

dissociate to yield potassium as a free cation or positively
charged electrolyte that must be balanced by an anion or
negatively charged electrolyte (Crenshaw, 1983). Sodium,
potassium and chloride are the three major electrolytes,
along with less substantial amounts of calcium, magnesium,
phosphorus and sulfur, that determine the cation-anion
balance (Austic, 1983; Crenshaw, I983; Linsner, 1980).

Potassium is the main factor in cellular osmotic
balance, contributing 50% of the osmolarity of intracellular
fluid, while sodium and chloride contribute 80% of the
extracellular osmolarity (Crenshaw, 1983). Cellular
osmolarity is the concentration of molecules, irrespective
of charge, within a semipermeable membrane. Diffusion of
water occurs to maintain an equilibrium on either side of
the membrane. Regulation of cation-anion concentration to
maintain osmotic balance predominates over the mechanisms
involved in regulation of acid-base balance (Crenshaw,
1983). Regulation of osmotic balance is accomplished by
means of hypothalamic osmoreceptors that respond primarily
to sodium levels, with no response to potassium levels and
only slight response to changes in urea or glucose
concentrations (Guyton, 1977). Thus, serum sodium level
plays the major role in maintenance of osmotic balance,
being regulated to maintain both extracellular and
intracellular osmolarity (Crenshaw, 1983).

Maintenance of osmotic balance, although predominant in

9
regulation, is no more integral to cell survival than the
maintenance of acid-base balance. In studies reported by
Austic (1983), it appears that monovalent electrolytes have
a greater impact on acid-base balance than the divalent
electrolytes, although the reason for this is not clear.
Monovalent electrolytes are cleared primarily by the kidney
whereas divalent electrolytes are regulated muCh more
through the absorptive process of digestion. Those cleared
in the kidney may impact more directly on acid-base balance
as the kidney has a regulatory role in maintenance of body
fluid pH. Regulation of acid-base balance refers to
regulation of the hydrogen ion concentration. The potassium
and hydrogen ion concentration in the extracellular fluid
parallel each other, in part because of the effects of the
potassium on renal hydrogen ion secretion (Ganong, 1979).
Much of the filtered K+ is removed from the tubular fluid
by active reabsorption in the proximal tubules of the kidney
and K+ is then secreted into the fluid by the distal
tubular cells. Normally, the amount secreted is
approximately equal to K+ intake and this K+ balance is
maintained. Sodium ions are generally reabsorbed in the
distal tubules, where potassium ions are secreted, in
association with H+ secretion. Sodium migration
intracellularly also tends to lower the potential difference
across the tubular cell, favoring movement of K+ into the

tubular lumen. Therefore, there is competiton for Na+ in

10
the distal tubular fluid. Potassium ion excretion is
decreased when Na+ reaching the distal tubule is low and
is also decreased when H+ secretion is increased. When
total body K+ is high, H+ secretion is inhibited,
apparently due to an intracellular alkalosis, facilitating
K+ secretion and excretion, promoting an extracellular
acidosis. Conversely, an intracellular acidosis exists
during K+ depletion, decreasing K+ secretion and
promoting H+ secretion into the urine. Hydrogen ions are I
removed from the body and HCO3 reabsorption is increased,
producing an extracellular alkalosis (Ganong, 1979). In
acid-base equilibrium, potassium also serves as an available
base to neutralize organic acids (Moose, 1967; Midwestern

Potash News Letter, 1962; Linsner, 1980: Potassium In Animal

 

Nutrition, 1981).

 

Potassium also serves as a cofactor in many enzyme
systems. Many of the enzymes have a specific requirement
for potassium while in other cases potassium may act with
other ions, such as Na+, Mg++ and Ca++, in
influencing enzyme activities (Linsner, 1980). Among the
processes on which potassium exerts an effect, its enzymatic
systems include those involved in phosphate metabolism,

C02 metabolism, amino acid synthesis and carbohydrate
metabolism. Table 3 contains a list of some of the enzymes
whose activity is activated or stimulated by potassium

(Midwestern Potash Newsletter, 1962; Moose, 1967; Linsner,

Table 3.

11

Enzyme Systems Activated by Potassiuma

 

Enzyme

Function

 

Adenosine triphosphatase
(ATPase)

Adenylic phosphorylase

Pyruvate Kinase

Glutaminase II

Phosphotransacetylase

Hexokinase

Fructokinase

Cholinesterase

Pantothenate synthetase

Glutathione synthetase

Formylase (Kynurenine
formamidase)

Hydrolyzes phosphate from
energy-rich ATP and releases
energy. ATP is one of the major
energy storage compounds in
tissue.

Necessary to add phosphoryl
groups to adenylic acid or
adenosine compounds.

Catalyzes transphosphorylation of
phosphoenol pyruvate to ADP to
form pyruvate and ATP. Pyruvate
is used in the acetylation of
Coenzyme A.

Deamination of glutamine in the
formation of diphosphopyridine
nucleotide which is important in
biological oxidation reactions.

Involved in the transfer of
acetyl groups to acceptors: i.e.
the formation of acetyl coenzyme
A which, in the presence of
choline, forms acetylcholine.

Aids in formation of
phosphorylated sugar derivatives
in carbohydrate metabolism.

Necessary for the addition of
phosphoryl groups to fructose in
the formation of
fructose-l-phosphate in
carbohydrate metabolism in the
liver.

Inactivates muscle stimulation by
hydrolyzing acetylcholine to
choline and acetic acid

Necessary for formation of
pantothenate, an essential
portion of Coenzyme A.

Necessary for the formation of
glutathione (GSH), required for
many cellular oxidation-reduction
systems.

Involved in tryptophan metabolism
in the liver, possibly
influencing the tryptophan level
of the blood.

Table 3 (Cont'd)

l2

 

Enzyme

Function

 

Salivary and pancreatic
amylases

Lactase or galactosidase

Carbonic anhydrase

Serine dehydrase

Homoserine dehydrase

Threonine dehydrase

Act to break down starch and
glycogen.

Required for cleavage of lactose
and other glycosidic bonds,
hydrolyzing certain
polysaccharides to simple sugars
in carbohydrate metabolism.

A decarboxylating enzyme which
acts on bicarbonate, yielding
C02 and water as end products.

Necessary for the formation of
cystathionine in amino acid
metabolism.

Required for the formation of
cysteine, a sulfur-bearing amino
acid.

Necessary for the deamination of
threonine.

 

3Adapted from Potassium In Animal Nutrition (1981) and
Midwestern Potash News Letter (1962).

 

 

13

1980: Potassium In Animal Nutrition, 1981).

 

 

The intracellular-extracellular separation of sodium
and potassium is responsible in large part for generating
membrane currents required for neuromuscular function. This
separation is maintained by means of an energy—requiring
sodium pump, at the expense of ATP. This energy demanding
process accounts for a large percentage of the animal's
energy expenditure in the basal state (Ganong, 1979;

Linsner, 1980; Potassium In Animal Nutrition, 1981). The

 

 

sodium pump functions to actively transport sodium out of
the cell, against its chemical and electrical gradients and
to allow potassium to enter the cell by simple diffusion

(Linsner, I980: Potassium In Animal Nutrition, 1981). When

 

 

a nerve cell is stimulated, sodium ions move into the cell
and potassium ions move out, establishing bioelectric
impulses. Muscle activity is also accompanied by an
exchange of sodium and potassium across muscle cell
membranes. As much as 30% of the cellular potassium can be

lost in exhaustive exercise (Linsner, 1980; Potassium In

 

Animal Nutrition, 1981). Adequate potassium is required for

 

normal cardiac activity. Jensen et al. (1961) reported that
pigs, on a potassium-deficient diet, demonstrated abnormal
cardiac activity as shown by electrocardiograms (ECG) after
being on test for 28 days. They found this to be in
agreement with previous reports for the calf and the chick.

Cardiac function requires a proper balance of calcium and

l4
potassium for the rhythmicity of contractions. Excess
calcium, or normal levels of calcium in the absence of
potassium, lengthens the systole (contraction) of the heart
at the expense of diastole. This leads to the heart finally
stOpping in a fully contracted state called calcium rigor.
The reverse occurs when potassium is in excess or unbalanced
by calcium. More of the cardiac cycle is occupied by rest
periods between beats and the heart finally stops in a
completely relaxed state called potassium inhibition

(Linsner, 1980; Potassium In Animal Nutrition, 1981, Miller

 

 

et al. 1982).
Potassium has been shown to affect amino acid uptake in

many species (Potassium In Animal Nutrition, 1981). Frost

 

 

et a1. (1953) found that protein depleted rats, even when
offered a complete source of amino acids when potassium was
withheld, did not recover. Rinehart et a1. (1967) found
that chicks fed a potassium-deficient diet incorporated
significantly less radiolabeled leucine, used to index rate
of protein synthesis, than did chicks receiving adequate
potassium. Research cited earlier on the interaction of
potassium‘and the basic amino acids in swine suggest that
there is evidence of potassium effect on amino acid uptake
in swine also.

Potassium has also been associated with bone
calcification in some species. Gillis (1950), in studies

with both chicks and rats, found that the potassium

15
requirement was increased when phosphorus content of the
diet was suboptimal. He also found that bone calcification,
measured by the per cent of bone ash, was reduced when the
animals received diets containing inadequate potassium,
probably due to a disturbance in phosphorus metabolism.
Austic (1983) reviewed a number of studies in rats and
chicks where electrolyte balance (Na + K - Cl) has been

implicated in bone and cartilage abnormalities.

D. Potassium Homeostasis

Potassium homeostatic mechanisms are intimately
involved in the functional processes in which potassium
plays a role. No single organ plays a more important role
in the homeostasis of potassium than the kidney. The body
content of potassium is regulated by alteration of serum
potassium concentration. Potassium excretion is regulated
by epithelia in distal portions of the nephron and large
intestine. Sodium-potassium-ATPase pumps, located in the
basolateral cell membrane are responsible for moving
potassium (Hayslett and Binder, 1982; Crenshaw, 1983).
Potassium excretion in the renal tubular system is
influenced by extracellular potassium levels,
mineralcorticoids, acid-base balance, flow rate of luminal
fluid, sodium concentration and anion composition of luminal
fluid. In the colon, potassium excretion is affected by

mineralcorticoids, glucocorticoids, sodium concentrations

l6
and extracellular potassium concentrations (Crenshaw, 1983).
The amount of potassium excreted by the kidney or colon can
also be affected by the type of diet fed. Partridge
(1978a), using 17 pigs with re-entrant cannulas in the
duodenum, jejunum or terminal ileum and 24 non-cannulated
pigs in a conventional digestibility trial, measured the
effects of three different diets on mineral passage and
excretion. The values were then used to calculate the
direction and net movement of the elements through the
mucosa of four parts of the digestive tract anterior to the
collection sites. Three diverse diets were used: barley,
wheat and fishmeal (BWF); starch, sucrose and groundnut meal
(SSG); and starch, sucrose and casein (SSC). Measurements
were made for calcium, phosphorus, magnesium, sodium and
potassium. The intake and throughput of potassium at the
various sites is presented in Table 4. Partridge found that
there was a significant net absorption of potassium between
the duodenum and mid-jejunum on all three diets (P<0.05).
The principal region of potassium absorption, however, was
the major portion of the small intestine from the
mid-jejunum to the terminal ileum (P<0.01) for all three
diets. Further net absorption of potassium occurred in the
large intestine with the two purified diets (SSG and SSC)
but was not evident on the cereal-based diet (BWF). Reduced
apparent absorption of potassium, posterior to the terminal

ileum, in the presence of high-cellulose content in the diet

17

Table 4. Potassium Intake (grams), Throughput at 4

Re-entrant Cannula Sites and Fecal Excretion Calculated

for 40 kg Pig Receiving 1.7 kg Diet Per Daya

 

 

 

 

Dietb

BWF SSG SSC

Intake 11.47 12.72 4.28
Cannula Sites

Duodenum 14.58 14.25 6.88

Jejunum 9.86 9.67 4.23

Ileum 3.44 3.31 0.65

Fecal Excretion 3.90 1.91 0.21

 

 

aAdapted from Partridge, 1978a.

bDefinition of diets:

BWF = barley, wheat and fishmeal (6.719 K/kg diet).

SSG

SSC = starch, sucrose and casein (2.459 K/kg diet).

starch, sucrose and groundnut (7.459 K/kg diet).

18
has been observed by Partridge (1978b), probably due to both
the cation—binding capacity of cellulose and increased
passage rate associated with increased fiber diets.

In a series of studies on factors affecting mineral
utilization in baby pigs, Hendricks (1967) measured
absorption and secretion of minerals along the GI tract of
pigs receiving casein or soy diets at two different levels
of protein intake. Using a chromic oxide ratio technique,
Hendricks found that casein in the diet, regardless of
level, resulted in an increased influx of potassium into the
cranial small intestine and a compensatory efflux of
minerals from the caudal small intestine. The influx of all
minerals, via pancreatic and biliary secretions, masked any
absorption from the cranial small intestine, while net
absorption of potassium occurred in all other portions of
the GI tract. Figure 2 presents Hendricks' findings in
relation to the movement of potassium along the GI tract.

Movement of potassium across the gastrointestinal
mucosa is thought to be primarily due to diffusion (Ganong,
1979). The net movement of potassium is proportional to the
potential difference between the blood and the intestinal
lumen. These potential differences result in rather
substantial concentrations of potassium, on the basis of
diffusion alone, in the jejunum, ileum and colon. Loss of
ileal or colonic fluids in chronic diarrhea can lead to

severe hypokalemia due to the high concentrations of

19

Figure 2. Influx and Efflux of Potassium Along the GI

Tracta.

MOVEMENT IN GJ. YIACT OF BABY PIGS

 

I 2 3 4 5 6
ABSOIIED
D.M. D.M. BM. Na Mg
P Co Cu K Na
P

   

SECRETED

Zn ' In
C" ’ Co
C0 C0
Mn Mn
N

   

stomach.

 

cran.s.i._ .,_

caud.s.i.. '

cecum.-- ‘ ._

colon.-.§ ' ' '

rectum?

“I. 20 40 so so
— casein I D Emma]. soy
"“3270. "“3270

aTaken from Hendricks (1967).

   
 
  
  
 

20

potassium contained in these fluids (Ganong, 1979).

Regulation of serum potassium level does not appear to
be controlled as rigidly as serum sodium level. Potassium
excretion in the urine is regulated primarily in the distal
tubulars of the kidney by the hormone aldosterone (Crenshaw,
1983). Approximately 65% of the potassium in the glomerular
fluid is absorbed in the proximal tubules and another 25% is
absorbed in the loops of Henle; therefore, only about 10% of
the original glomerular filtrate content is delivered to the
distal tubular system. Potassium is transported from the
peritubular fluid to the distal tubular epithelial cells at
the same time as sodium is transported in the opposite
direction (Guyton, 1977). Potassium then diffuses from the
cells into the tubular lumen due to its high concentration
within the epithelial cell. This secretory transport of
potassium to the distal tubules is necessary to eliminate
potassium from the extracellular fluid in order to control
serum potassium. This secretory mechanism is controlled by
the effects of aldosterone on the distal tubular system.
The aldosterone negative feedback system, responsible for
promoting potassium secretion when extracellular potassium
rises, is stimulated by high extracellular potassium. The
effect of increasing potassium on circulating aldosterone
levels is illustrated in Figure 3. Very small changes in
potassium concentration bring about rather substantial

changes in aldosterone concentration. The increase in

21
Figure 3. Effect of Extracellular Potassium Ion
Concentration Changes on Extracellular Fluid

Aldosterone Concentrationa

70-
2!
Q
P-
3‘: so-
P-
2!
UJ .
9 so-
0 O
3.:

a 40-
% ‘5.
5 e
550 30~
o 9
C3
-1 E.
4 c 20"
<
2
2 IO-
.J
O.

 

 

 

3.0 3'5 4T0 41.5 5.0 5.5 6.0 61.5
SERUM POTASSIUM CONCENTRATION mEq./liter

aTaken from Guyton, 1977.

22
potassium excretion by the kidneys reduces extracellular
fluid potassium concentration back toward normal. In the
absence of the aldosterone system, increasing potassium
intake results in increased circulating potassium ion
concentration (Figure 4). This can lead to cardiac
arrhythmias and death can result from the hyperkalemic
condition. Conversely, hypokalemia due to hyper-aldosterone
secretion can result in severe muscle weakness or even
paralysis as nerve and muscle fiber membranes become
hyperpolarized (Guyton, 1977).

A large percentage of the control over potassium
excretion is exerted through the osmotic and acid—base
balance systems discussed earlier. Therefore, factors that
affect maintenance of the balance in either system also
affect potassium balance. In particular, the buffer
systems, used by the body to maintain acid-base balance by
tying up excess hydrogen ions, can affect potassium balance
since excretion of potassium is affected by the level of the
hydrogen ions. Potassium can also function as a cation for
binding the monobasic phosphate ion produced in one of the
buffering systems (Crenshaw, 1983). Another buffering
system, utilizing ammonia produced by catabolism of
glutamine in the kidney and under control of the hydrogen
ion concentration there, has been reported to be influenced

by the potassium—status in rats (Crenshaw, 1983).

23
Figure 4. Effect of Increasing Potassium Intake on Plasma

Potassium Concentration in the Presence or Absence of

the Aldosterone Feedback Systema.

4.8-1
6 /
E 46- /
o: 5 /
I— /
UZJ /
0 4.4- /
Z /
8... - //
2“? M.
2 =4.2- /
(n g. . /
m m /
4 Aldosterone
I— E
0V / system
0- 4-0‘ // blocked
; /
(n //
S 3.3- .
a.

 

 

0 3b 6T0 Sb I2'O |50 I80 2IO
POTASSIUM INTAKE (mEq/doy)

aAdapted from Guyton, 1977.

24

The level and source of ions can also affect potassium
balance. Chloride deficiencies have been reported to result
in metabolic alkalosis as have potassium deficiencies in
animals receiving minimum sodium. This latter effect
resulted from increased bicarbonate ions, due to low sodium,
and the need for a cation, in this case potassium, to
maintain electroneutrality (Crenshaw, 1983). Sodium can
also replace potassium intracellularly during a potassium
deficiency, as can basic amino acids (Miller et al, 1982).
The source of anions can also affect the excretion of
cations such as potassium. Anions such as chloride are
readily reabsorbed by the kidney, while anions such as
sulfate, nitrate and even phosphate at high serum
concentrations are not reabsorbed as readily by the kidney.
Therefore, the latter ions require either sodium, hydrogen,
potassium, ammonium or another cation for excretion,'
depending on which cation is available.

Grunert et al. (1950) and Burns et al. (1953) have
reported the existence of an interrelationship between
dietary sodium and potassium in rats and chicks,
respectively. Combs (1981) investigated the
interrelationships of sodium, potassium and chloride in 160
pigs weaned at three weeks of age. He used a 3 X 3
factorial design with potassium levels of .3, .6 and .9%
with chloride levels of .07, .13 or .18%. Sodium levels

were held constant at .l3%. Eighteen pigs were placed on

 

 

25
each of the nine dietary treatments. Combs reported rate of
gain was significantly affected by level of potassium While
feed efficiency was not significantly affected by either
level of potassium or chloride (Table 5). He observed a
growth depression at the high level of potassium. Serum
electrolytes (Na, K, Cl, Ca, P) were found to be
significantly affected by chloride level, while the serum
enzymes, alkaline phosphatase, lactic dehydrogenase (LDH)
and serum glutamicoxaloacetic transaminase (SGOT), were
higher at the lowest potassium level (P<0.05), but of
unknown physiological significance. Glucose and
triglyceride were influenced by both levels of chloride and
potassium (P<0.05), while cholesterol was affected only be
chlorine level (P<0.01), all in non-linear fashion. These
results appear to indicate that some level of
interrelationship does exist between sodium, potassium and
chlorine in young swine. This apparent interrelationship
between the major electrolytes involved in manipulation of
many of the homeostatic mechanisms, known to function in
most species, suggests that the physiological importance of
each in maintenance of potassium balance may, at best, be
subject to question. Perhaps far more important may be the

homeostasis of electrolytes in general.

E. Potassium Deficiency

A potassium deficiency can result from one or a

 

 

 

 

 

Table 5. Effect of Varying K+ and Cl' on Average Daily
Performance in Young Pigsa
Cl%
Average dai y gain and feed efficiency» .07 .13 .18
K, % .3 ADG, kgb .23 .24 .24
F/G, kgC 2.02 2.23 2.28
.6 ADG, kg .25 .24 .24
F/G, kg 2.26 2.19 2.40
.9 ADG, kg .22 .22 .21
F/G, kg 2.12 2.33 2.15
Pooled Means for ADG
C1, % _
.07 .13 .18 xd
K, % .3 .23 .24 .24 .24
.6 .25 .24 .24 .24
.9 .22 .22 .21 .22d
2 .24 .23 .23

 

EAdapted from Combs, 1981.

bSignificant K effect on rate of gain (P<0.05). No
significant Cl effect.

cNo significant effects.

dK effect: .9 significantly different from .3 and .6
(P<0.05).

27

combination of several factors (Jensen et a1. 1961; Cox et al.

1966: Moose, 1967; Linsner et a1. 1980; Potassium In Animal

 

Nutrition, 1981):

 

1.

Insufficient K in the diet and the consequently
inadequate K intake. This is seldom a problem with
swine on cereal grain-soybean meal diets (Miller and
Kornegay, 1983). Potassium levels are often low,
however, in purified and semipurified diets and diets
utilizing fishmeal as the protein source (Jensen et
a1. 1961; Partridge, 1978a).

Loss of K in digestive secretions due to vomiting or
diarrhea. Up to one quarter of the total potassium
in the body may be lost in cases of profuse diarrhea.
Moose (1966) quotes J.E Bertrand: "During periods
of diarrhea (scours), water may be lost at
approximately 40 times the usual rate...carrying with
it practically everything soluble...(inc1uding the
minerals). Replacement of water alone...further
dilutes the body fluids and contributes to the
increased excretion of urine. Sodium is further
depleted and the body tries to maintain osmotic
pressure balance by withdrawing potassium from the
cells. The net result is that both sodium and
potassium may be lost at about 50 times the normal
rate" (Bertrand, Stress and Beef Cattle Nutrition,

Eighth Cattle Feeders Day, Montana Agr. Exp. Station,

28
1964). Although Bertrand's comments were based on
beef cattle, the enormity of potassium loss that can
occur with severe diarrhea alone holds true for all
species. '
High salt (NaCl) consumption increases the
requirement for potassium and can precipitate a
potassium deficiency when intakes are marginal. This
has been directly observed by Grunert et a1. (1950)
and Burns et a1. (1953) in rats and chickens,
respectively, as well as the reverse where potassium
exacerbated a sodium deficiency. Meyer et al. (1950)
observed a rise in plasma potassium that coincided
with a severe sodium deficiency. This, along with
the relationship between sodium and potassium
excretion (Ganong, 1979) suggests that the same
relationship between sodium and potassium
requirements hold true for swine also. Feeding high
salt levels as a means of limiting protein
concentrate intake in ruminants and horses may pose a
potassium deficiency problem in those species, too
(Moose, 1967).
Increased urination: May be due to high water intake
during hot weather or associated with limit feeding
controlled by high salt intake.
Stress conditions: May include cold weather,

diseases with high fevers, hard work or injury,

29
especially if accompanied by substantial blood loss

(Moose, 1967; Linsner, 1980; Potassium In Animal

 

Nutrition, 1981). Potassium supplementation has been

 

shown to reduce symptoms of cold weather stress and
shipping/feedlot stress in cattle (Linsner, 1980;
Crenshaw, 1983).

Changes in levels of body potassium have been related to
certain diseases or illnesses. Conditions which have been
associated with loss of or low blood levels of potassium
include cirrhosis of the liver, hyperthyroidism, injection of
insulin or ACTH, shock, vomiting, diuresis, diarrhea and
carbon dioxide anaesthesia. In turn, low potassium levels
have been associated with hereditary periodic paralysis,
muscular dystrOphy, poliomyelitis and Cushing's Disease
(Midwestern Potash News Letter, 1962).

Potassium deficiency has marked effects on growth and

muscular activity in all species (Linsner, 1980; Potassium In

 

Animal Nutrition, 1981). The first sign observed in pigs,

 

cattle and sheep when receiving a diet containing inadequate
potassium is a reduction in feed intake (Hughes and Ittner,
1942; Jensen et a1. 1961; Cox et al, 1966: Conrad, 1983). The
same authors also report a general depression in growth.

Rough hair coats have been reported for pigs and dairy animals
by Jensen et a1. (1961) and Conrad (1983), respectively.

These authors have also reported muscle weakness, stiffness

and paralysis in pigs and sheep. Jensen et a1. (1961) also

30

reports pigs appear emaciated, listless, have poor feed
efficiency and abnormal cardiac function as indicated by
electrocardiograms (ECG). This has been substantiated by Cox
et a1. (1966). In the study by Jensen et al. (1961)
representative electrocardiograms (ECG's) of 4 pigs were
presented. The ECG's of the 2 pigs on a potassium deficiency
diet for 28 days were distinctly different from those of their
litter-mates, receiving 0.25% added potassium. The QRS and QT
intervals of the deficient pigs were longer on the average,
suggesting the rate of electrical excitement was slowed. The
amplitudes of P, S and T waves of the deficient pigs were more
extreme on the average than those of the controls. Autopsy of
the deficient pigs revealed no gross anomalies or lesions.
Cox et a1. (1966) reported the heart rate of
potassium-deficient pigs decreased slightly over a 28 day test
period. In pigs pair-fed a potassium—adequate diet, in an
amount equal to that consumed by the potassium-deficient pigs,
a slower heart rate was also observed, although to a lesser
extent than in the deficient pigs. Both groups showed
significantly lower heart rates than potassium—adequate pigs
fed SS libitum. Cox et a1. (1966) found the QT, PR and QRS
intervals increased significantly in comparison to the
controls. Other abnormalities observed in potassium-deficient
pigs, but not the controls, were arrythmia and AV block.

Other, more general signs of potassium deficiency

observed in some species include intracellular acidosis,

31
degeneration of vital organs and nervous disorders (Linsner,

1980; Potassium In Animal Nutrition, 1981).

 

 

A daily source of potassium in the diet must be provided

to all animals because it is very mobile in the body.

F. Potassium Toxicity

Under normal conditions, excessive amounts of potassium
are rapidly cleared by the kidney. Toxic concentrations can
develop however, through injury, over-activity or
over-correction of a deficiency by direct infusion of an
electrolyte solution into the plasma or due to the rapid
absorption of potassium from the gastrointestinal tract from
oral administration as a drench (Ward, 1966: Linsner, 1980:

Potassium In Animal Nutrition, 1981). Toxic concentrations

 

 

for most classes of animals have not been established. The
NAS Committee on Mineral Tolerances (1980) have set 3% as the
maximum tolerable level for cattle and sheep. Data for
nonruminants are limited, but a maximum of 2% is tentatively
assigned for swine (NAS, 1980). The most likely source of a
potassium toxicosis problem in livestock production is in
adult cattle. Experiments have indicated, however, that the
animal is well adapted to handling large excesses of potassium
and this does not offer a practical problem under normal

management conditions (Linsner, 1980; Potassium In Animal

 

Nutrition, 1981; Conrad, 1983). In the calf, dog, rat and

 

mature cow, when potassium toxicosis was produced

32

experimentally, plasma potassium levels increased and death
from cardiac arrest resulted (Ward, 1966).

Coulter and Swenson (1970) recorded electrocardiograms of
16 anaesthetized pigs, infused intravenously with an isotonic
KCl solution, to evaluate the effects of potassium
intoxication on the ECGs. They found that an increase in the
T-wave angle occurred in 14 of 16 pigs at a plasma potassium
concentration of 7.0 mEq./L. An increase in T-wave amplitude
and an S-T depression occurred often with plasma K
concentrations of 7.6 mEq./L. The P-wave disappeared at
plasma K concentrations of 8.8 mEq./L in 15 of 16 pigs, but
did not return, in 13 pigs, until the concentration fell to
7.6 mEq./L. Arrhythmia, due to partial heart block, was noted

when K concentration was 9.3 mEq./L of plasma.

G. Variation of Potassium Content among Feedstuffs
Feedstuffs derived from plants constitute the primary
source of potassium in most animal diets. Analytical values

reported in Potassium In Animal Nutrition (1981) show

 

 

variation in potassium contents inherent in grains from
Pennsylvania, the Southwest and samples analyzed by
International Minerals and Chemical Corp, Mundelein, Illinois
(see Table 6). Similar analyses were also reported for
forages. Potassium contents of common feedstuffs are shown in
Table 7. Modern agronomic practices affect the nutrient

content of feedstuffs. Changes in amount and type of

33

Table 6. Potassium Content in Feedstuffs (% K)a

 

 

NRcé

Feedstuff (No. Samples) Value Range Average
Barley (233)b .53 0.99-0.33 0.63
Beet Pulp (8)b .21 0.39-0.15 0.23
Brewers Grains (5)b .09 0.18-0.04 0.09
Corn Dent (88)b .30 0.73-0.2 0.33
Cottonseed Meal (3)b 1.22 2.20-1.03 1.61
Grain Sorghumc .32 0.30-0.16 0.23
Cottonseed MealC 1.22 1.51-1.39 --
Corn 1974 (18)d .30 0.36-0.11 0.25
Corn 1976 (37)d .30 0.52-0.32 0.41
Corn 1979 (43)d .30 0.54-0.24 0.37
Milo 1972 (20)d .32 0.33-0.15 0.24
Milo 1976 (12)d .32 0.51-0.39 0.45
Milo 1979 (8)d .32 0.64-0.32 0.40
Barley 1976 (7)d .53 0.64-0.52 0.57
Barley 1979 (ll)d .53 0.63-0.40 0.52
Wheat 1976 (14)d .40 0.73-0.36 0.51

 

5Adapted from Potassium In Animal Nutrition, 1981.

 

 

bPennsylvania values.

cGrain sorghum primarily from Texas, Oklahoma Panhandle and

Kansas; Cottonseed meal from the Southwestern states.
dGrains from many states and Canada; analysis by IMC,

Mundelein, Illinois.

eNRC, Nutrient Requirements of Swine (1979).

34

Table 7. Potassium Content of Feedstuffs Commonly Used in
Livestock Rationsa

 

 

 

 

 

Feedstuff % K
Low K Sources
Urea 0.00
Corn Gluten Meal 0.02
Wood molasses 0.03
Oyster shell 0.09
Rice 0.15
Corn 0.29
Fishmeal 0.29
Milo 0.35
Oats 0.37
Wheat 0.42
Barley 0.49
Marginal K Sources
Meat scraps 0.55
Hominy feed 0.61
Wheat germ meal 0.78
Wheat shorts 0.85
High K Sources
Wheat bran 1.23
Linseed meal 1.38
Cottonseed meal 1.47
Conditioned fish solubles 1.70
Soybean meal 2.00
Alfalfa meal 2.02
Cane molasses 2.60

Double sulfate of potasssium and magnesium 18.00
Potassium sulfate 41.00
Potassium chloride 50.00

 

5Adapted from Potassium In Animal Nutrition, 1981.

 

 

35
fertilizer used can affect the mineral profiles of feedstuffs
especially. Many feed ingredients are processed by different
methods than they were in the past, altering the nutritive
value of the ingredients. Above all, livestock industries
have been placing more emphasis on higher rates and

efficiencies of production (Potassium In Animal Nutrition,

 

 

1981). Potassium supplementation is still not required in
general, in the H09 and Corn Belt of the Midwest, where corn
and soybean meal are the staple hog feed ingredients.

However, potassium levels in mixed rations must continue to be
evaluated, as goals and management practices change, to assure
that additional potassium is provided if needed for optimum

animal production.

II. Potassium Requirement of the Pig

Until recently, the potassium requirement of animals
received little attention. Most roughages and complete
concentrate rations were thought to provide potassium in
excess of requirements. Nutritionists regarded potassium as
an essential, but noncritical nutrient (Linsner, 1980). A
number of changes have taken place in the swine industry
during the last 25 years which have brought about the need
to examine the requirements of the pig for many nutrients.
These changes include, among others, a change in the pig to
an animal which more efficiently converts dietary amino
acids and energy to a lean, more desirable, meat. This
shift in the end product has required that we more
thoroughly investigate the building blocks required to
produce it (Miller and Kornegay, 1983). Discovery of
apparent interactions of potassium with basic amino acids
and other electrolytes, as cited previously, have lent an
even greater note of urgency to determining how much
potassium is required under different circumstances to
maximize the rate of gain and the efficiency with which we

can raise swine for market.

A. Factors Affecting Potassium Requirement in Other
Species
The primary cause for concern about potassium in dairy

cattle is the substantial amount of potassium excreted in

36

37
milk. Linsner (1980) reports that cow's milk contains
0.147% potassium, 50% more than the level of calcium and
over twice as much as the level of phosphorus in milk.
Higher producing dairy cattle are usually fed a high
concentrate ration, most containing much less potassium then
the traditional roughage feeds, increasing the possibility
of a dietary deficiency among high producing cattle.

In beef cattle, supplemental potassium has been
credited with relieving the performance depressions
associated with stress. Additional potassium is reported to
increase gain of young calves and minimize losses in bred
cows grazing winter range. It is also reported that
supplemental potassium in receiving diets helped to reduce
death loss and growth depression from stresses of diseases
encountered in the first two weeks by feedlot cattle

(Linsner, 1980; Potassium In Animal Nutrition, 1981).

 

 

Leach et a1. (1959) determined that the potassium
requirement of the chick was increased with increasing
protein content of the diet. Burns et al. (1953) found that
the requirements for sodium and potassium had no effect on
one another directly but that a toxic level of one could be
overcome by increasing the other. Under certain conditions
they also observed a slight sparing action between the two
elements. Supplee (1958) investigated the sodium-potassium
interaction in young turkey poults. He found that responses

to potassium supplementation at levels of 0.2% to 0.7% were

38
unaffected when the NaCl content of the diet was increased
from 0.6% to 0.9%.

The sodium and potassium requirements of the weanling
rat were investigated by Grunert et a1. (1950). They found
that the potassium requirement was 0.18% when sodium levels
were 0.1%, but that increasing sodium content to 1.0%
reduced the potassium requirement to 0.15%. Sodium also
provided an initial sparing action as long as the diet

provided a minimum amount of at least 0.09% potassium.

B. Evaluation of the Potassium Requirement of the Young
Pig

One of the earliest attempts to determine the potassium
requirement of the pig was by Hughes and Ittner (1942).

They fed a beet sugar-casein purified basal diet, fortified
with a mineral and vitamin mix, to 50 pound pigs. Potassium
was added to the basal diet in the form of KCl. Hughes and
Ittner found that 1.18 g to 2.36 g potassium were required
per 100-lb. liveweight per day, or a level of 0.15%
potassium in the diet.

This requirement value was disputed by Meyer et al.
(1950). They used a sucrose-casein diet fed 29 libitum to
weanling pigs averaging 38 lbs. initial weight for the trial
in which potassium requirement was determined. After a
preliminary trial to observe for possible effects of

deficiencies of sodium and chlorine, a second trial was

39
performed as a balance study to determine requirements of
sodium, chlorine and potassium. Chlorine levels in the diet
for the balance study were held constant at 0.33% while the
ration contained a constant 0.50% potassium, provided as
potassium phosphate (KZHPO4) Pigs making optimum gains
(1.35-1.38 lb/day), retained 93.69 to 111.33 m9 potassium
per day per kilogram live weight or 40-47% of the weekly
intake. This translated into a recommendation that the diet
should contain 0.23-0.28% potassium to maximize gain. They
calculated an average daily requirement of 5.15 g per 100
lbs. liveweight would be needed to maintain this level of
performance. This figure was approximately double that of
Hughes and Ittner (1942). This was attributed to the nearly
doubled rate of gain of the pigs in the Meyer et a1. (1950)
experiments.

Two experiments at Illinois, by Jensen, Terrill and
Becker (1961), further investigated the potassium
requirement of the weanling pig. The glucose-casein basal
diet averaged 0.015% potassium for both trials.

Supplemental potassium was added as potassium carbonate
(K2C03). In the first experiment, 4 pigs, for each of

two replicates were randomly assigned to one of six
potassium levels, over a range of 0 to 0.5% added potassium
with increments of 0.1%. Performance results for this
35-day experiment are shown in Table 8. Jensen et a1.
(1961) observed an improved performance, in both rate and

efficiency of gain, in pigs receiving up to and including

40

Table 8.

Results of Experiment 1, Jensen et a1.

(1961).

Effect of Potassium Level Upon Pig Performance:

 

Added levels of potassium (%)

 

 

0 0.1 0.2 0.3 0.4 0.5
ADG, lb.a 5y;
Rep 1 0.08 0 17 0.55 0.68 0.60 0.61 0.45
Rep 2 0.04 0.29 0.46 0.72 0.54 0.65 0.45
Average 0.06 0 23 0.50 0.70 0.57 0.63 --
Feed per gainb AyIC
Rep 1 5.26 3.03 1.82 1.75 1.89 1.75 2.17
Rep 2 12.50 2.44 2.00 1.64 1.75 1.67 2.75
Average 8.88 2.73 1.91 1.70 1.82 1.71 --

 

aEach value represents average of 4 pigs per group.

bEfficiencies converted from gain to feed ratios

reported.

CConversion of reported averages for each replicate.

41
a level of 0.3% added potassium. The second experiment, 28
days in length, used 2 pigs per treatment group on a similar
ration. The levels of supplemental potassium used were 0,
0.15 and increments thereafter of 0.05% up to 0.45% added
potassium. The results of this experiment are presented in
Table 9. For this trial, performance of the pigs improved
up to the level of 0.25% added potassium, with no consistent
response above that level. Statistical analyses, of these
two eXperiments revealed that gain was highly significantly
affected (P<0.01) by potassium level in both trials, as was
efficiency of gain (P<0.001 and P<0.01 for experiments 1 and
2, respectively). Estimates of optimum level of
supplemental potassium were made by least squares method
with adjustment for initial weights. The resulting optima
were 0.26% and 0.22% for experiments 1 and 2, respectively,
and owing to no significant differences between the two
estimates, a pooled estimate of optimum level was 0.24%
supplemental potassium. The control ration for both
experiments contained an average of .015% potassium,
indicating that the pigs required approximately 0.26%
potassium to maximize performance. Jensen and coworkers
also reported signs of deficiency in pigs receiving the
basal ration, with no supplemental potassium, including poor
performance, rough hair coats, emaciation, listlessness and
weak, unsteady movement. These pigs also had abnormal

electrocardiograms, as reported earlier.

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42

 

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43

Liebholz et a1. (1966), conducted a series of five
experiments to explore the response of potassium
supplementation of low protein diets in pigs. They used
corn-based diets containing from 7.6% to 24% crude protein,
provided by soybean meal, casein or fish meal. These diets
were supplemental with potassium acetate (KC2H302) at
levels of 0, l or 2% of the diet. They reported improved
gains and feed efficiencies on diets containing up to and
including 18% crude protein, with supplementation of 1%
potassium acetate being more effective than the higher
level. This suggested that for optimum performance of pigs
on low protein diets, the K requirement may be substantially

higher then the 0.26% observed by other researchers.

44
III Bioavailability of Potassium from Various Sources
A. Methods of Determining the Bioavailability of Minerals.

No mineral is ever completely absorbed and utilized.
Some portion is always lost to the normal digestive and
metabolic processes in the animal. Bioavailability is a
relative measure of the portion of the mineral in a given
ingredient that is utilized for some life process, product,
structure, or function by the animal. The response may be a
performance criterion, plasma variable or some other
measurable response. Utilization of the mineral, as
reflected by the response of interest, may be affected by
interactions with other minerals and nutrients, particle
size, feed processing methods, age and stage of growth in
the species in which it is being evaluated and many other
factors. Because of these factors that can affect the
bioavailability of a mineral, many techniques and measures
of response have been used in bioavailability research, from
declaring one source better than another on the basis of a
series of performance trials to comparison of micro-measured
quantities of specific activity of two radiolabeled mineral
sources.

In addition, these comparisons may be referred to by
different terminologies, including percent utilization,
percent apparent digestibility, percent true digestibility,
percent absorption, percent net retention, percent apparent

availability, percent true availability, biological

45
availability, relative biological value and others (Peeler,
1972). These terms are not necessarily the same, but all
may be used for the same purpose. Comparison of any of
these values for both a test source and a standard source
may be used to indicate which source provides more of the
mineral of interest, to the animal, in a form that can be
utilized When ingested.

The most simply-designed tests of bioavailability of a
mineral are those in whidh a growth response, at a given
level of supplementation, obtained with one source is
compared to that from another source. In one such trial,
Long et a1. (1956) arbitarily assigned the response to
phosphorus from dicalcium phosphate in heifers a value of
100. The response of heifers to the same level of
phosphorus from an alternate source was then compared to the
dicalcium phosphate and the "percentage" of dical response
for the test source [(test response/dical response) X 100]
was calculated. A similar response ratio was alluded to,
but not quantified, by Chapman et a1. (1955) in a comparison
of phosphorus supplements for swine. This group used a
series of comparisons of growth responses to rank three
inorganic supplements as well as differentiate between
organic and inorganic phosphorus sources.

Another basis of comparison of the biological
availability of two mineral sources is to make the

comparison at a given level of response. There are also a

46
number of ways to make this type of comparison. Cantor et
a1. (1975) compared the biological availability of selenium
in chicks from different sources to that of Na28e03.
They used a ratio of the level of selenium as NaZSe03 to
which the response on the test source corresponds to the
total level of selenium supplied by the test source, as
determined by chemical analysis. Fritz et a1. (1970) and
Gillis et a1. (1954) used the relative biological value
(RBV) to determine the availability of iron and phosphorus,
respectively. This is the ratio of the "dose" of the
mineral in the standard source to the "dose" required in the
test source to get the same response. A similar technique
is that of slope-ratio analysis, described by Hegsted et a1.
(1968). This method involves calculation of the linear
regression line, Y = a + bx, for each source that is to be
compared. For this line, Y is the response in a given
criterion and X is the amount of the source consumed
("dose") for each individual. All lines must go through the
common intercept, a. A ratio of the slope (b) of the
regression line of the test source to that of the standard
source is then a measure of the relative availability of the
test source to that of the standard source. This ratio can
either be expressed as a decimal, relative to unity (the
standard source), or multiplied by 100 to convert it to a
percentage. This was the technique used by Miller et al.
(1981b) to determine the relative biological availability of

metallic zinc dust, compared to that of ZnO using plasma

47
zinc concentrations.

Miller et al. (1981a), determining the bioavailability
of iron from two sources for young pigs, compared results
obtained from the relative biological value (RBV) ratio
(dose of test source % dose of standard source at same level
of response) using two different responses (net hemoglobin
synthesis or iron retention). Although the theoretical
amount of Hb synthesis, as calculated from Fe retention, was
of the order of the net Hb synthesis measured directly, the
RBV ratio from Fe retention data was higher and more
variable than the ratio calculated from net hemoglobin
synthesis in the first experiment. Miller et al. (1981a)
also compared the results in a second experiment, of the RBV
ratio of Fe retentions to those of the slope ratio
technique. The authors found the relative bioavailability
determined by these two methods to be consistent and similar
to that obtained from the RBV ratio of Hb response in the
first experiment.

Sullivan (1966), in response to errors he considered
inherent in many bioassay studies, attempted to design an
assay he felt would compare sources on a more practical
basis. Using a conventional corn-soybean meal diet for
turkey poults, he measured the bioavailability of phosphorus
by measuring 3 types of responses and combining them to
compute a single biological value for eaCh source. He

weighted the factors, body weight, percent bone ash and gain

48
to feed ratio, so that they provided 55, 40 and 5%,
respectively, of the biological value for a given phosphorus
source. These biological values were then compared to find
the relative biological value (BV). The formulas used for

this combined value are as follows:

BV = (POdXYSight' 9) + (% bone ash) + 10 (gain:feed ratio

 

RBV = Biological value of test source X 100
Biological value of base source

 

In the trials discussed thus far, all nutrients except
for the mineral of interest are normally kept constant
across all treatments to minimize the possible effects of
another variable on the criterion being measured as response
variable. In chicks, calcium is known to influence response
to certain phosphate sources due to the ratio of calcium to
phosphorus in these sources (Peeler, 1972). In order to
overcome the specific potential for a biased result due to
calcium's influence, Damron and Harms (1970), made a
modification of the usual dose—response relative biological
value regime. Damron and Harms (1970) set up graded levels
of the base and test sources as usual for determination of
phosphorus bioavailability but adjusted the
calciumzphosphorus ratios to the optimum calcium level for
each individual source. These calcium levels, determined by
prior work with these sources, were known to result in
minimized response for the criterion measured. This allowed
determination of phosphorus bioavailability with minimal

calcium influence.

49

In the bioavailability assays discussed thus far, all
determinations could be made from experimental data
collected during performance trials. Most other types of
bioassays require fecal or fecal and urinary collections, by
means of a partial or complete balance trial, respectively,
in order to calculate digestibilities, retentions, etc. In
addition, the bioavailabilities in these balance trials may
be determined with or without radiolabeled isotopes of the
mineral of interest. Most balance studies performed measure
the difference between the amount of the mineral appearing
in the urine and feces over a specified period and the
amount ingested from the feed over the same period, in order
to provide net availability or retention. These results may
be misleading unless the balance trial is continued over a
lengthy period, due to fluctuations in body stores and, with
some elements, losses in the sweat and exhaled air
(Underwood, 1981). O'Donovan et a1. (1965) used this type
of balance trial to compare phosphate sources for beef
steers. Endogenous phosphorus excretion was estimated by
collections made during the depletion periods. During the
repletion phase, fecal and urinary collections and fecal dry
matter analyses were made. "True" digestibility for each
source were then computed by correcting intakes for the
phosphorus levels of the basal ration and total fecal
excretion for the amounts, estimated during the depletion,

normally excreted when on the basal ration. Ammerman et a1.

50
(1972) extended the analysis of a simple balance trial to
calculate the "true" absorption (digestibility), as well as
"true" net retention and biological availability of
magnesium for wethers. The absorption was calculated as
before and, by additionally correcting for the loss in
urine, net retention was determined. The biological
availability (BA) was computed by the formula:

[A-B] - [(C-D) + (E-F)]
Bvo, % = [A-B] _ [c_D] X 100

 

Total Mg intake

Mg intake in basal

Total fecal M9

Fecal Mg excretion for basal
Total urinary M9

Urinary Mg excretion for basal

where:

"UFJUOWJ’
II II II ll II II

Underwood (1981) suggests more satisfactory assessment
of the net availability, especially for the major minerals,
could be obtained by means of a comparative balance. This
technique involves comparing the mineral retention of two or
more sources at two or more levels of intake. The net
availability or percent utilization of the mineral in each
source is calculated by the formula:

Improvement in balance X 100

Net availability = , ,
Change in intake

 

where the improvement in balance is the increase in
retention between two levels fed of the same source and the
change in intake reflects the difference between these two
levels.

Studies of mineral utilization in the animal have been

greatly facilitated by the availability of radioisotopes

51
that can differentiate between the endogenous and exogenous
mineral fractions in the feces. The specific activities of
various components sampled during a balance trial are
measured, in order to attribute them to the portion absorbed
and endogenously excreted and the portion that passes
through the gut unabsorbed. Percentage utilization or net
availability from a single labeled mineral source can be

calculated by the formulas (Underwood, 1981):

 

Endogenous = Fecal specific activigy (SA) X 100
Fecal Mineral Endogenous source SA
Unabsorbed = (Total fecal _ (Endogenous
Fecal Mineral mineral) fecal mineral)

Mineral intake-unabsorbed fecal mineral X 100
% Utilization mineral intake

 

Lofgreen (1960) described the procedure for the single
isotope dilution technique which he used to determine
phosphorus availability from four sources for mature
wethers. Body phosphorus was labeled by means of one
subcutaneous injection of neutral, isotonic phosphate
solution containing 32F. After a period of seven days,

a steady state is reached and decline in activity of blood
and fecal phosphorus becomes linear through the collection
period, as monitored by blood and fecal sampling. The
proportion of fecal phosphorus of metabolic origin (as
opposed to that traversing the tract unabsorbed) is
represented by the ratio of specific activity of the feces
to that of the blood plasma. The portion of fecal

phosphorus having passed through the tract, unabsorbed, can

52
be determined by subtracting the fecal:plasma activity ratio
from unity. Fecal activity for any given day was compared
to the plasma activity two days prior to account for the
differences in time required for the isotope to reach the
plasma or feces from a single injection.

Arrington et a1. (1963) used an isotOpe balance to
determine the net retention of phosphorus in cattle for
comparison of different inorganic phosphates. Net
retention, as calculated by the formula:

EZP administeggd orally - (fecal + urinary 32P) X 100
5JP administered orally

 

allowed Arrington and coworkers to correct for differences
in urinary excretion.

Hansard, Crowder and Lyke (1957) combined the single
isotope technique with a comparative balance to determine
the true digestibility of calcium in feeds for cattle.
Endogenous calcium was determined by the general formula of
Underwood (1981) given earlier. A comparative balance
procedure was then employed to allow direct measurement of
calcium absorbed and estimate of endogenous calcium losses.
Fecal values from steers receiving oral doses of labeled
calcium and that of paired animals receiving a single IV
dose of 45Ca were used to determine percentage of
dietary calcium absorbed:

. loo-feoa1450a
% dietary Ca = l-fraction of IV dose of 45Ca in feces

 

53
The percentage absorbed was then used to calculate
percentage of endogenous fecal calcium,

% endogenous _

(% Dietary Ca) ( 100-% )

fecal Ca absorbed fecal Ca
and the daily endogenous fecal calcium in grams:
[(% Endogenous fecal Ca)(Tota1 dietary Ca intake)/100].

The true digestibility (TD) of calcium from that source

could then be computed as follows:

 

TD = 100_[dai y fecal Ca - dailyendogenous fecal Ca]
daily Ca intake

This brief review of techniques used to determine the
bioavailability of a mineral is by no means complete. Many
other techniques and undoubtedly even more variations of all
the techniques exist. Techniques used and criteria measured
when working with one mineral may prove to be totally
ineffective for use with bioassay of another. Sullivan
(1966) briefly reviewed the four main factors he felt
affected results of bioassays and supplied supporting
evidence for the influence of each of the four in
determining bioavailability:

1. Type of basal diet. Sullivan reported several
studies, using purified, semipurified and
conventional diets, that appeared to indicate
different values for a given mineral (phosphorus)
source. The practicality of applying results
obtained with purified diets to the conventional
diets where they will be applied was challenged.

2. Response criterion or criteria used. The
significance of a difference detected in a
non—production related criterion, such as bone ash
determination in poultry sold on the basis of body

weight or grade, was considered. Sullivan related
a number of cases where compounds judged adequately

54

available for body growth were inadequate in
terms of bone mineralization.

3. Specie of animal or bird used. Sullivan points out
the pitfalls of extrapolating results of one group
to another due to differences in utilization or
differentiation between sources.

4. Length of the assay period. The use, or no use, of
depletion periods prior to assay, the effect of the
length of assay on sensitivity to differences
between sources and the importance of measuring a
given criterion during a time span when it is most
critical to the animal were discussed.

Each of these factors, and any others known to affect

the mineral of interest, must be considered when designing a
bioassay experiment and choosing the technique and criteria

to be used.

B. Bioavailability of Potassium in Natural Feedstuffs and

Supplemental Potassium Sources

Very little information has been reported on the
biological availability of potassium from various sources.
Many of the existing potassium bioavailability data were
determined by indirect comparisons or evaluated in terms of
the animal's requirement for potassium when provided by
different sources. Large differences in availability of
potassium should probably not be expected in view of the
solubility and rapidity of absorption of the usual forms of
potassium found in an animal's diet (Peeler, 1972).

In a trial designed to determine the potassium

requirement of yearling steers, Roberts and St. Omer (1965)

added supplemental potassium as KCl or K2C03. No direct

55
comparison of the two sources was made but essentially the
same level of potassium from either source was required to
obtain maximum gain, implying that the potassium was equally
available from either source for fattening steers.

Shelton and Ellis (1965), investigating the use of
buffering agents in all—concentrate lamb rations, used equal
levels of potassium from KHC03 or KCl. Gain responses
were not significantly different. This again implied that
the potassium from these two sources was equally available.

In two experiments with horses, Fonnesbeck (1967)
compared the metabolism of potassium in bromegrass,
canarygrass, fescue, timothy, alfalfa, red clover,
bermudagrass and orchardgrass hays. Fonnesbeck found
potassium retention ranged from -l.8% to 14.5% over a range
of 164-283 g potassium intake per day from the different
hays. This suggests little, if any, differences in the
availability of potassium in these forages.

In a series of reports by Supplee et a1. (1958, 1959,
1965), various sources of supplemental potassium were used
to determine the requirement of turkey poults for optimum
weight gain, bone formation and feathering. A level of
potassium between 0.56 and 0.60% was required, whether
supplemental potassium came from KCl, KZHPO4 or
K3C5H502'H20, in each experiment, indicating

similar bioavailability in the three forms.

56

Based on these reports, Peeler (1972) concluded that,

although solid evidence was lacking, KCl, K2C03,

KHCO3, KZHPO4 and K3C6H502°H20 appeared to

have similar availabilities. Grass and legume hays provided
similar utilization of potassium for horses (Fonnesbeck,
1967).

O'Dell et al. (1972) dissected kernels of various
cereal grains to analyze the mineral content of the various
fractions. A summary of their data for potassium levels is
presented in Table 10. From their results, O'Dell SE nI.
(1972) concluded that high lysine corn contained higher
levels of potassium than the control corn, with a slightly
lower proportion in the germ. They observed that milling
processes that involve degermination of corn or wheat, or
removal of the pericarp and aleurone of rice and wheat,
remove substantial proportions of many minerals, including
potassium, while decreasing phytase content of the processed
feed. This could affect the comparison of potassium
utilization in cereal grains from study to study unless it
can be shown that potassium is equally soluble and
absorbable from all grain fractions. In addition, O'Dell SE
_I. (1972) determined that the chief cations associated with
phytate in corn germ are potassium and magnesium. Their
analyses suggested that the ratios of phytate:Mg:K in corn
germ were 1:3:5, indicating that potassium may occur in a
bound form in corn germ.

Miller (1980), in a review of the bioavailability of

57

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58

minerals, summarized the bioavailability of potassium from
various sources for poultry, swine and ruminants. These
data, based on requirement and plasmal K studies and the
review of Peeler (1972), are presented in Table 11. These
data illustrate the limited number of comparisons of
potassium bioavailability that have been made among
supplemental potassium sources and between supplemental

sources and natural feedstuffs.

Table 11. Bioavailability of Potassium From Various Sources

for Poultry, Swine and Ruminantsa

 

Relative biological valueb

 

 

Potassium Source Poultry Swine Ruminants
KCl 100 100 100
K2C03 -- 100 100
KHCO3 -- -- 100
K2HPO4 100 100 __
K3C5H502-H20 100 -_ __
KC2H302 100 100 --
K2304 100 —— __
Concentrates -- —_ -_
Forage -- -_ -_

 

aTaken from Miller (1980).

bBiological value relative to KCl as the standard (100).

59
MATERIALS AND METHODS
The bioavailability studies on potassium reported here
are incorporated in nine trials. Trials 1 through 5 were
performance trials conducted to re—evaluate the potassium
requirement of the young pig and identify measures useful in
the bioavailability trials. Trials 6, 7, 8 and 9 were
balance trials conducted to determine the relative potassium
bioavailability in potassium carbonate (K2C03),
potassium bicarbonate (KHCO3), corn and solvent-extracted
soybean meal, respectively. Potassium acetate
(KC2H302) was used as the standard potassium source in

the final 4 trials.

I. Potassium Requirement Trials
A. Trials 1 and 2.

Trials 1 and 2 utilized the same experimental design
and will be discussed together. In Trials 1 and 2, 16 three
to four week old pigs, averaging 4.4 to 6.4 kg in body
weight, respectively, were randomly assigned from litters to
8 pens of 2 pigs each. Two of these pens were then randomly
assigned to one of four dietary treatments. After allowing
one week for the pigs to adjust to their new pen mate,
performance was measured over the next 2 or 3 weeks, for
Trials 1 and 2, respectively.

The dietary treatments used in Trial 1 were a basal
diet plus 0, .l, .2 or .4% added potassium from potassium

acetate (KC2H302). Trial 2 used the same basal diet,

60
supplemented with .l, .2, .4 or .8% potassium acetate (.04,
.08, .16 or .32% added K, respectively). The basal diet
used for these two trials is shown in Table 12, along with
the calculated nutrient density of the diet. Tables 13 and
14 present the composition of the vitamin and mineral
premixes, respectively, that were used in all purified basal
diets.

Pigs in Trials 1 and 2 were housed in the east room of
the nutrition laboratory at the MSU Swine Research Farm.
Each pen contained two pigs which were reared in stainless
steel feeding crates (90 X 90 X 76 cm). Each pair was fed
29 libitum from two-hole galvanized steel self—feeders in
the first two trials. Water was provided in individual
stainless steel cups.

Each pig was weighed weekly and feed intake, adjusted
for waste, per pen of two pigs was recorded in a field data
book at the farm. Blood samples (10 ml) from each pig were
taken at the time of weighing according to the method of
Carle and Dewhirst, (1942). These samples were taken by
placing the pig on its back, and while one person held the
pig to restrain movement, a second person removed 10 ml of
blood by puncture of the anterior vena cava using a 3.94 cm,
18 gauge needle attached to a 10 m1 glass syringe. The
needle was then removed from the syringe (to prevent

hemolysis) and the blood was expelled into a 15 ml, labeled,

61

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Table 13. Composition of Vitamin Mix Used in Prified
Basal Dietsarb
Ingredient mg/kg
Thiamine-mononitrate 150
Riboflavin 300
Nicotinamide 2000
Calcium pantothenate 1500
Pyridoxine-hydrochloride 150
para-Aminobenzoic acid 650
Ascorbic acid 4000
Inositol 6500
Choline 54150
d—tocopherol acetate 1000
Folacin 13
Biotin 2.5
Cyanocolbalamin 5.0
Vitamin A palmitate 75
2-methyl-l,4-naphthoquinone 2
Cholecalciferol 0.75
aAdded at 2% of diet.
bIn glucose mondhydrate carrier, Cerelose, DSM Food

Products, Inc., Detroit, MI.

63

Table 14. Mineral Mix Used in Purified Basal Dietsavb

 

 

Ingredient %
NaCl 7.0
K103 .002
FeSO4°7H20 1.36
CuSO4 0.06
MnSO4-H20 0.06
ZnO 0.3
MgCO3 3.6
CaHPO4-2H20 50.4
CaCO3 12.0
CoCO3 0.01
Na;Se01 0.001

 

aAdded at 5% of diet.
bIn glucose monohydrate carrier, Cerelose, DSM Food

Products, Inc., Detroit, MI.

64

plastic tube. Tubes were labeled prior to bleeding to
identify pig number and date of bleeding and 50 l (1000
units per cc) of sodium heparin were added to prevent
clotting and allow harvesting of plasma (Shurson, 1983).
The heparinized blood was centrifuged at 3000 rpm for 15
minutes immediately after all pigs were bled and the plasma
was harvested and placed in 5 m1 labeled, plastic tubes and
frozen and stored at -20°C for later analysis. At time of
analysis, plasma samples were thawed and duplicate
subsamples were diluted with deionized distilled water.
Plasma concentrations of sodium and potassium were then
determined by atomic emission spectrophotometryl, after
dilution of the plasma.

Average daily gain (ADG) values for the individual pigs
were statistically analyzed by least squares analysis for a
linear plateau model (Anderson and Nelson, 1975). Plasma
potassium values were submitted to linear regression
analysis (Gill, 1978) to determine if there were a linear

response to the potassium levels in the diet.

B. Trial 3

Trial 3 was designed much like Trials 1 and 2. The
basal diet was, however, modified and additional blood
constituents were analyzed for possible linear response to
treatment. The modified, purified basal diet used for Trial

3 is presented in Table 15. Levels of supplemental

 

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66
potassium used for the four experimental diets were .1, .2,
.4 or .8% potassium from potassium acetate. In this trial,
the 16 five to six week old pigs randomly assigned from
litters to 8 pens averaged 8.9 kg body weight. Two pens
were randomly assigned to each of four treatments. Due to
the amount of feed wastage observed in the first two trials,
pigs in Trial 3 were fed in individual stainless steel cups,
twice daily, as much as they would consume before the next
feeding. This trial was also conducted in the east room of
the nutrition wing, using the same stainless steel feeding
cages.

The pigs were weighed weekly and feed intake per pen of
two pigs was recorded over the two week experimental period.
Weekly plasma samples, obtained as in Trials 1 and 2, were
analyzed for sodium and potassium, by atomic emission
spectrophotometryl, and chlorine by a coulometric
principle of titrationz. At the time of the final
weighing, an additional 5 ml of blood was also taken. This
additional sample was placed in a labeled heparinized tube
and subsequently analyzed for hemoglobin (Crosby et al,
1954), hematocrit (McGovern et al, 1955), whole-blood K,
whole-blood Na, estimated erythrocyte Na, and estimated
erythrocyte K. Whole blood values were determined by wet

ash digestion of a sample of the blood (Analytic Methods

 

1Model 951, Instrumentation Laboratory, Inc., Lexington,
MA.
2Buchler Digital Chloridometer, Fisher Scientific Company,

Pittsburgh, PA.

Committee, 1960) and subsequent analysis by atomic emission
spectrophotometryz. Erythrocyte K was estimated by
difference, after adjusting plasma values to reflect the
portion of the whole blood represented by plasma. The pigs
were then moved to the west room of the nutrition
laboratory, where a 24 hour urine collection was made.
Urine samples were analyzed for urinary K and creatininel.
Urinary K was determined by atomic emission
spectrophotometric analysis2 of undigested, diluted
samples. The facilities used for this collection are those
described for Trial 5.

Statistical analysis of data from Trial 3 was as that
described for Trials 1 and 2, with additional measures

analyzed for linear response to treatment (Gill, 1978).

C. Trials 4 and 5

In Trials 4 and 5, a semipurified diet was used. Table
16 shows the composition and calculated analysis of the
basal diet used for these two trials. Table 17 contains the
composition of the vitamin-trace mineral mix used for this
diet. Total potassium levels in the four treatment diets
for Trials 4 and 5 were .1, .2, .4 and .8% with potassium

supplied as a potassium bicarbonate (KHCO3).

 

1Sigma Technical Bulletin, No. 555, 1982, Sigma Chemical
Company, St. Louis, MO.
2Model 951, Instrumentation Laboratory, Inc., Lexington,

MA.

68

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69

Table 17. Vitamin-Trace Mineral Premix Used in

Semipurified Dietsa

 

Nutrientb % of mix
Zinc 1.496%
Iron 1.188
Manganese 0.0748
Copper 0.193
Iodine 0.01

USP Units/kg

 

Vitamin A 660,000
Vitamin D3 132,000
19.1159.
Riboflavin 660
d-Pantothenic acid 2640
Niacin 3520
Vitamin 812 3.96
Choline chloride 23,350
Menadione sodium bisulfite complex 440

 

aAdded to diet at 0.5%.

bProvided by vitamin A acetate in gelatin, vitamin D3
supplement, riboflavin supplement, d-calcium pantothenate,
niacin supplement, vitamin 812 supplement, menadione
sodium bisulfite complex, choline chloride, zinc oxide,
ferrous sulfate, manganous oxide, copper oxide,

ethylenediamine dihydroidide and calcium carbonate.

70

Trial 4 was a performance trial with 72 three to four
week old crossbred pigs, averaging 7.9 kg in body weight,
randomly assigned to three replicates. A pen of 6 pigs in
each replicate was randomly assigned to one of the four
experimental diets.

The pigs in Trial 4 were housed in the environmentally-
controlled nurseries of the new farrowing/nursery facility
at the MSU Swine Research Farm. Each pen, containing 6
pigs, measured 1.22 m X 1.52 m, allowing .31 m2 of floor
space per pig. Each pen had a solid concrete sleeping area
(30.5 cm X 1.22 m) and 5 gauge wire mesh flooring throughout
the rest of the pen. A seven-holed galvanized steel feeder
was provided in each pen along with two automatic nipple
waterers. Room temperature was maintained at 27°C for the
first week of the trial, then gradually decreased to 24°C
for the remainder of the trial.

The pigs were weighed weekly throughout the four week
trial. Feed intake per pen of 6 pigs was determined at
these same times by recording the feed added to the
self-feeders from paper bags containing 22.7 kg feed minus
the amount remaining in the feeder (feeder weight at time of
individual pig weighing minus weight of empty feeder). The
data were collected at the farm in the field data book and
later transferred to the permanent record book in the
office.

Triplicate pen mean values of average weekly gain for

the 4 week trial were analyzed by least squares for a linear

71
plateau model (Anderson and Nelson, 1975).

Trial 5 was a balance trial designed to further
quantify the response of urinary potassium to the dietary
treatments used. Four barrows and four gilts from each of
two litters, averaging 7.4 kg body weight, were randomly
assigned to the same four dietary treatments as in Trial 4
(one barrow and one gilt from each litter on each
treatment).

For this balance trial, conducted in the west room of
the nutrition laboratory at the MSU swine farm, the pigs
were reared in individual stainless steel collection cages
measuring 55 x 70 x 76 cm. These cages were equipped with
fine mesh screen beneath the stainless steel mesh floor (1 x
1 cm slots) and above the stainless steel collection tray.
This allowed the urine to pass through the fine mesh screen
to the collection tray, which directed it to plastic
containers beneath, while feces collected on top of this
fine mesh screen. The pigs were removed twice daily from
the collection cages to be fed in individual stainless steel
feeding cages (45 x 90 x 76 cm). They received 150 grams of
their respective treatment diets, per feeding, in stainless
steel feed cups with an equivalent weight of water added to
form a slurry. This insured rapid consumption of their feed
and additional water was added to the feed cups to allow the
pigs to thoroughly clean up the feed. At this time the pigs
were quickly returned to the collection cages to prevent

loss of urine or fecal sample. Room temperature was held

72
constant at 27°C throughout the trial.

Upon assignment to the different diets, the pigs were
allowed a seven day adjustment period to adapt to the
feeding regime and adjust to their respective diet. Feces
were very firm and dry and there was minimal contamination
of urine from feed or feces. At the end of the adjustment
period the collection cages and apparatus were thoroughly
cleaned and prepared for the five day collection period.
Urine and fecal samples were collected daily and the urine
containers were cleaned thoroughly before replacing them.
Daily urine volumes of each pig were recorded and a 30 ml
sample was retained daily for later laboratory analysis.
Fecal samples were allowed to air dry for four days, then
total daily fecal samples were weighed, recorded and finely
ground for later analysis.

The daily urine and fecal samples for each pig were
analyzed in duplicate by atomic emission
spectrophotometry1 for their potassium concentrations and
daily excretion was calculated. Daily values within a pig
were then observed for excretion patterns to determine if
pooled samples (single entire collection) could be used in
the future. Average daily urine excretion and average daily
potassium retention were analyzed for linear response to

treatment (Gill, 1978).

 

1Model 951, Instrumentation Laboratory, Inc., Lexington,

MA.

73
II. Bioavailability Trials

Trials 6, 7, 8 and 9 were balance trials conducted to
determine the bioavailability of potassium in potassium
carbonate (K2C03), potassium bicarbonate (KHCO3), corn
and soybean meal. The experimental design and
depletion-collection regime were identical for the four
trials and they will be discussed together.

For each trial, 6 pigs from each of four litters were
assigned to one of 6 treatments. The same 24 pigs were used
for Trials 6 and 7 and a different group of 24 pigs were
used for both trials 8 and 9.

The twelve pigs of 2 litters were placed on the
depletion phase of the regime, of 10 days duration. Two
pigs out of each litter were assigned to each of three pens
(180 x 90 x 76 cm) in the east room of the nutrition
laboratory at the MSU Swine Research Farm and a 10 m1 sample
of blood was drawn for plasma analysis of potassium
concentration as described for Trials 1 and 2. Pigs were
fed a purified diet (A1) supplemented with 0.3% potassium
(from potassium acetate) in individual stainless steel feed
cups for 3 days, then switched to an identical diet
(depletion) without any supplemental potassium. Table 18
shows the composition of these two depletion phase diets,
which were fed at 250 grams per feeding in each of two daily
feedings. Table 19 gives the calculated analysis of these

two diets. The A1 diet was fed for the first three days so

74

Table 18. Depletion Phase Diets Used in Trials 6, 7, 8 and

 

 

9.
Ingredient % in Al diet % in depletion diet
Isolated soy proteina 20.00% 20.00%
Cereloseb 63.70 64.45
Corn Oil 3.00 3.00
Vitamin Mixc 2.00 2.00
Mineral Mixd 5.00 5.00
(it-cellulosee 5.00 5.00
Aureo-SP 250 0.25 0.25
Methionine-98 0.30 0.30
K acetate 0.75f --
100.00 100.00

 

aArcher Daniels Midland Co., Minneapolis, MN.

bGlucose monohydrate, DSM Food Products, Inc., Detroit,
MI.

CSee Table 13.

eSee Table 14.

eSolka floc, Brown Co., Berlin, NH.

fProvides 0.30% potassium in the diet A1.

75

Table 19. Calculated Nutrient Analysis of Depletion Phase

 

 

Diets.
Calculated % Calculated %
Nutrient in Al diet in depletion diet
Crude protein 16.40 16.40
Lysine 1.12 1.12
Tryptophan 0.16 0.16
Methionine 0.56 0.56
Calcium 0.83 0.83
Phosphorus 0.61 0.61
Potassium 0.32 0.02
Sodium 0.14 0.14
Chlorine 0.21 0.21

 

76
that the length of time on the unsupplemented diet could be
limited to seven days. This allowed us to prevent anorexia
problems, observed in Trial 1 on a diet similar to the
depletion diet (Trial 1, treatment 1), from affecting the
balance portion of the trial. During the final three days
of the depletion phase, the pigs received their feed in a
slurry, made by mixing their feed with an equal amount of
water. At the termination of the depletion phase another 10
ml sample of blood was drawn for plasma K analysis. The
pigs were moved to the west room of the nutrition laboratory
and the second group of two litters were brought into the
east room to undergo the depletion phase of the regime. In
addition, for Trials 6 and 8, as the pigs finished the
collection phase, they were returned to the east room to
repeat the regime for the next trial.

When the pigs entered the west room of the nutrition
lab for the collection phase of the trial, one pig from each
litter was assigned to one of 6 dietary treatments. Tables
20, 21, 22 and 23 present the experimental diets used for
Trials 6, 7, 8 and 9, respectively. Calculated analysis is
the same as for depletion phase diets (Table 19), except for
potassium levels. In Trials 6, 7, 8 and 9, treatments 1, 2
and 3 were the experimental diets for the standard source,
potassium acetate, with total potassium levels at 0.12, 0.18
and 0.24%, respectively. Treatments 4, 5 and 6 were the

experimental diets for the test source. Treatment 4 was

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81
identical to treatment 1 and additional potassium in
treatments 5 and 6 was from the source to be tested.

The pigs were housed in the same facilities for the
collection phase as were described for Trial 5. The method
of feeding was also as described for Trial 5, with intake
for all pigs adjusted to the maximum amount that all members
of the group would consume completely during the short,
twice-daily feeding periods.

Upon assignment to the experimental diets (one pig from
each litter), the pigs began a seven-day adjustment period
to allow them to become accustomed to the feeding regime and
diets and get all pigs in the trial consuming a common,
constant daily intake for several days prior to making
collections. At the end of this adjustment period, the
collection cages and apparatus were cleaned thoroughly and
prepared for a three day collection period. Fifty
milliliters of 50% HCl were added to the urine containers to
maintain the acidity of the urine over the three days of
collection. The collection apparatus was as described in
Trial 5. At the end of the collection period a final 10 ml
sample of blood was drawn for plasma analysis. Total urine
volume for the three days was measured and recorded and a 30
ml sample was retained for later analysis. Pooled fecal
samples, from three days, were oven dried at 70°C, weighed,
recorded and finely ground for laboratory analysis.

Feed, fecal, urinary and plasma samples were analyzed

82

for potassium concentration by atomic emission
spectrophotometry.1 Feed and fecal samples were digested
by the wet-ash procedure of the Analytical Methods Committee
(1960) prior to atomic emission spectrophotometric analysis.
Urine potassium excretion, total K excretion, total K
retention and plasma potassium concentration were used as
response variables in a slope-ratio analysis of the
bioavailability of potassium in the test sources compared to
the standard source (Finney, 1964).

The pairs of pigs assigned to the respective treatments
in trials 6 and 8 were again paired in Trials 7 and 9,
respectively. For Trials 7 and 9, those pairs of pigs were
randomly assigned to the different treatments upon

completion of the depletion phase of the regime.

 

1Model 951, Instrumentation Laboratory, Inc., Lexington,

MA.

RESULTS AND DISCUSSION

I. Potassium Requirement Trials

A. Estimates of Requirement from Gain Data

The potassium requirement was estimated from the gain
data of four trials.

In trial 1, pigs received 0.014, 0.164, 0.273 or 0.495%
total, analyzed potassium in the diet. The linear
regression equation for average daily gain (ADG), derived
from the gain responses (in g) for the first three

treatments, was:

Where: Y = response of ADG in g
X = "dose" or level of total K in the diet (%)

Iterative solving for the maximum X value (X optimum)
that would give the least sum of squared deviations of the Y
values, of the fourth treatment group, from the
corresponding Y optimum yielded an X optimum of 0.30% total
K in the diet. This value, which supported the maximum gain
in Trial 1, was taken to be the requirement of potassium for
this trial. Table 24 and Figure 5 contain summaries of the
data and the plot of the linear plateau response,
respectively, for Trial 1.

Treatment levels for Trial 2 were 0.065, 0.152, 0.230
and 0.456% total K in the diet. For this trial, the linear

regression equation was again derived from the response to

83

84

Table 24. Average Dailnyain of Pigs in Trial 1.

 

 

Analyzed Level of K in the Diet, %
0.014 0.164 0.273 0.495
Number of pigs 4 4 4 4
Average initial weight, kg 4.41 5.12 4.71 4.91
Average daily gain, 9 -2 63 106 114

 

Figure 5. Estimate of K Requirement in Trial 1

300-1

  

 

 

 

m 1
k 0
£1
.3 _
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3; o
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38
100-. I
.; I
2 I
I
2
0- ‘4
. I I I I I
. .2 .3 .4 .5
K level in diet, %
Regression equation: Y = -10.6 + 481.9X

X optimum: 0.30% K in the diet

85
the first three treatments. The X optimum, or level of K
required to support maximum gain for the trial, was
determined to be 0.33% total K in the diet, using the same
method as for Trial 1. A summary of gain data and the
resulting plot are presented in Table 25 and Figure 6,
respectively.

The X optimum for Trial 3 was determined to be 0.26%
total K in the diet. For this trial, the regression
equation was derived from the two lowest treatments, 0.13
and 0.24% total K, and the sum of squared deviations was
minimized for responses to the other treatments, 0.45 and
0.83% K in the diet. A summary of the results for this trial
are shown in Table 26 and Figure 7.

Trial 4 was designed to further substantiate the gain
results of the first three trials. Three replicates of 24
pigs were used, with 6 pigs assigned, within each replicate
to one of the four experimental diets, containing 0.10,
0.18, 0.38 or 0.81% total, analyzed K. A summary of the
triplicate pen mean values, used to estimate the K
requirement, are presented in Table 27. Due to the poor
rates of gain obtained in this trial, the K requirement was
estimated from average weekly gain data for each pen of 6
pigs. The estimate of X optimum for this trial was 0.18% K
in the diet (Figure 8), using the responses on the two lower
levels of K (0.10 and 0.18% K in the diet) to derive the

linear regression equation and minimizing square deviations

86

Table 25. Average Daily Gain of Pigs in Trial 2.

 

Analyzed Level of K in the Diet,

%

 

 

0.065 0.152 0.230 0.456
Number of pigs 4 4 4 4
Average initial weight, kg 6.19 5.73 6.40 6.26
Average daily gain, 9 64 93 167 135

 

Figure 6. Estimate of K Requirement in Trial 2

I

 

 

 

 

400- '

m

. 3oo_f '

G

-H

0

0

2r 0

-H I

:3 . '
I

«3 3

>

0 I
I
|
I
l

0— I
I f I. I l l
01 0‘2 03 .4 05

K level in diet, %
Regression equation: Y = 63.5 + 500x

X optimum: 0.33% K in the diet

87

Table 26. Average Daily Gain of Pigs in Trial 3.

Analyzed Level of K in the Diet, %

 

0.13 0.24 0.45 0.83
Number of pigs 4 4 4 4
Average initial weight, kg 8.6 8.7 9.1 9.1
Average daily gain, 9 280 371 386 398

 

Figure 7. Estimate of K Requirement in Trial 3

500‘ o .

400 ._,.

 

300-

200?

 

Ave. daily gain, 9

100,.

 

 

° III1i I1 i“
.l .2 .3 .4 .5

K level in diet, %
Regression equation: Y = 165 + 837x

X optimum: 0.26% K in the diet

88

Table 27. Average Weekly Gain of Pigs in Trial 4.

 

 

 

Analyzed Level of K in the Diet, %
0.10 0.18 .38 .81
Number of replicate pens 3 3 3 3
Number of pigs 18 18 18 18
Average initial weight, kg 7.8 7.9 7.7 8.1
Average weekly gain, kg
Replicate l 0.59 0.82 0.67 0.83
Replicate 2 ' 0.54 0.72 0.70 0.68
Replicate 3 9;§2_ QLEZ .QLSE ‘QLZZ
Average 0.58 0.74 0.73 0.76
Figure 8. Estimate of K Requirement in Trial 4

Ave. weekly gain, kg

 

 

.J"""""""""

l l I I 7 l

I
.1 .2 .3‘ .4 .5 .6 .7 .8

K level in diet, %

Regression equation: Y = 0.337 + 2.000X

X optimum: 0.18% K in the diet

89
from the corresponding Y optimum for the responses to 0.38
and 0.81% total K in the diet.

The four estimates of K requirement from these trials
(0.30, 0.33, 0.26 and 0.18% K in the diet for Trials 1
through 4, respectively) are not inconsistent with the
published value of 0.26% (NRC, 1979). The precision of
these estimates would be expected to be poor, due to the
small number of pigs used in the first three trials and the
large amount of variation seen in pigs receiving the same
experimental diet for all trials.

In trials 1, 2 and 4, rate of gain was decidedly less
than optimum. In Trial 4, the poor rate of gain appeared to
cause the estimate of requirement to be lower than expected.
Meyer, et al (1950) attributed the difference in the
estimate of the K requirement in their work and that of
Hughes and Ittner (1942) to the poor rate of gain obtained
in experiments by Hughes and Ittner. Although gain was
subpar in Trials 1 and 2 this effect was not apparent,
probably due to the great variability seen in response of
pigs on the same ration.

The modified basal diet in Trial 3 was more readily
accepted by the pigs in this trial and the increased feed
consumption was accompanied by average daily gains more
commonly associated with this size of pig. The absolute
numerical differences between averages for each treatment

were not as great as seen for the other trials, and the

9O

variation within treatment group was much less.

8. Determination of Linear Response to Treatments of Other
Variables

A second objective of the potassium requirement trials
was to identify criteria that provided a significant linear
response to the level of potassium in the diet, for use in a
bioavailability assay. Criteria considered in the four
trials reported here included plasma, whole blood and
estimated cell concentrations of sodium and potassium,
hemoglobin, hematocrit, plasma chlorine and urinary
creatinine and potassium concentrations.

In Trials 1 and 2, plasma samples were analyzed for
potassium and sodium concentrations. In both trials, plasma
K gave a highly significant linear response to the levels of
potassium in the diets used (P<0.001). The linear response
of plasma Na was nearly significant (P<0.10) in Trial 1,
while showing no significant response in Trial 2 (P>0.10).
Tables 28 and 29 summarize these responses for Trials 1 and
2, respectively.

Plasma sodium and potassium were again measured in
Trial 3. In addition, several other blood factors were also
measured. There was no significant linear response (P>0.10)
to any of these measures, including plasma Na, K and Cl,
hemoglobin, hematocrit, whole blood Na and K or estimated

cell Na and K.

91

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92

At the end of Trial 3, a 24 hour urine collection was
made and the samples were analyzed for urinary creatinine
and potassium concentrations. The linear response of
urinary creatinine to dietary levels was nonsignificant
(P>O.lO). Urinary K concentration, however, showed a highly
significant linear response to the treatment levels used in
this trial (P<0.001). Twenty—four hour urine K excretion
also exhibited a highly significant linear response to
dietary K (P<0.001). Table 30 contains a summary of all
factors measured in Trial 3 for linear response to
treatments.

In order to substantiate the results of the 24 hour
urine collection, a five day urinary collection trial (Trial
5) was conducted concurrent with Trial 4, using the same
treatment diets. Samples were collected daily (24 hour
samples) and analyzed for urinary potassium concentration.
Due to day-to-day consistency seen in the urine
concentrations, the average daily urine K concentration and
g excretion per day were tested for linear response to
treatment. Both measures showed a highly signficant linear
response to dietary K level (P<0.001). The results of this

trial are summarized in Table 31.

C. Conclusions in Regard to the Bioavailability Studies
To perform bioavailability assays, one must work below

the requirement for the nutrient in question. The four

93

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9S
estimates of potassium requirement, although varied, are not
inconsistent with the published value of 0.26% K in the diet
(NRC, 1979), due to the small sample size used and within
treatment variation. Use of the published value as the
maximum allowable potassium level in the bioavailability
trials appears to be appropriate.

Few of the urinary or hematological criteria measured
for linear response to treatment showed any potential as a
response variable for the bioavailability studies. Of the
responses measured, only urinary potassium concentrations
and the corresponding urinary excretion values gave
consistently strong linear responses to treatments. Plasma
K gave a highly significant linear response to treatments in
two of three trials in which it was measured. Examination
of plasma K response at higher levels of K supplementation
(>0.25%) reveals great variability within treatment.
Therefore, the possibility exists that plasma K response at
dietary K levels below requirement, as would be used in
bioavailability studies, might prove to give a consistent
linear response also.

Based on these results, a bioavailability assay using
urinary potassium as the primary response variable, for use
in comparing two sources of potassium, appears the most
promising. One may than be able to substantiate these
results by using plasma K concentration as the secondary

response variable.

96
II. Potassium Bioavailability Trials

Four trials were conducted to study the relative
bioavailability of potassium in potassium carbonate
(K2C03), potassium bicarbonate (KHCO3), corn and
solvent extracted soybean meal, using potassium acetate
(KC2H302) as a standard.

Two groups of 12 pigs from two litters were used in
each trial, with one pig per litter assigned to each of the
three standard and three test source diets. Differences in
feed intake between the two groups necessitated use of daily
potassium intake (feed intake/day times potassium content in
the diet) as the fixed variate, X, upon whiCh the response
variable, Y, is regressed. Four response variables were
measured in each trial, including daily urine K excretion
(mg/day), daily total K excretion (mg/day), daily potassium
retention (mg/day) and change in plasma K (mg/d1) over the
10 day test period. Each response was regressed on the
daily K intakes for both potassium sources to determine if a

linear relationship existed between the two variables.

A. Potassium Bioavailability in Potassium Carbonate
(K2C03)

Of the four responses measured in Trial 6, only daily
potassium retention provided a signficant linear response to
daily potassium intake for both the standard source and the
test source of potassium. The results of the linear

regression analyses for all responses are summarized in

97
Table 32.

The daily K retention response was used as the response
of interest for estimating the bioavailability of potassium
in potassium carbonate relative to the potassium acetate
standard. The results of this analysis, summarized in Table
33, showed the potassium of potassium carbonate to be 103%
as available as that in potassium acetate. This is in
agreement with the reviews published by Peeler (1972) and
Miller (1980). Both authors suggested little or no
difference in bioavailability of potassium from organic
salts would be expected.

The accuracy of this estimate of bioavailability would
not be expected to be extremely repeatable, due to the small
sample sizes used. Heterogeneous variance between responses
of pigs receiving the same level of daily potassium intake
was indicated, especially between the six intake levels on

the potassium carbonate diets.

B. Potassium Bioavailability in Potassium Bicarbonate
(KHCO3).

As was the case for Trial 6, only daily potassium
retention provided a significant linear response to daily
potassium intake levels for both the standard and test
sources of potassium in Trial 7.

Pigs in the two groups of two litters of pigs in Trial

7 consumed the same amount of feed per day. This allowed us

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100
to analyze the data with 4 pigs per each of the three daily
potassium intake levels for both potassium sources. One pig
on the .56 9 level of potassium intake for the potassium
bicarbonate source died, during the depletion phase of the
regime, of causes not related to treatments.

A summary of results in the linear regression analyses
for all responses are presented in Table 34. There was no
evidence of heterogeneous variance for the potassium acetate
standard (P>O.25), but substantial evidence of heterogeneous
variance on the potassium bicarbonate source did exist
(P<0.25). This evidence and the small sample size used
again suggest the estimate of potassium bioavailability may
not be very accurate. The results, however, estimate that
potassium from potassium bicarbonate is 107% as available a
that from potassium acetate. The results of the slope ratio
analysis of Trial 7 are presented in Table 35. These
results again agree with the findings of Peeler (1972), that
the organic salts of potassium all appeared to be equally

available for all species.

C. Potassium Bioavailability in Corn

The two groups of two litters of pigs used for this
tLrial again consumed different levels of daily feed intake.
IX summary of the average responses for the corresponding six
leevels of daily potassium intake on each potassium source

alree summarized in Table 36.

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104

As in the previous trials, mean daily potassium
retention was the only response that was related in
significantly linear fashion to the daily potassium intake
for Trial 8. In this trial, however, the regression was
also accompanied by evidence of significant nonlinearity
(P<0.01). Visual inspection of the data and variances of
the individual intake groups (2 responses/intake level)
suggested no overt reason for the nonlinearity. A plot of
mean response vs. intake level did, however, suggest that it
may be due to one response mean, from each potassium source,
lying off the line formed by the other five means in each
case. The bias caused by this one response mean for the
potassium acetate source would be expected to inflate the
estimate of the lepe for the standard. In the case of the
test source, corn, the single response mean that lies
outside of the line would be expected to bias the estimate
of slope from the test source downward. The combined
results of these two effects would result in a lower
estimate of bioavailability than would be expected if these
responses both fell closer to their respective linear
regression curves.

Therefore, the estimate of the potassium
bioavailability in corn in Trial 8, was determined to be 90%
as available as potassium from potassium acetate, but is
probably lower than the actual value. Using the slopes

obtained when the offending data points were ignored (915.97

105
and 875.06 for the standard and test sources, respectively).
a rough estimate of the actual value suggests the potassium
availability may be closer to 95.6% as available as that of
potassium acetate. The results of these slope ratio assays
are summarized in Table 37.

A search of the literature revealed no reports of
estimates of the bioavailability of corn, per se, or
concentrate feedstuffs in general, in any species. In view
of the reports by O'Dell et a1. (1972), of the occurrence of
potassium phytases in the corn germ, one would expect the
bioavailability of potassium in corn to be below that of an
organic salt of potassium. Therefore, the estimate of
90-95% bioavailability of potassium in corn, determined in

this trial, is not unreasonable.

D. Potassium Bioavailability in Solvent-extracted Soybean
Meal

The two groups of two litters of pigs in Trial 9 again
consumed the same amount of feed per day. Therefore, the
data were analyzed with four pigs per each of the three
daily potassium intakes for both potassium sources.

As was the case for the previous three trials, only
daily potassium retention provided a significant linear
response to daily potassium intake levels for both the
standard and test sources of potassium in Trial 9. A

summary of results for the linear regression analyses

106

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107
for all responses is presented in Table 38.

In contrast to the bioavailability trial with corn, no
evidence of non-linearity was apparent (P>0.25) for
responses to either source and heterogeneous variance did
not seem to be a problem. Analysis of the relative
bioavailability of potassium in soybean meal (44%),
summarized in Table 39, shows that the potassium in soybean
meal is 97% as available as the potassium in potassium
acetate. Again, due to the small sample size used, the
accuracy of this estimate may be in doubt. The results are
not, however, inconsistent with the observation of Peeler
(1972) that large differences in availability of potassium
should not be expected in view of the solubility and
rapidity of absorption of the usual forms of potassium

found in an animal's diet.

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CONCLUSIONS
The estimates of potassium requirement in four separate
studies, although varied, were not inconsistent with
the published value of 0.26% K in the diet. Further
investigation of the potassium requirement, if
undertaken, should involve more pigs per treatment
group to enhance the sensitivity of the determination.
The urinary potassium excretion response appears to
offer the most sensitive measure of potassium status
over a wide range of dietary potassium levels. In the
narrow range below the requirement value of 0.26% K in
the diet, daily potassium retention was the only
response that provided a consistent linear relationship
to daily potassium intake. Plasma potassium did not
show a linear response to potassium intake levels in
this narrow range.
Potassium appeared to be highly available in all four
sources tested, in comparison to the potassium acetate
standard. The relative bioavailabilities determined
were: 103% for potassium in potassium carbonate
(K2C03), 107% for potassium bicarbonate (KHCO3),
90—95% for corn and 97% for solvent-extracted soybean
meal (44% CP). These values are consistent with
reports in the literature that little or no differences
in bioavailability should be expected between sources
of potassium. The reliability of these estimates would
be improved if more animals per intake level were used

in future studies.

110

H]

LIST OF REFERENCES

Analytical Methods Committee. 1960. Methods for the
destruction of organic matter. Analyst. 85:643.

Anderson, R.L. and L.A. Nelson. 1975. A family of models
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