. . M WWI" ‘1”! “W W! 301107 9807 This is to certifg that the thesis entitled V". A Study of Lamb Mortality in the Michigan State College Rock -‘n l ' M,‘ .- ‘m w." presented hg Ganapathy Vonkatachalun has been accepted towards fulfillment oi the requirements for ““19 39 degree iILMiEQ-l Husbandry . ' \’ s 7 ‘ s.‘ ) e? /‘. , //Z .1 {My _ l _‘# VV , Major professor Harem: t 9114. 19.1.1. LIBRARY Michigan Statc University PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. .' a. I \" . f . 4 _l |\ i“ .t “3‘ r "‘ . . u .i \[g l l» I. ‘\ \ Q 'l . t Y” a ’ . -. iv . I 1.. l \ _ l 'V C. C ‘I ‘ I ‘. . . ‘ '3' 'L- l ‘ | .' L ‘ \. 3‘0 ' O. . 4 q u r A.STUDY 0F LAMB MORTALITY IN THE MICHIGAN STATE CQELEGE FLOCK. By GANAPATHY VENKATACHALAM. A.TEESIS Submitted to the School of Graduate Studies of Michigan State College of Agricultm'e and Applied Science in.partial fulfillment of the requirements for the degree of MASTER OF SCIENCE. Department of ANIMAL HUSBANDRY. 19h7 CONTENTS . ACKJ‘IW‘I‘S.......-....... INTRODUCTION............... REVIEWOFLITERATURE........... Foetal Circulation, Figure l . . Explanation for Figure 1 . . . . Persistency of Ductus Arteriosus Patency of Foreman Ovals . . . . Lamb Losses in Other Floolcs. . . smmnormnnmrrmm......... Analysis of Lamb Crop, Tables I, Year Variation, Table IV . . . . Individual Sire Effect, Table V. II and III. Sex Difference, Table VI . . . . . . . . . . Single and Multiple Birth Difference, Table VII. POST-MORTZEMFIIIDINGS........... OpenForamen Ovale . . . . . . . Freaks............. Possible Inherent Causes . . . . Tracing of Pedigrees . . . . . . DISCUSSION................ SUFMARYANDCONCLUSIONS. . . . . . . . . . BELIWAPHY O O O O O O O O O O O O O 0 0 191183 17. 19. 20. 20. 21. 21. 22. 27. 29. 31. ACKNOWLEDGMENTS. The author is deeply indebted to the following professors for their timely help and advice which acted as a catalytic agent for the successful Operation of this experiment. 1. Dr. R. H. Nelson, Ph.D., Associate Professor, Animal Husbandry Section, Michigan State College. 2. Dr. F. J. Thorp, Ph.D., Research Professor, Animal Pathology Section, M. S. C. lll.r l{|l[.ll[[[[[llll INTRODUCTION. It is in order to explore the possible hereditary causes of the high.rate of lamb mortality in the Michigan State College Flock that the author has made earnest attempts while compiling this ‘matsrial. From the results of 700 autopsies performed by Dr. L. B. Scholl, during 15 years (up to 1939), it has been noted that parasit- ism and feeding problems constituted the chief factors of loss in sheep raising in Michigan, as a whole. But, to-day, under strict sanitation and a well-balanced system of feeding and careful manage- ment, the shepherd is confronted not with feeding problems but with actual breeding problems. A study of the previous autopsies done by Dr. L. B. Scholl reveals that pneumonia has taken a.heayy toll of sheep losses; and at least one case of patent foramen ovals has been.recorded. The present analysis deals only with lamb mortality, excluding sheep. From.a.more detailed post-mortem.examination and.rscordings done during 3 years (1915 to 19h?) by Dr. F. J. Thorp, and his assistant, Mr. M. L. Gray, of the Animal Pathology Section, it has been possible to show a definite cause of congenital abnormalities as a main factor for heavy lamb loss. The abnormalities include patent foramen ovale of the heart, freaks and still-births. Some deaths are also attributed to undetermined causes. 80, this analysis leads to the conclusion that, besides the various causes already known, heredity also plays an important role in lamb mortality. Foetal circulation. REVIEHOFIITI'RATLIRE 3. lfll'll‘llllllll‘l D. A. a. 3.3. Pea. H. a.v.c. H. P. p.v.c. D. V. U. C. P. EXPLANATION for Figu_re 9;. . Right Atrium (Right Ain'icle). - Right Ventricle. .- Left Atrium (Left Auricle). u. Left Ventricls. . Foreman Ovals (Via Sinistra). - Pulmonary Artery. . Lungs (Right and Left). - Pulmonary Vein. - Ductus Arteriosus. - aorta. . anterior aorta. posterior aorta. . Head of the Foetus. - anterior vena cava. - Hind Parts of the Foetus. :- posterior vena cave. - Ductus Venosus. - Umbilical Cord (Havel cord). - Placenta. 5. Placenta formed by the maternal and foetal membranes is the foetal organ of nutrition, respiration and excretion. Umbilical £0332: (Navel cord) consists of 2 umbilical arteries, 2 umbili- cal veins, the eJlantoic duct (urachus) and many small blood vessels - all covered up by the Whartonian Jelly-like connective tissue. It is important to note that the Eustachian valve is absent in the foetal heart of lamb. Although the anterior and posterior vena caves carry blood respectively from head and hind parts of the foetus, they pour into right atrium where a mixing of blood is said to take place. Later on, a portion of the mixed blood is directed into left atrium via the Foreman ovals, and the other portion into right ventricle through the right auriculo-ventricular opening. In the adult circulation, the foreman ovals closes, the duc- tus arteriosus and ductus vanosus obliterate; and hence, these are all rendered functionless after the severance of umbilical cord and placenta at birth. This is what happens in the case of normal circulation. Persistency of m Artsriosus. A knowledge of the closure of ductus arteriosus throws light on the normal and abnormal conditions of the latter. The closure of ductus arteriosus is said to occur in two different stages (Barclay, Franklin and Prichsrd, 19,45). 1. Physiological occlusion takes place very soon after birth. This is called the Functional closure. 2. Anatomical occlusion requires a very consider- able time for its completion. This is called the Anatomical closure. 6. Ductus Artsriosus closes at least functionally after birth - 1t minutes after ligation of the umbilical cord. Failure to ligature the cord delays the closure of the ductus. However, the functional closing is immediate within 3 hours. The anatomical obliteration takes place more leisurely in three months of life (Smith, C. A., 1916). The closure is not effected by any nerve pathway or neuromuscular reflex but it is due to the sphincter action of the intima layer. Immediate closure is due to increased oxygenation of foetal blood. So, a period of postnatal enoxia is suspected cause of patent ductus arteriosus. Since the ductus is more muscular with a potential sphincter the closure may be due to muscular effect rather than nem'omusculer one. A ductus closed for only a short time (as shown by I-rey) may be found to be open post-mortem. If the foetus deteriorates a clossdductus may reopen. However, in a healthy foetus, the closure is rapid, complete and lasting. Patsncy 23 Foreman 9333.3. It has already been mentioned that there is no Eustachian valve in the foreman ovals of the foetal heart of a lamb; and even a projection that some writers have taken for the rudiment of this valve proves, on probing from the outside, to be nothing but a slight infolding of the wall. "Guy ropes" (free borders of cords) are a characteristic feature of foreman ovals in lamb's heart. This structure favom's a mechanical rather than the neuromusculsr process for the closure of foramen ovale. Closure is due to increased pulmon- ary venous return induced by the onset of respiration. It has been observed that foreman ovals can close before the cord is tied and while the ductus arteriosus is still patent. Closure of the ductus follows 7. the closure of foreman ovals, cessation of the placental circulation being a necessm‘y preliminary (Barclay, Franklin and Prichard, 1915). The closed foreman ovals may reopen after some time if the foetus deteriorates but in a healthy foetus, the process is rapid and. the effect permanent. The heart attains its postnatal functional inde- pendence usually after the closure of foramen ovale and ductus arteri- osus. If the umbilical vessels do not close down at, or soon after birth the lamb will die. Patency of foreman ovals or of the ductus arteriosus may have a very serious consequence such as predisposition to pneumonia and bacterial endocerditis. m: In man, the continued patancy of ductus arteriosus for years after birth is a common occurrence but the condition predisposes toward bacterial endocarditis and is in itself a danger because of the additional load placed upon the left ventricle which may lead to cardiac decomposition (Windle, W. F., 19%). Lamb Loss in Other Flocks. A study was made of the 25 years of records on the flocks kept by the Ohio Agricultural Experiment Station (Bell, 19“). These records were quite complete in that they included a lamb mortality record in addition to the usual ones kept in a modern bm'n. During the past 25 years much attention had been given to the feeding and nutrition of the pregnant and nursing ewes; and deliberately the nutritional in- fluences had been eliminated as a cause of mortality. Then, during the ten year period from 1935 to 19% inclusive, an analysis was made to study the loss of foetuses which failed to sur- vive. The barn consisted of both purebred and grade sheep which were classified into fine wool breed and mutton breed. A total of 1,309 pregnancies occurred resulting in the development of 1,702 foetuses. By the time the lambs averaged two months of age, 1, 371+ lambs were surviving. Altogether, 328 foetuses failed to survive. Roughly, one out of every five foetuses carried was either aborted, born dead, or died within the first two months after birth. The mortality rate was 19.27 per cent. It is interesting to note here that the mortality rate of lambs 2 months old in the M. S. C. Flock is 28.57 per cent. Over-all mortality appeared to be the collective effect of numerous causes. Under their analysis it was clear that a relatively small percentage of the ewes contributed a. high percentage of the total mortality. Certain individual ewes were found which consistently yeaned and. reared a single or a pair of twins each year, and made no contribution whatever to the mortality table. Some ewes consistently lost each successive lamb born to them. Some were very irregular in ability to yean and rear offspring each year. Likewise, certain indi- vidual rams might be getting progeny which showed high mortality or high livability. Many of the factors for livability or its converse, high infant mortality - are inheritable. Unfortunately, the identity of the genes responsible for inherited (3) mortality among the lmnbs and the mode and manner of their inheritance are not made clear by their analysis. Each death which occurred among the little lambs was clas- sified under two headings. One was called "Death-causing factors totally unrelated to possible inheritance,” and the other, "Death-causing factors which appear to be closely allied with inherited weakness." Under this grouping it was found that in Flock A, 75 per cent of the mortality 9. traced to factors which had the aspect of being inherent weakness, while 25 per cent of the mortality arose from factors totally unre- lated to any inheritance. In Flock B, the figure was 72 per cent related. to inherent weakness, with 28 per cent totally unrelated to inheritance. Assuming that the foregoing is a correct analysis the greatest hope for a reduction in the number of infant deaths among little lambs lies mainly and plainly in BREEDING. Angsis 2f Lamb Crop. The M. S. C. sheep flock consisted of six breeds, namely: Shropshire, Hampshire, Oxford, Rambouillst, Southdown and Cotswold, in the years 191+5 and 1911-6, and five breeds in 191W, without any Cotswold. The number of ewes in each breed varied considerably between ’4 and 1+0 in any one year, and between 20 and 110 in all the three years put together. These unequd numbers in the various breeds made some of the statistical calculations very discouraging and the interpretation of the results very cautious especially for significance test between breeds, as far as lamb mortality was concerned. However, it was found that a high mortality rate occurred in Cotswold, Oxford and Hampshire breeds than in ShrOpshire, Southdown and Rambouillet. During the three year period (191t5-191t7), the flock had 312 ewes, which dropped 14-83 lambs out of which only 337 survived. This gives a lamb crop of 108.01 per cent raised. In spite of the good care and management as well as good feeding, the lamb mortality is as high as 30.22 per cent, which draws the attention of every animal husbandmen to check it as soon as possible. 10. The age of lambs at the time of death varied up to 8 months. See Table II. The highest mortality occurred.within a fortnight after birth. As the age advanced, the death rate decreased. In other words, the lamb mortality is highest at, or soon after birth. However, about 95 per cent of the lambs died within 2 months of age. Only 8 out of 1&6 lambs died.bstwsen 2 and 8 months of age. Excluding these 8 lambs which were over 2 months old, the over-all mortality rate comes down from 30.22 per cent to 28.57 per cent which is still high. Tables I, II and III give the detailed figures of the number of ewes and lambs born and dead for the three years. The gist of the tables runs as follows: . Total number of owes a 312 Total number of lambs born a #83 Total number of lambs died - 1H6 Total number of lambs raised . 337 Therefore, Lambs dropped - l5h.87% Lambs raised - 108.01% Lamb mortality - 30.22% Lamb mortality 2 months old . 28.57% Rembouillet Southdown Cotswold Table'I ABALISIS OF LAMB GRGP. Tbtal Table‘II AGE OF LAMBS AND.MORTALITITRATE. ‘ moor 9 m.g‘or 6&8 at _ ol IIIIIHHHHHHIIII Premature Over 15 days Over 1 month Over 2 mo. ‘ to l -:'s to 1 month to 2 months to_8 mo. Hampshire Shropshire Oxford Rembouillet Southdown Cotswold Total Mortality $9 Lamb Mortality up to 1 month of age . 8h.93$ Lamb Mortality up to 2 months of age . 9h.52% l2. Ill .. l ill l l I‘ll I l I’ll- l|.llll ull‘l ll‘lllllllllllllll ll ll. .mmgmw.wm mUmU m20 ceased.“ vacuum s spa: managesm mo dead one «60:53 shop named 25 no we: named BEE ”E02 amen .o .m .2 Ummlm .o .m .2 d. asses _ «SH afloeasno — oomd daofimouflofl _ 8m mfloeaaao flea masses and? ope IJ. @102 page...” dhomuno JON: 6H0 fikofig Ill, .M $6.35 25. .msfideospsa cm we: chose .edgo sesame.“ mo hoaepsm esp “Kareem 3.3m Eno 93.0 mm dos; mafia “8&th dad manganese we can. .98 “sodas.“ defies .e :33 song?» Eon sand Sen d was mEB "H.602 ammmmm u 89% Hwamma 2m .88 — 8.5m .m .0 Sam .50 sesame H— nmaomm ommmm soamam 7|“— maid” memwm Time...“ ass I... i. ps3 chasmenem 5H season: IL .m. 237653 26. .omo munch mo emseoep some spon one: mamOHnopnm manage can ofie>o nosesoh .606209 :20 eonmfldom esp me Hem mm wcfieoosnnfi on mns_osesa .eHo mass m can: omsso 0:9 as annexes: yo coed seas: «oamnfim shop need can no me: mesa manna _ 882 mnemam 91. age ll, mmmwam one base ohsamosm 27m .0 .m .2 IL I .: MMmUHQMm "M802 27. DISCUSSION. From.the review of literature it has been noted that the foramen ovale can close before the navel cord is tied and while the ductus arteriosus is still patent. It is further said that the ductus can remain Open as long as three months of life, but not the foramen ovale. Closure of the ductus follows the closure of foramen ovale. On the contrary, the reverse has been observed, that is, while the ductus is closed the foramen ovale is found wide open at a varying period of one to 55 days. This condition is definitely something unusual, and it calls for further investigation. There is also an apparent cor— relation between patent foramen ovale and pneumonia which condition invariably results in.death. Patency of foramen ovale as late as 55 days of age cannot be considered normal unless it is proved so by further work on this line, which is possible in some of the slaughter houses where a large number of hearts of lambs of different ages would be eas- ily and cheaply accessible to investigation. Among the congenital abnormalities are found some freaks such as cyclOps, five-footed lamb, monstrosity, parrot-mouth and mummified foetus which may well be attributed to a lethal factor. The possible inherent causes account for 65.06 per cent of mortality which means that hereditary factor plays a greater part than environmental factor in.lamb mortality. This view is further evidenced by the fact that there is no significant year-to-year variation in the mortality rate. The belief that the practice of inbreeding might be responsible for the congenital defects has been proved inconclusive by the tracing of pedigrees, for you get almost the same results regardless of inbreeding or otherwise. 28. However, an intensive work on this line is yet to be done either to prove or disprove the point at issue. The survey of the flock shows that too many breeds with unequal numbers in the classes are not quite desirable to do any more work on this line than.what has already been dealt with herein. There seems to be breed difference in mortality rate. The Cotswold, Oxford and Hampshire breeds have all suffered twice as much as Shropshire, Southdown and.Rambouillet have. So, it seems possible to have a more profitable flock by keeping a.few selective breeds only. The sex dif- ference reveals the truth that males fall an easier victim.to nature than.females. The ewes that give birth to twins or triplets are more handicapped than those that lamb single. In general, this analysis mostly agrees with and slightly differs from.the report on "Dead.Lambs Do Tell Tales," by D. S. Bell, Ohio Agricultural EXperimant Station. The most startling thing about lamb mortality is that no one cause stands out to be mainly responsible for death; and the over-all mortality appears to be the collective effect of numerous causes. The present work shows that 65.06 per cent of the mortality is due to the possible inherent causes, which is not very far from Bell's figure which is 75 per cent of the mortality traced to inherent factors. According to his report, a relatively small percentage of the ewes contributed a.high percentage of the total mortality. This is true in the case of the.M. S. C. flock, because certain.ewes yeaned and.reared a single or pair of twins each year contributing nothing to the mortality table. For example, a.Hampshire ewe No. 73-39 has raised 10 lambs with- out any loss for a continuous period of 7 years from.l9hl to 1987. 29. However, there is great difficulty and danger, as well in selecting or culling ewes on this basis because some ewes are very irregular in their ability to yean and.rear offspring each year - one year a living lamb, the next year a dead one. A.few ewes give birth to twins successfully for two successive years and then, they start aborting or dropping weak lambs since third pregnancy, and vice versa. Individual rams might be getting progeny which show high mortality or its converse, high liva- bility which is inheritable, but it is not made clear by this analysis. However, the indications are that disposition to abort, yean stillaborns, drop deformed lambs, throw lambs of low vigour, and "get" ewes which show poor milk production, which lack mothering instinct, even to the case of consistently "over-laying" their lamb, have the aspect of being inherit- able defects (Bell, 1987). Granting that this analysis is correct, there is a great hope for reduction of lamb loss by proper breeding. SUMMARY AND CONCLUSIONS. l..A study'was made of the post-mortem.reports of lh6 dead lambs of six different breeds in the M. S. C. flock. 2. Patent foramen ovale as late as 55 days of age has been recorded in a.Hempshire ram lamb which invariably died of pneumonia. 3. Patency of foramen ovale in he per cent of the total mortality due to inherent causes is suggestive of some congenital abnormality in the foetal heart of lamb, which may predispose toward pneumonia. h. The lamb mortality rate in the M. S. C. flock is 30.22 per cent; and the possible inherent causes contribute to 65.06 per cent of that mortality. 5. There is no significant year-to-year variation in the mortality rate. 7. 10. 30. Although the lambs dropped is l5h.87 per cent, the lamb crop is only 108.01 per cent. Cotswold, Oxford and Hampshire breeds have each suffered almost double the loss experienced by Shropshire, Southdown or Rembouillet. More of ram.1ambs than of ewe lambs have significantly contributed to mortality rate; male mortality being 3h.32 per cent, and female mortality 23.69 per cent. Again, the loss is more in multiple births than in single births. Twin mortality is as high as 3h.95 per cent, and single mortality 20.12 per cent. ‘ Tracing of pedigrees of some lambs is inconclusive to show that the I practice of inbreeding has any effect on lamb mortality. If the lamb mortality rate is high and if the shepherding is good and the feed is adequate the indications are that the flockmaster has a breeding problem (Bell, 192+7). BIBLIOGRAPHY. Barclay, Franklin and Prichard. 1945. The Foetal Circulation. 45-143; 197-206. Charles C. Thomas Publisher, Springfield, Illinois. Bell, D. S. 1947. Dead Lambs Do Tell Tales. The Sheepman, Vol. XVII, March, No. 11; 446, 466. April, No. 12: 486. Scholl, L. B. 1939. A Summary of 700 Autofiiee on Sheep and Lambs. Jour. Amer. Vet. Med. Assn., 94: 665-664. - Smith, C. A. 1945. The Physiology of the New-Born Infant. 65-75. Charles C. Thomas Publisher, Springfield, Illinois. Hindle, W. F. 1940. The Physiology of the Foetus. 20-47. W. B. Saunders Company, Philadelphia. Winters, L. M. 1944. Animal Breeding. 5rd Ed. 119-129. John Wiley and Sons, New York.