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' l "OJ.“ . ______:__,__::_: um mm In "mull w: (w MI 1| mg mum; II 312 L I B R A R Y Michigan State ‘ University - f.- OVERDUE FINES: 25¢ per day per item RETURNING LIBRARY MATERIALS: Place in book return to remove charge from circulation records ABSTRACT BREEDING EFFICIENCY IN A SOUTHERN CALIFORNIA DAIRY HERD by Dennis Vern Armstrong The breeding records of h,OO8 Guernsey and Holstein cows, with 5,9h0 Guernsey and 5,686 Holstein calving records over a 10 year, 10 month period, under the same herd management were used in this study. .Breeding efficiency was measured as the number of days from parturition to first breeding, and the number of days from first breeding to conception. The effect on breeding efficiency of seven factors; breed, month, year, parity, service sire, sire of dam, and multiple births was estimated. Estimates of heritability and repeat- ability were determined. There was no significant difference between the Holstein and Guernsey breeds for breeding efficiency as determined by the "t" test. The data indicate that mean monthly temperature has little or no effect on any of the factors used in this study to measure breeding efficiency, but the year to year management changes do influence breeding efficiency. Ibrity'number did ;affect :the number of days from.first breeding to conception and it could influence days from parturition to first breeding. Service sire did affect days from first breeding to conception, but had no influence on the days from parturition to first breeding. The sire of the dam had no effect on breeding efficiency when measured by number of days from parturition to first breeding. A significant difference was found for days from first breeding to conception. Dennis Vern Armstrong Heritability of breeding efficiency was estimated by doubling the daughter-dam regression. Heritability was estimated to be between .00 and .06 for days from first breeding to conception and .03 to .10 for days from parturition to first breeding. Thus the results indicate that it is not practical to select for breeding efficiency in dairy cows. Estimates of repeatability of breeding efficiency were calculated by the regression of the second record on succeeding record as .09 and regression of second record on subsequent records as .09 for the same cow. BREEDING EFFICIENCY IN A SOUTHERN CALIFORNIA DAIRY HERD By Dennis Vern Armstrong A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Dairy 1961+ ACKNOWLEDGEMENTS The author wishes to express his sincere appreciation to Mr. T. A. Knight and J. E. Elliot and the owners of Adohr Milk Farms, for making these records available, to Dr. G. W. ward and E. K. MacKellar of Colorado State University for the financial help, to Dr. C. A. Lassiter, Chairman of the Department of Dairy, for the computing facilities, also the author is indebted to Dr. L. D. McGillard and A. J. Thelan for the analysis. The author is indebted to W. W. Snyder for his assistance through- out this study and Dr. C. E. Meadows and Dr. R. S. Emery for the help with the manuscript. The author is deeply grateful also to his wife, Sonja, for her continous understanding and encouragement in the preparation of the manuscript. ii TABLE OF CONTENTS I O MRODUCTION O O O O O O O O O O C O C O C O O C II 0 REVIEW OF mm 0 O O O O I O O C C O O O 0 Measures of Breeding Efficiency . . . . . . . . Services per conception . . . . . . . . . . Days from first breeding to conception . . Days from parturition to first breeding . . Calving intervals . . . . . . .,. . . . . . Non-return rates‘ . . . . . . . . . . . . . Factors Affecting Breeding Efficiency . . . . . Breed of cow . . . . . . . . . . . . . . . . III. IV. V. VI. Age of cow . . . . Age of service sire. Year to year . . . Season of year . . Parity number . . . Multiple births . . Mating systems . . Production levels . Post-partum.interval. . Estimates of Heritability . . . . . . Estimates of Repeatability of Breeding Efficiency EXPERIMENTAL PROCEDURE . Source of Data . . . . . Preparation of Data . . RESULTS AND DISCUSSION . Breed . . . . . . . Menth of breeding . Years effect . . . Parity number. . . Service sire . . . Sire of dam . . . . NMltiple births . . . . Estimates of heritability . Estimates of repeatability . . SUMMARY AND PRACTICAL APPLICATIONS BIBLIOGRAPHY . . . . . . iii 0 \OWCDGDGJHIRJ-xlmwm wimp-rum» UL) RDRJADRJFJFJF‘ F1 F4 F1 F1 F’ F4 rerpapdcn\n\n \n Lo L» L» [0 <3 mm CDO\ WW I\) l—‘ 10. ll. l2. 13. 11+. LIST OF TABLES Heritability of Breeding Efficiency -.A ReView of Literatllre O O O Q C O O 0 O O O O O O O O O O O Breeding Efficiency Data . . . . . . . . . . . . . Effect of Mbnth of Breeding on Breeding Efficiency Analysis of Variance of the Month of Parturition and First Breeding on Breeding Efficiency . . . . Effect of Year on Breeding Efficiency . . . . . . . Analysis of Variance of Yearly Effect on Breeding Efficiency . . . . . . . . . . . . . . . Effect of Parity on Breeding Efficiency . . . . . . Analysis of Variance of Parity Effect on Breeding Efficiency . . . . . . . . . . . .. . . . . . . . Analysis of Variance of Service Sire Effect on Breeding Efficiency . . . . . . . . . . . . . . . Analysis of Variance of Sire of the Dam.Effect on Breeding Efficiency . . . . . . . ... . . . . . . The Effect of Multiple Births on Breeding Efficiency . . . . Estimate of Heritability by Doubling the Regression OfDaughteronDam...........c... Estimate of Repeatability Using.All Records . . . Estimate of Repeatability by Correlation of Second Records With Each of the Subsequent Records . . . . ... . iv 17 l8 19 2O 22 23 2h 25 26 29 29 3O INTRODUCTION Efficient reproductiVe performance and long life are essential qualities in the dairy cow and contribute to the sound economics of dairy. The loss from infertility in the United States dairy industry was estimated at 250 million dollars in 1919 by Gibbons (23). A .U.S.D.A. report (13), indicated that 16% of the cows sold from herds on D.H.I.A. were sold because of breeding problems. This compares with the 1963 Michigan D.H.I.A. Herd Summary Report (37) which showed that 19.3% of the cowssold from.Michigan dairy herds were removed for sterility reasons. The need for regular calving to maintain efficient milk production is apparent, but clarification of the influence of genetic and environmental effects on reproductive performance is needed. The object of this investigation was to estimate the repeatability ~and heritability of breeding efficiency, with breeding records compiled over a 10 year period. The effect of several factors which may influence breeding efficiency was estimated. THE REVIEW OF LITERATURE The literature pertaining to breeding efficiency of dairy cattle may be divided into four main categories: measures of breeding efficiency, factors affecting breeding efficiency, heritability, and repeatability of breeding efficiency. Measures of Breedinngfficienqy Breeding efficiency can be measured by several different methods. The discussion of breeding efficiency will be divided into the following topics: services per conception, days from first breeding to conception, days from parturition to first service, calving interval, and non-return rates. Services per conception The most popular method of determining breeding efficiency is the number of services per conception. Successful conception is one which results in a pregnant cow. Conception is an all or none proposition; it is either successful or a failure. Services per conception is based on the number of services required for conception and is sometimes re- ferred to as conception rate. MOrrison and Erb (A0) reported that services per conception varied from 1.5 to over 3.0 for different herds. Services per conception has found a wide use because of the ease of calculation and understanding by both scientist and dairyman. The disadvantage of service per conception as a measure of breeding efficiency is that it fails to distinguish a difference between fertilization or breeding failure, early embryonic death, and loss of time due to silent or missed heats. Cushman (12) reported that 56% of the cows bred were pregnant at -2- -3- first service and 81% were pregnant after three services. Days from first breeding to conception The number of days from first breeding to conception has been used to calculate breeding efficiency. The total number of days from first breeding to conception is used to calculate days from first breeding to conception. For example, a cow that conceived on first breeding would have as her measure of breeding efficiency, zero days. On over 2600 cows, Erb (18) reported an interval of A7 days for the days from first breeding to conception. .Carman (8) found the days from first breeding to conception to be 28': 1.7 in the University herd and A2 : 2.7 in another state owned herd. The disadvantage of using the days from first breeding to con- ception to measure breeding efficiency is that the time of the first breeding may vary, due to management practices such as the desirable time of the year to have cows calving in order to maximize profits. The influence of post-partum interval may greatly bias any measurement using first breeding as part of the measure of breeding efficiency. Days from parturition to first breeding Management practices could influence the days from.parturition to first service. Reproductive disease, post-partum.care, and veterinary management would greatly influence any estimate of breeding efficiency as measured by the number of days from partuirition to first breeding. -Erb and Shaw (19), as well as Hofstad (31) and Scott (50) suggested a minimum of 50 days between parturition and first breeding for a desir- able conception rate. Olds £3 31. (Al) found only 29% of the cows con- ceived when bred at less than 25 days after calving. In the same report they also found the average time of the first heat period to be 30 days post-partum. Calvingginterval The calving interval measured as the number of days from parturition to parturition has been used to estimate breeding efficiency. Legates (32) reported a mean calving interval of A06 days on 2,Al9 records. Hutchinson gt §l° (29) found a mean calving interval of 392 days. The longest calving interval for a group of cows found in the literature was A53 days on 629 cows, reported by Davis (1A). Calving interval has found great acceptance because of the ease of calculation. Non-return rates Artificial insemination units have used non-return rates on first services as a measure of the breeding efficiency of bulls. Non-return rates for first services are expressed in percentages and are based on the number of cows not returning for a repeat service in a given number of days. Sixty to ninety days is the most common interval used to express non-return rates. Non-return rates are not considered an accurate measure of breeding efficiency because some cows may die, be sold, or be bred naturally, or bred artificially to a bull from another.A.I. unit. These cows would be recorded as non-returns. Barrett (2) and Adler (1) found a -5.5% discrepancy between 60-90 day non-return rates and actual pregnancies,-as determined by manual palpation in first service animals. Factors Affecting BreedinggEfficiency There are many different factors affecting breeding efficiency of dairy cattle. The following will be considered breed, age of cow, age of service sire, year, season, parity,.multiple births, mating system,, production level, and post-partum interval. Breed of Cow -5- The difference in breeding efficiency between breeds is a factor which has received considerable publicity. The Michigan Artificial Breeders (36) report higher non-return rates for Holsteins than for other dairy breeds. The 60-90 nonareturn rates on first service were Holsteins averaging 73.5% for 1962 and 72.9% for 1961; Guernseys averaging 67.1% for 1962 and 65.7% for 1961. Boyd (5) found no significant difference between Holsteins, Guernseys, and Jerseys, al- though Jerseys had the lowest services per conception. Hutchinson (29) using both calving intervals and service per conception as a measure of breeding efficiency found no difference between.Aryshire, Holsteins, and Jerseys. Guernseys were found to have a lower service per conception rate than Holsteins in a study by Tanabe and Casida (53). They also found 2.0% genital abnormalities in Guernseys as compared to 18.2% in Holsteins, with an average of 10.6% of cows at slaughter with genital abnormalities which would impare pregnancy. Age of cow Olds and Seath (A3), Miller and Graves (38), Olds _e_t 9;. (1+2), and Davis and Brostt (15) reported a higher breeding efficiency for heifers when compared with older cows. The breeding efficiency of older cows would be lower because they have been subjected to more natural problems, such as calving difficulties, retained placenta, metritis, insemination or natural breeding. In all populations of cows studied to date for reproduction efficiency there is a natural culling effect on the cows that have a low breeding efficiency. Bowling (A),Olds and Seath (A3), Salisbury (A9), Morgan and Davis (39), and Seath gt 3;. (51) have shown that heifers have a higher service per conception rate than cows. -Dawisi(lA), using both service per conception and calving interval, '6‘ found no difference in older age groups for either measure of breeding efficiency. Tanabe and Casida (53) reported a higher fertilization rate and a lower embryonic death rate in younger cows, but the results were not significantly different. Age of service sire Becker and Arnold (3) reported that artificial breeding-associations removed A6% of the bulls from service because of either permanent or temporary low fertility, so that only 35% of the sires remained over three years. Morgan and Davis (39), Erb gingl. (20) and Gildow (2A) found a lower breeding efficiency with advance age of service sire. Miller (38) and Bowling gt.gl. (A) found lower breeding efficiency in 'bulls over six years of age. Year to year Conception rate among normal cows did not vary significantly from year to year, according to Morrison and Erb (A0). Records in sufficient numbers have not been available, so that year to year variation could be investigated in other studies. Management changes from year to year such as.A.I. or natural breeding, changing from fresh to frozen semen, or different veterinary practices could result in a difference in breeding efficiency from one year to the next. Season ofgyear The effect of the season or the month of service on breeding hefficiency could vary, due to the difference in geographic location. Mercier 232 si- (35) found fertility levels of three herds in Canada at different latitudes not to be significant, but reported significance between seasons of year. Temperature changes did have an effect on -7. fertility; the highest percentages of successful services were obtained during the summer and fall. They concluded that the length of daylight could influence the fertility of dairy cattle. Erb gt _a_l. (20), Gowen and Davis (25), Heider gtngl. (30), Morgan and Davis (39), and Trimbarger (55) reported that where high environmental temperatures were found, decreasing hours of daylight were associated with a lower breeding efficiency. The effect of high temperature on bull's sperm.production, and settling capability were demonstrated by Casady'gtngl. (9). Spermatogenesis was impared significantly with temperatures of 85° F. or ‘higher, for periods exceeding five weeks. Parity;number Parity number is the number of successful pregnancies. When cows are grouped by parity number, all cows in the group would have the same number of pregnancies. Parity is used to measure the effect of calving on breeding efficiency. Seath‘gtugl, (51), using services per conception as a measure of breeding efficiency, found no significant difference in parity number. 'Olds gtngl. (Al) found that the first pregnancy required 1.9 more services per conception than the average of all later pregnancies. IMultiple birth A 50% reduction in reproductive efficiency caused by twin births was reported by Pfau gt g1. (A5). The conception rate of cows following twin births was 3.23 services per conception.with a herd average of 2.21. The effect of multiple births on breeding efficiency of any population of dairy cattle would be insignificant due to the low frequency of twinning. Mating sygtems -8- White 93 _a_:_L_. (57), Miller and Graves ( 38) and Fincher and Williams (21) reported that when an inbreeding system using sires mated to their own daughters was followed, over one-half the resulting offspring develop- ed reproductive tracts which were abnormal. .A higher rate of abortions among inbred cattle was reported by Regan £3 21. (#7). Woodward and Graves (60) noted no decline in fertility of inbred cattle when compared to outbreds until the sixth generation. aAfter the sixth generation, a rapid decline of fertility in the inbred group was reported (59). Christian 32 a1. (10) reported that using bulls from one breed had no effect on increasing the conception rate of repeatabreeder cows of a different breed. ' Production levels A correlation of .Oh i 0.01 between milk production and the number of days from parturition to conception was reported by Gaines (22) using h,671 records. Lewis and Horwood (33) showed that low producing cows had shorter calving intervals than high producing cows. Boyd (5) found no significant correlation between number of services required for pregnancy and level of milk production during the first 120 days of lactation. ‘Clapp (ll), Herman and Edmondson (28) and Olds and Seath (hh) reported no correlation between milk production and breeding efficiency. Post:partum interval 1 An average of #7 days from calving to involution of uterus, with an increase of five days for cows which calved abnormally was reported by Olds _e_t El- (Al). After 90 days, 95% of the cows had normal involution of the uterus. Hofstad (31) stated that abortion, metritis, dystocia and retained placenta occured in h0$ of the cows that were bred less .. 'x_ - , .0 -' ‘- b . - . ‘ ' -~ - - ol . 1 .1: , ' a u. . '- ' "" ... ' ‘. ~ . 1.. . ‘. ...{. .. V . 4 ,. - ......:, l;, ...“...o. ,0 -.'. .- 1.; . . . ‘9‘“ than LO days post-partum. Erb and Shaw (19) found a shorter calving interval and fewer services per conception in cows allowed 50 to 60 days to recover from the previous pregnancy. Scott (50), Swenson (52), Trimberger (55), and. VanDermark and Salisbury (56) reported that at least 50 daysshould elapse between parturition and first service for a high conception rate. Estimates of Heritability The estimates of heritability of breeding efficiency range from .00 to .32 as shown in table 1. The value for heritability using services per conception reported by Legates (32) using 398 daughter-dam com- parison was zero. This agrees with Olds (#1) who used 91 daughter-dam comparison and reported a correlation of -.01. .A heritability estimate of .07 was found from data by Pov SEHEl° (#5). Dunbar 32 El. (17) estimated heritability of all breeds in the University of West Virginia herd to be zero. Carman (8) indicated that the heritability of breeding efficiency when measured by days to first estrus, days to conception, and services to conception are zero, or nearly so. An estimate of heritability of .10 was reported by Branton gt 2.1- (6). Wilcox 93 .31. (58) reported the largest estimate of heritability in the literature reviewed.) They found the heritability to be .32 when analyzing the records of 575 cows, over a 30 year period. .10- Table l. Heritability of breeding efficiency -.A review of the literature Measure of Heritability breeding efficiency estimates Reference Calving interval for cows with 3 records .0 Brown.§t'§l. (7) Calving interval for cows ‘with 5 records .01 Brown's: a1. (7) Calving interval .00 Legates, J. E. (32) Services per conception .10 Brandton 23 gal. (6) Services per conception .07 Pov et 21. (#6) Services per conception .03 Legates, J. E. (32) Services per conception herd 1 .08 Carman, G. M. (8) Services per conception herd 2 -.15 Carmen, G. M. (8) Days to conception herd l , .08 Carman, G. M. (8) Days to conception herd 2 -.09 Carmen, G. M. (8) Days to first estrus herd l -.06 Carmen, G. M. (8) Days to first estrus herd 2 -.03 Carman, G. M. (8) Occurance.of first estrus on first record .27 Olds gt a1. (##) Occurrance of first estrus on all records .32 Olds gt El' (##) Non-returns to first service .00 Dunbar gt 21. (17) Cystic ovaries during life .u3 Rice at El- (#8) .11- Estimate of Repeatability of Breedinngfficiency Legates (32) reported repeatability of calving interval to be .13 and service per conception to be zero. Erb (18) found a repeatability of services for conception to be .20. Pov (#6) found the repeatability of services per conception to be .12, the repeatability of days from first service to conception to be .11 and repeatability of regularity of heats .18. Using non-return data as a measure of fertility, Dunbar and Henderson (16) calculated a repeatability of a single reproductive record of a cow to be .03. Branton gt 21. (6) found the repeatability of services per conception to be .10, and recommended that little weight should be given to breeding records in any selection and culling program. Carman (l#) estimated repeatability from the components of variance, and found the value near zero for days to first estrus, days to conception, and service to conception. Repeatability of breeding efficiency of sires in an artificial breeding unit~ varied by breeds, with Holstein .50, Guernsey .#5 and Jersey .31. Harvey (26), using ser- vice per conception, estimated repeatability to be .21 and stated that in determining success of any service, the cow was four to six times as important as the bull. Olds and Seath (##), using single records of the same cow, reported that repeatability of service per conception was .29. EXPERIMENTAL PROCEDURE Source of Data The data used to study and evaluate heritability and repeatability of breeding efficiency, met the following conditions: 1. Complete and accurate records 2. A high level of uniform management over the period studied 3. More than one breed of dairy cattle under the same management #. A high level of uniform herd management over a period of years 5. A herd large enough that the number of records available for a short period of years would be adequate for the genetic estimates indicated. The data for this study were obtained from the records of.Adohr Milk Farms, Camarillo, California, located 60 miles Northwest of Los Angeles. The herd consists of approximately 1500 Holstein and 1500 Guernsey cows of milking age. .All COWS‘Wthh dropped their second calf from January 1, l9#8, through December 1, 1959, were included. Data for the first calvings were not available since most of the heifers were pasture bred. The number of records available for the 10 year 10 month period was 5,9#0 Guernseys and 5,686 Holsteins. The following information was tabulated for each cow included in this study during each gestation period of 250 days or more. 1. Breed, herd number, birth data, sire and dam herd numbers. 2. Parturition number, date of service, service sire for each breeding and calving date resulting from last service. The above information.was copied from the original herd records and then punched on I.B.M. cards, in preparation for analysis. Preparation of Data -12L -13 - A second set of cards referred to as‘a summary for each pregnancy was punched. The following information was included on the-summary cards: 1. Breed, herd number, birth date, sire and dam herd numbers. 2. Number of days from parturition to first breeding indicated as (X). 3. Number of days from first breeding to conception indicated as (Y). #. Crossproducts of X and Y (KY). The summary cards were sorted by breed, year, month, parity, sire of dam, and service sire. The sums of X, Y, and Xwaere totaled for the two measures of breeding efficiency. The heritability of breeding efficiency was estimated by deubling the correlation-of daughter and dam. Repeatability of breeding efficiency was estimated by correlating second records to all records for each cow within each breed. RESULTS AND DISCUSSION The effect on breeding efficiency of seven factors; breed, month, year, parity, service sire, sire of dam and multiple births was estimated. Breeding efficiency was measured as the number of days from parturition to first breeding, and the number of days from first breeding to con- ception. mag. The arithmetic mean, variance, and standard deviation for days from first breeding to conception and from parturition to first breeding are reported in table 2. The "t" test was used to determine if there was any significant differences between the Holstein and Guernsey breeds. There was no significant difference between the two breeds at the .01 level. Table 2. Arithemetic means and variation for measures of breeding efficiency. A. Days from first breeding to conception Breed Records Mean 'Variance Standard deviation Guernsey 5,9#0 31.8 3,#89 59.1 Holstein 5,686 30.6 3,390 58.2 B. Days from.parturition to first breeding Breed Records Mean Variance Standard deviation Guernsey 5,9#0 72.# 1,052 32.5 Holstein 5,686 7#.7 l,0#8 32.# Month of Breeding The nonth of breeding may effect breeding efficiency and was used as a variable because of the climatic conditions which exist in Southern California. If season of year had been used, it could best have been -1#- -15- divided into two seasons; the dry season, May through October; and the rainy season, November through.April. Using only two seasons the effect of total daily sunlight on breeding efficiency could not have been measured with any degree of accuracy. The month of breeding for first breeding to conception was deter- mined by the date of the first breeding, and for parturition to first breeding by the date of parturition. For example, a cow that calved in June and had her first breeding in August, was classified as a June cow for parturition to first breeding record, and August cow for the first breeding to conception record. The monthly average of the combined breeds for first service to conception and parturition to first breeding are shown in table 3. The high month, was 78 days for June, the low month, was 69 days for March for parturition to first breeding. The three low months, January, February, and March, were followed immediately by the three high months, April, May, and June. The three months with the lowest mean daily temperature, January, February and March, had a shorter period of days from parturition to first breeding than the months with the highest mean daily temperature, July,.August, and September. The difference between 71 days for the cool months and 7# days for the warm months was not significant at the .01 level, when tested by the "t" test. The high month for days from first breeding to conception.were 39 days for February, the low months were 27 days for September and November. The coolest three months, January, February and March had.the longest interval, 35 days for first breeding to conception; the warmest three months had an interval of 28 days. The difference was not significant at the .01 level of significance, when tested by the "t" test. ~16— The months with the lowest number-of days from parturition to conception were August, September, and November. January, February, and October were the highest in days from.parturition to conception. The difference between 108 for the high months and 100 for the low months was not-significant at .01 level. The data indicate that temperature as measured by the mean monthly temperature has little or no effect on either measure of breeding efficiency. Table 3. Effect of month of breeding on breeding efficiency. Number Quarterly Parturition First Parturition ‘of mean tempt. to first breeding to to Mggth conceptions 19#8-1959 braggigg con%§£;:3n con%§£;:3n January 1,006 52.9 73 3A 107 February 836 52.9 71 39 110 March 906 52.9 69 35 10# April 985 65.8 73 30 103 May 1,000 65.8 75 31 106 June 1,0h7 65.8 78 32 110 ,July 1,009 72.# 76 29 105 August 968 72.# 73 28 101 September 980 72.# 73 27 100 October 9M6 69.7 73 3A 107 November 891 69.7 73 27 100 December -l,052 69.7 73 31 10# The data in table # indicates that month-effect on breeding efficiency was not significant for parturition to first breeding for either breed. The difference between months was significant for Holstein but was -17- Table #. Analysis of variance of the month of parturition and first breeding on breeding efficiency; A. Parturition to first breeding* Holstein Guernsey Sources D.F.. M.S. D.F. M.S. .Among month 11 1,175 11 6,528 Within month 5,67h 6,6hh 5,928 6,286 B. First breeding to conception* Holstein Guernsey Sources D.F. M.S. D.F. M.S. Among month 11 10,389* 11 #,930 Within month 5,67h #,#19 5,928 h,u98 *Significant at .01% level not significant for Guernseys when breeding efficiency was measured as days from first breeding to conception. Years Effect The major changes in management which could influence breeding efficiency could best be expressed if the data were divided into years. Artificial breeding at Adohr Farms was very primitive during the first few years it was practiced. As technology of handling semen advanced, breeding efficiency improved. Table 5 shows the combined Holstein and Guernsey data indicating the year effect on breeding efficiency. One major management change made during the years these data were taken: a longer post-partum interval was allowed before first service. The post-partum interval increased from 57 days in l9#9 to 78 days in 1958. This was accompanied by a decrease in the yearly mean for the days from :first breeding to conception of 95 days in l9#9, to 23 days in 1958. «A43 days from parturition to first breeding increased, a decrease in the -18- days from first breeding to conception was noted. This resulted in a decrease in the days from parturition to conception. The data pre- sented in table 6 indicates that there was a significant yearly effect on first breeding to conception for both Holsteins and Guernseys. The year effect on breeding efficiency as measured by parturition to first breeding was significant for Holsteins, but not Guernseys at the .01 level of significance. It could be concluded from these data that the effect of year to year management change could influence post-partum interval. The largest change in days from parturition to first breeding occurred between 1950 vs. 1951, while there was little change in days from first breeding to conception and days from parturition to conception. Table 5. Effect of_year on breeding efficiency Days from Days from Days from parturition first breeding parturition Number of to first to to Egg; congeptions breeding conception conception 1949 195 57 95 152 1950 #61 57 8h 1A1 1951 609 79 66 1h5 1952 965 79 - 37 116 1953 1,282 70 29 , 99 195# 1,#52 69 2# 93 1955 1,562 72 21 93 1956 1,527 76 2A 100 1957 1,622 77 2A 101 1958 1,659 78 23 101 1959 181 75 h 79 -19- Table 6. .Analysis of variance of yearlypeffect on breeding efficiency A. Parturition to first breeding Holstein Guernsey Source D.F. M.S. D.F. M.S. Between years 1h 9,636 15 282,97#* Within years 5,671 6,#50 5,92h 5,586 B. First breeding to conception Holstein Guernsey Source D.F. M.S. D.F. M.S. Between years_ 1# 166,732* 15 119,536* Within years 5,671 3,677 5,92# #,208 *Significant at .01% level Parity Number The age of cow was indicated by parity number. Grouping by parity number assures that all the cows within a group have all had the same number of pregnancies. The stress on the cow's reproductive tract which could result in‘a change of breeding efficiency is better measured by parity number than by age. .Information on first parity was available for only 250 of the cows, because most of the heifers were pasture bred and breeding records were not available. Of the #,008 cows which had two pregnancies, only 1,181 had five pregnancies or more; 75 had ten pregnancies or more; and 3 cows had fourteen pregnancies. The data in table 7 shows the number of cows for each parity number, the mean for both measures of breeding efficiency, and the total days from parturition to conception. Number of days from first breeding to conception was the longest, 50 days, for the twelfth parity, with only -20- fifteen records available. The shortest number of days for first breed- ing to conception was 17 days for the first parity, with 250 records. Parity numbers 1, 2, 3, #, 5, 6, 7, 8, and 10 all were below the arithmetic mean of the population for days from first breeding to conceptions. Number of days from parturition to first breeding was longest, 85 days, for parity 1# with only three records, and shortest, 70 days, for parity 12 with fifteen records. Parity number two had a longer parturition through first breeding, 79 days; first breeding to conception, #0 days. Both are considerably larger than the arithmetic mean for the two measures of breeding efficiency. Parity numbers 2, 3, 9, l3 and l# were all longer for parturition to first breeding than the arithmetic mean. Parity numbers 5, 7, 8 and 12 were below the arithmetic mean. Table 8 shows that parity effect on breeding efficiency was significant for first breeding to conception for both breeds. Parturition to first breeding was significantly affected by parity for the Holsteins. Parity effect for Guernseys was not significant for parturition to first breeding. These results indicate that parity number does influence the number of days from first breeding to conception, and it could influence days from parturition to first breeding. The mean days from parturition to conception did not appear to be influence by parity number. Service Sire Adohr Farms used 86 Holstein and 127 Guernsey service sires during the ten year and ten month period when these data were obtained. The largest number of conceptions for a Holstein service sire was -21.. Table 7. Effect of_parity on breeding efficiency. Number of Parturition 1st breeding Parturition Parity no. conceptions to 1st breeding to conception to conception (Days) (Days) _CDays) l 250* -- 17 -- 2 #,008 79 #O 119 3 2,617 7# 27 101 b 1,720 73 25 98 5 1,181 72 25 97 6 777 73 28 101 7 #99 72 ‘ 25 97 8 289 72 30 , ' 102 9 159 77 33 110 10 75 73 ‘ 29 102 8 ll 36 73 37 110 12 15 70 50 . I 120 13 7 75 #5 120 l# '3 85 #2 127 '*Most heifers were pasture bred for first pregnancy. 911, and 1,07# for a Guernsey sire. With less than six conceptions there were 71% of the Guernsey service sires and 50% of the Holstein service sires. Only cows with two or more reproductive records were used for this study, so it is possible for those bulls reported.with less than six conceptions to actually have more. Also this study came from a fixed ten year and ten month period; therefore, some of the service sires were on the beginning or end of their service period in the herd. -22- Table 8. Analysis of variance of parity effect on breeding_efficiency. A. Parturition to first breeding Holstein Guernsey Source D.F. M.S. ' D.F. M.S. Between years 13 59,136* 13 1,022 Within years 5,672 6,513 5,926 6,298 B. First breeding to conception Holstein Guernsey Source D.F. M.S. D.F. M.S. Between years 13 32,329* 13 79,517* Within years 5,672 u,366 5,926 h,335 *Significant at .01 level The analysis of variance of service sire effect on breeding efficiency is presented in table 9. A significant difference is shown when breeding efficiency is measured by the number of days from first breeding to conception. Parturition to first breeding is not signi- ficant, as would be expected, because the service sire would have no effect on days from parturition to first breeding. -Bulls used in artificial insemination units are usually selected for their ability, to transmit for production rather than on their transmitting ability for fertility. If heritability for fertility in bulls is low, then except for the need for good conception, there would be no advantage in selecting for bulls with better than average transmitting ability for fertility. These results indicate that the service sire does influence the days from first breeding to conception, but has no influence on the days from parturition to first breeding. Service sire influence on -23- days from first breeding to conception is through the fertility level of the service sire. Table 9. Analysis of variance of service sire effect on breeding efficiency. A. Parturition to first breeding Holstein Guernsey Source D.F. M.S. D.F. M.S. Between years 85 8,609 126 3,#O# Within years 5,600 6,782 5,813 6,3h9 B. First breeding to conception Holstein Guernsey Source D.F. M.S. D.F. M.S. Between years 85 19,920* 126 12,182* Within years 5,600 #,l95 5,813 #,332 *Significant at .01 level. Sire of Dam Sixty-nine percent of the sires of the Guernsey dams and sixty percent of the sires of the Holstein dams had less than ten daughters used in this study. Table 10 shows the analysis of variance for effect of sire of dam on breeding efficiency. The sire of the dam had no effect on breeding efficiency when measured by number of days from parturition to first breeding. A significant difference was found when days from first breeding to conception was used as the measure of breeding efficiency. Multiple Births The Holstein herd had 126 sets of twins born in 5,686 calvings for a twinning rate of 2.2%. The Guernsey herd had 116 sets of twins in -2#- 5,9## calvings for a 1.9% twinning percentage. The effect which multiple births have on breeding efficiency during the pregnancy follow- ing the multiple birth, was measured by "t" testing for a significant difference between the population and reproductive record following the multiple births. Table 10. .Analysis of variance of sire of the dam effect on breeding efficiency; A. Parturition to first breeding Holstein Guernsey Source D.F. M.S. D.F. M.S. Between years 96 1,525 1## 1,665 Within years 5,589 6,721 5,795 6,h01 B. First breeding to conception Holstein Guernsey Source D.F. M.S. D.F. M.S. Between years 96 10,763* 1## 7,707* Within years 5,589 #,321 5,795 #,#19 *Significant at .01 level The days from first breeding to conception were significant for the Holsteins, but not for the Guernseys. There was no signifi- cant difference for days from parturition to first breeding in either breed. These data are shown in table 11. These results indicate that multiple birth has no effect on breed- ing efficiency when measured by number of days from parturition to first breeding. The number of days from first breeding to conception was significant for Holsteins but not Guernseys. The number of days from first breeding to conception was approximately 10 days longer for n both breeds, indicating a loss of one-half a service for each conception following a multiple birth. Tabii,ll° The effect of multiple birthsfion breeding efficiency. A. Holstein Measure of Reproduction reqords breeding following a multiple . efficiency, birth Holstein herd ' No. of Mean” No. of 5’ Mean births . (days) births (days)' Parturition to lst breeding 126 77.2 5,686 7#.7 First breeding ' to conception 126 #3.1* 5,686 30.6 B . Guernsey Measure of Reproduction records breeding following a multiple efficiency birth Guernsey herd 7v- No. of Mean No. of 55* Mean births (days) births (days) Parturition to 1st breeding 116 *76.8 5,9## , 72.#. First breeding - to conception 116 #1.6 5,9## ' 31.8 '*Significant for ”t" test at .01 level of significance. Estimates of Heritability Some methods used to estimate heritability compare animals Which ’are closely related with animals which are less closely related than they average of the population. 'An estimate of heritability is necessary if 'one is to select accurately for a trait such as breeding efficiency. I A low heritability estimate would indicate that the variation in this measure of reproductive efficiency would not be common, since nature has -26- selected and continues to select for improved reproductive efficiency. The correlation of paternal half-sibs is used to estimate heritability of breeding efficiency with any of the previously discussed units of measure- ment, service per conception non-return rate, calving interval, etc. Pa- ternal half-sibs have only one-fourth of their genes in common, as they are only one-fourth related. The correlation of paternal half-sibs must be multiplied by four to estimate heritability. Daughter-dam correlations have been used to estimate heritability of breeding efficiency. The relationship of daughters to their dams is one-half; therefore the correlation must be multiplied by,two. The daughter-dam correlation is the fraction of the phenotypic variance that is additive genetic. The within sire regression of daughter to dam is another common method of calculating heritability. Daughter-dam regression can be used on single record or an average of all records to estimate heritability. The within sire daughter-dam regression is multiplied by two to estimate heritability. The correlation between full sibs or identical twins can also be used to estimate heritability of breeding efficiency. The range is from minus one to plus one if the method used to estimate heritability is a correlation. When correlations are used to estimate heritability, correlation coefficients between minus one and zero are zero for all practical purposes. Heritability estimates of reproductive efficiency were calculated by doubling the correlation between the dam's performance and the per- formance of their daughters. Correlations were calculated for the second reproductive perfor- mance of both dam and daughter. Correlations were also calculated from -27- all the records of the dam and daughter. Second_records were used in- stead of first records, because most of the cows were pasture bred at first pregnancy; therefore reproductive performance records were not available. When a dam had more than one daughter, the dam's record waS" repeated for each daughter used in the correlation. There were 958‘ daughter-dam comparisons for the Guernseys, and 913 for the Holsteins when all records were used in the correlations. These c0mparisons were reduced to 950 Guernsey daughter-dam comparisons and 912 Holsteins used when second records only were used. The number of records used for each breed was not the same, because some cows were purchased after their second reproductive record. Estimates of heritability when days from parturition to first breeding was used to measure breeding efficiency, varied from ,03 to .10. When breeding.efficiency was measured by number of days from firSt breeding to conception, heritability estimates varied from .00 to .06. When only second.rcproductive records were used, heritability estimates were lower than if all records had been used. These data are shown in . table 12. These results indicate that most of the variation in days from parturition to fir:t breeding and days from first breeding to conception among dairy cattle is nonegenetic. Estimate of Repeatability Repeatability is a measure of the tendency for observations on the .samo oow to be more aliie than observations on different cows. Re-' peatability is also a measure of the upper limits of heritability. 7It has been assumed that length of reproductive cyCle or reproductive per- (formance is repeatable, and that a cow with a poor reproductive per- formance during her first reproductive record will have similar repro- -28- Table 12. Estimate of heritability by doubling the regression of daughter on dam. Holstein .All records Second records only First breeding to conception .020 .O6# Parturition to first breeding .056 .102 Guernsey First breeding to conception ---.O3# ---.O3# Parturition to first breeding .026 .082 ductive performances throughout her life. In this study repeatability was measured as the regression of the second reproductive record on succeeding records for the same cow. Repeatability was measured also as the regression of the mean of any reproductive record on the mean of any following record. Table 13 shows the estimate of repeatability for all records and table 1# only second records. Estimate of repeatability was near .10 or 10%. Therefore, it appears from these data that a single breeding record of a cow is not a good measure of her future reproductive per- formance, and little weight should be given to it in any selective or culling‘program. Table 13. Estimate of repeatability using all records. Holstein Days from parturition to first breeding Days from first breeding to conception Guernsey Days from parturition to firSt breeding Days from first breeding to conception Correlation .0999 .09u7 .0999 .0965 -29- Table 1#. Estimate of repeatability by correlation of second record with each of the subseqeent records. izgord/subsequent Days from first breeding Days from parturition record to conception to first breeding Holstein Guernsey Holstein Guernsey, 2/3 .0989 .0989 .0999 .0999 2/A .0998 .0993 .0999 .0999 2/5 .0997 .098h .0999 .0999 2.6 .0996 .0990 .0999 .0999 2/7 .0997 .0985 .0999 .0999 2/8 .0955 .0987 .0998 .0999 2/9 .0979 .0991 .0997 .0999 2/10 .0958 .099# .0998 .0997 2/11 .0981 .0818 .0999 .0999 2/12 .0758 .0999 .0999 .0996 2/13 - .0999 - .0999 SUMMARY AND PRACTICAL APPLICATION The breeding records of #,008 Guernsey and Holstein cows With 5,9#0 Guernsey and 5,686 Holstein calving records have been studied to determine the effects different environmental factors could have on breeding efficiency. The environmental factors measured were breed, month, year, parity, service sire, sire of dam and multiple birth. Breeding efficiency was measured as number of days from first breeding to con- ception and number of days from parturition to first breeding. The heritability and repeatability of breeding efficiency was also estimated. The results of this study indicated that breed, season-as measured by mean monthly temperature and multiple birth do not effect breeding efficiency. Year, parity, service sire, and sire of dam did effect breeding efficiency depending upon which measure of breeding efficiency was used. The estimate of heritability was found to be between .06 to .10. The low heritability would indicate that selection for breeding efficiency (fertility) when measured by days from first breeding to conception and parturition to first breeding can not be very effective and would only decrease the effectiveness of selection for such economical traits as milk production. 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