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The effects of maternal age and birth weight on survival of twin lambs has been studied in a Blackface and a Welsh Mountain flock. The time of death was also investigated for both singles and twins.Twin mortality was higher than mortality of singles, mainly due to the lower average birth weight of twins. Twin mortality declined with increasing birth weight although it showed a tendency to increase at the top of the scale. Weight for weight, mortality was similar for singles and twins. Twin mortality declined with increasing age of ewe in a very similar pattern to single mortality.Lamb mortality was heavy at birth and during the first 14 days of life with only 30% of the mortality occurring after this age. Approximately 12% of the dead lambs were stillborn. Among singles a similar proportion died as a result of difficult births, but this cause of mortality was rare in twins.Stillbirth mortality rates were very high for very small birth weights and declined with increasing weight of lamb. Difficult births, on the other hand, increased with increasing birth weight. The association of birth weight with mortality was particularly important in the first 14 days of life but thereafter its significance was less.Although mortality in lambs of younger ewes was heavier than that of older ewes, similar causes of death operated. Younger ewes, however, having lower birth weights tended to have more stillbirths but few losses due to difficult lambings.

An analysis of the breeding performance of sorne 11,258 sheep, mostly Corriedale, over aperiod of 15 years in relation to liveweight at mating has been made, yielding the following observations:- (i) Ewe and lamb mortality, 3.8 per cent and 12.0 per cent respectively, are independent of liveweight of the ewe, except at liveweights below 90–100 lb. (ii) Barrenness (mean 6 per cent) is relatively independent of liveweight above approximately 90–100 lb but below this critical weight barren (iii) Twinning increases approximately linearly with increasing liveweight at a rate of the order of 6 per cent per 10 lb. (iv) The lower breeding performance of 2-tooth ewes in comparisonwith older ewes can be explained almost entirely in terms of liveweight at mating. The relative significance of liveweight and flushing as factors influencing lambing percentage are discussed.

SUMMARYHaemoglobin types of two Indian breeds of sheep were related to ram and ewe fertility and lamb mortality. Rams with Hb B type had a significantly higher number of lambs born to ewes mated to them. Ewe fertility and lamb mortality were better, but not significantly so, in animals with Hb B type.

Lamb mortality is a serious source of economic loss to the sheep industry. Surveys have shown that up to 50% of the post-natal losses can be due either directly or indirectly to cold exposure. This thesis examines various ways of improving thermoregulation in the newborn lamb. Emphasis was placed on the need to develop methods which required little or no capital expenditure. This was essential if the most promising techniques were to be adopted in the less favoured hill environments. The effectiveness of the various treatments was measured by subjecting each newborn lamb to a standard cold exposure in a progressively cooled water bath. Various components of heat production and heat loss were recorded during this test. The cold resistance of each lamb was defined as the time taken for rectal temperature to fall by approximately 4C. The capacity for non-shivering thermogenesis (NST) was also measured in some lambs by recording the calorigenic response to noradrenaline administration at a therinoneutral temperature. Shearing of the pregnant ewe 4 weeks before parturition increased the cold resistance of the newborn lambs. Components of both heat production and heat loss were influenced by this treatment. Short periods of acute cold exposure imposed daily for the last 12 days of pregnancy enhanced NST in the newborn lamb. Further work showed that all these results were influenced by ewe age, breed, foetal number and year effects. The implications of this, and possible mechanisms, were discussed. Genetic selection for cold resistance in Scottish Blackface lambs started at ABRO in 1980. Preliminary results of this experiment are reported here. The response was asymmetrical. Selection for high cold resistance produced considerably more progress than selection for low cold resistance. Heritability of cold resistance estimated from line divergence was 0.17+0.09. Heritability for increasing cold resistance was 0.27+0.13 and for decreasing cold resistance it was 0.01+0.16. The large number of lambs tested during this experiment (594) allowed a detailed investigation of various components which influenced water bath performance. Single lambs had a greater we ight-specif ic heat production and reduced heat loss compared to twins. Female lambs were better able to thermoregulate than males. Cold resistance tended to decline with age but increase with liveweight. The genetic and phenotypic relationships between cold resistance and components of heat production and heat loss were analysed. The implications of these findings with regard to thermoregulation and hence lamb mortality in the field situation were discussed.

The incidence and effect on reproduction of a constriction of the vagina was studied in 12 maiden merino flocks on 5 commercial properties in Western Australia. The overall incidence of the constriction was 11% with a range of from 2% to 27%. Ewes with a constriction of the vagina exhibited inferior reproductive capacity; fewer ewes lambed and of those that did fewer reared their lambs. A higher lamb mortality was recorded in lambs born to such ewes.

Lamb mortality to weaning age was compared in Merino flocks selectively bred from maternal ancestors with high or low lifetime rearing ability. The High Efficiency (HE) flock comprised the descendants of ewes that had reared lambs on 3 or all occasions from 4 rearing opportunities. The Low Efficiency (LE) flock comprised descendants of ewes that had failed to rear any progeny on 2, 3 or all occasions from 4 rearing opportunities. During the first 3 years of testing the response to selection the mean mortality to weaning among HE single lambs was 19.5% of lambs born compared with 32.3% in the LE flock (p less than 0.001). Mean mortality of twin lambs in the HE flock was 21.5% compared to 36.3% in the LE flock (p less than 0.01). In the HE flock significantly fewer single lambs died during and within 3h of birth and significantly fewer twins died during birth and shortly thereafter, and between 3h and 2 days of age. The viability of LE singles and twins may have been lower overall as the mortality rate in most periods was higher than that of their HE counterparts. The results highlighted the major impact of intrinsic maternal and, or foetal defects on lamb survival. It was concluded that rearing ability was heritable, and that selection for rearing ability offers excellent prospects for alleviating the hitherto intractable problem of high perinatal lamb mortality.

Vibrionic abortion was diagnosed in sheep on 48 occasions between 1963-65 and 3 of these were associated with other major abortion pathogens. The outbreaks were scattered throughout the agricultural area of Western Australia. Time-of-death of 91 infected lambs was: ante-parturient death 50.5%, parturient death 13.2% and post-parturient death 36.3% (deaths occurring immediately after death 28.6%, deaths delayed after death 2.2%, and late post-parturient death 5.5%). The majority of lambs had gross lesions, mainly subcutaneous oedema and excess fluid and fibrin in the serous cavities. The characteristic gross liver foci were present in 37.4% of the infected lambs examined. Seven lambs with signs of starvation had liver lesions: necrotic foci (6) and hepatomegaly (1); Campylobacter fetus subsp. intestinalis was recovered from the liver and/or gall bladder of each of the lambs. Epizootiological observations were reported including outbreaks under hot semi-arid conditions.

Three factors were associated with lamb neonatal mortality: birthweight (P

Stevens, D., Alexander, G. and Lynch, J.J., 1982. Lamb mortality due to inadequate care of twins by Merino ewes. Appl. Anim. Ethol., 8: 243–252. One hundred and three fine-woolled Merino ewes and their twin lambs in four 12-ha paddocks, carrying 12.5 sheep per ha, were observed during daylight for 2—4 days immediately following parturition. Fifty-one ewes became permanently separated from one twin due to the ewe moving and leaving the lamb behind, mostly on the day of birth; the ewes appeared unconcerned if followed by only one lamb. Only two ewes became separated from both lambs. Human interference appeared to play only a minor role in these separations. Low vigour of one twin, as assessed within several hours of birth, usually resulted in its early separation from the ewe, but more than half of the lambs separated from the ewes were vigorous and mobile. Regardless of separation, all lambs of low vigour died. In this flock, the inability of the ewes to keep twins together, and maintain contact with both, contributed largely to the higher mortality in the twin lambs than in singles in the same birth-weight ranges; overall, 37.4% of twins died compared with 9.6% of singles. These figures indicate there could be a problem of high mortality in twin lambs from fine-wool Merino flocks under commercial conditions where lambing takes place in paddocks that are usually well in excess of 12 ha.

Many commercial sheep farmers do not record either the extent or the causes of their lamb losses but this information is essential if losses are to be reduced in the future. The major causes of death in newborn lambs are reviewed together with the common predisposing factors. The development and practical application of a simple system for recording lamb deaths is described. It is concluded that the application of this type of system, initiated, supervised and interpreted by the farmer9s own veterinary surgeon, would indicate how to reduce the losses of lambs and would be a useful component of any flock health scheme.

Three-hundred mature Panama-type range ewes were mated to Clun Forest, Dorset, Border Leicester, Polypay and Suffolk rams during the 1979 and 1980 breeding seasons. Sire breed and ram within breed effects on lamb growth, ewe reproduction, spermatozoan midpiece length (MPL) and midpiece length coefficient of variation (MPLCV) were examined. Associations among MPL and MPLCV and economically important traits also were assessed. Suffolk-sired lambs weighted .18, 2.0 and 1.5 kg more, at birth, weaning and post-weaning, respectively, than the average of all groups. Dorset-sired lambs had the lightest postweaning weight. Variation was greatest among Suffolk rams for average weaning and postweaning weights of their progeny. The Border Leicester breed had the least among ram variation for progeny weaning weight; while variation among Dorset rams was least for progeny postweaning weight. Fertility (ewes lambing/ewe exposed) and prolificacy (lambs born/ewe lambing) of the rams' mates were not influenced significantly by sire breed. Lamb mortality also was not influenced by breed of sire nor by rams within a breed. For variation in MPL, 26.4% was due to the breed effect (P less than or equal to .01) and 21.6% was attributable to ram variation within a breed (P less than or equal to .01). Clun Forest rams had the longest average MPL and greatest MPLCV, while Dorsets had the shortest MPL and smallest MPLCV. There were no important associations between either MPL or MPLCV and any of the economic traits.

The reproductive performance of the Y'ankasa sheep of Nigeria was studied to determine any seasonal effects on their breeding pattern. The study also aimed at documenting the reproductive performance levels of these animals as a basis for evaluating the results of any breeding improvement program in Nigeria using indigenous or exotic breeds of sheep. The study shows that this breed of sheep is a year-round breeder although some months favor lambing more than others. The age at first lambing and the lambing interval for these animals are 15.5 months and 9.7 months respectively. For 1975, the conception and lambing rates were 87.8% and 139% respectively. The rates for 1976 were 91% and 148%. Seventy-seven percent of the lambing were singles and the rest twins. The sex ratio, number of females per 100 lambs, was 49%. Lamb mortality rate up to 3 months of age was 12.0%. The lambs in our study grew very slowly, gaining only 15 kg in a 9-month period. By 10 months of age these lambs wieghed only 20 kg.

Arnold, G.W. and Morgan, P.D., 1975. Behaviour of the ewe and lamb at lambing and its relationship to lamb mortality. Appl. Anim. Ethol., 2: 25–46. A number of behavioural traits associated with the maternal instinct of sheep were studied under paddock conditions over a range of breeds, age, climate, nutrition and locations in five lambings in south Western and north Western Australia. There was very considerable variation between ewes in any group in the occurrence and timing of each trait. There were few differences due to breed, age of ewe, nutrition, climate or location in the behaviour of the ewe before and during parturition. Nearly all the differences that occurred were in the frequency of pawing the ground before and during labour. Fewer Southdowns and Merinos pawed the ground than ewes of other breeds. Also this trait occurred more in summer than in winter in south Western Australia, and less here than in north Western Australia. The behaviour of the ewe during the post partum period was highly predictable. She normally stood and commenced cleaning within 1 min of birth. Cleaning commenced at the head and progressed down the body. Desertions and other forms of aberrant behaviour were uncommon. There were no biologically significant differences in length of labour, time from birth to stand and time from stand to first drink due to breed, age, pre-lambing nutrition, climatic conditions or location. Second-born twins were delivered after a significantly shorter labour than first-born twins. In one series of observations twins took longer to drink than singles. Type of birth did not influence the time taken for the lamb to stand. Rectal temperature three hours after birth dropped significantly when rainfall exceeded 2 mm during the 3 h. Lamb mortality increased significantly in wet weather in winter and most lambs which died more than 3 h after birth had a depressed rectal temperature at 3 h. The ewes of lambs which died after standing tended to have longer than average labour. Poor maternal behaviour per se was the cause of 16% of lamb deaths and failure of the lamb to drink after standing caused 23% of lamb deaths in winter in south Western Australia. In summer in both environments heat stress was the primary cause of lamb deaths.

Extract Perinatal losses in farm livestock are high and yet they have received little systematic study. During an extensive survey of over 8,000 lamb deaths occurring before, during or within seven days of birth (perinatal mortality), autopsy and recording methods have been evolved which could well serve as bases for similar studies.

The hypothesis tested in this experiment was that the effects of gastrointestinal nematodes (GIN) on growth of meat-breed lambs would be absent during the suckling period and greatest after weaning. The experiment was a single factor design conducted on five farms over 2012–2014, using meat-breed lambs (Poll Dorset × Border Leicester/Merino), which were either GIN-suppressed (SUP) or not (NSUP). The experiment commenced at lamb marking and continued for 5 months. SUP lambs were serially treated with short- and long-acting anthelmintics. NSUP lambs were not treated before weaning and at weaning received a short-acting multi-active drench with subsequent treatments varying between farms. Worm egg count (WEC) of NSUP lambs were significantly higher (P < 0.0001) than SUP lambs at weaning (1170 and 10 epg) and thereafter (P < 0.0001) reaching 920 epg 2 months after weaning. Haemonchus contortus was the predominant species present in NSUP lambs with smaller contributions from Trichostrongylus spp. There was no effect of GIN control on lamb growth during the pre-weaning period (SUP 17.2 kg vs NSUP 17.0 kg, P = 0.093), whereas GIN reduced growth of lambs by 0.5 kg (SUP 7.1 kg vs NSUP 6.6 kg, P = 0.002) in the last month of observation. There was no effect of GIN control on lamb mortality. GIN did not affect growth of suckling meat-breed lambs despite high WEC at weaning indicating resilience to GIN infection in lambs growing at 200 g/day. In contrast, post-weaning growth was reduced by GIN infection, despite effective treatment at weaning and movement to GIN ‘safe’ pastures. The susceptibility of weaned lambs to the effects of GIN infection highlights the importance of effective control measures at this time.

An outbreak of congenital goitre associated with minimal thyroid enlargement resulted in a high level of lamb mortality (36.1 per cent) in a flock in northern Tasmania. Palpation was shown to be a valid means of assessing thyroid gland size and a significant linear relationship between thyroid size and lamb mortality was demonstrated (P < 0.01). Although the overall difference in mortality rate between normal and goitrous lambs was significant this was confined to the middle of the birth weight range; at either end of the range the normal and goitrous lambs experienced similar levels of mortality. Goitrous lambs died earlier and had less chance of walking or metabolising their fat reserves than their normal counterparts. There was no effect of sex or type of birth (single or multiple) on incidence of goitre. In most of the goitrous lambs that survived, thyroid size had regressed to normal in about six weeks.

A bighorn sheep (Ovis canadensis) herd was observed in the Sangre de Cristo Mountains of Colorado during the spring, summer, and fall of 1969 and the summer and fall of 1970. June ewe-lamb ratios were 100:83 in 1969 and 100:72 in 1970. High late summer lamb mortality occurred during both years, with the ewe-lamb ratio being 100:17 by September 1969, and 100:22 by September 1970. Lamb mortality resulting from predation or accidents was not found to be a factor. Disease, possibly enhanced by inclement weather, was believed to be a significant factor in lamb mortality. Two lambs were collected in 1970, and both displayed a verminous pneumonia of lungworm (Protostrongylus stilesi) origin and a broncho-pneumonia of probable bacterial origin. J. WILDL. MANAGE. 38(4):771-774 Many of the Rocky Mountain bighorn sheep herds in Colorado are presently static or decreasing in size (Bear and Jones 1973). As the Sangre de Cristo herd apparently has declined since the mid-1950's, a study to investigate this herd reduction was initiated in 1969. The objectives of the study, completed in 1970, were to determine sheep distribution, lamb birth rate, survival, and mortality. We thank D. Post and C. Hibler, Colorado State University, for their guidance. D. Riggs and D. Crane, Colorado Division of Wildlife, and J. Landen of Alamosa, Colorado, assisted in field research.

Three systems of lambing management were compared at Trangie in Central Western New South Wales. A supervised system involving daily drifting of ewes through a series of small paddocks was first compared with an unsupervised system in which ewes were set-stocked in a single large paddock (A) and later, an unsupervised system in which ewes were set-stocked in sub-flocks according to their expected date of lambing (B). Lamb loss associated with the management of marking and mulesing proved to be an important factor in the comparison. The introduction of unsupervised system (B) was associated with a reduction in losses after marking compared with the supervised system. Lamb loss prior to marking was lowest in the supervised system. Of the three systems, unsupervised system (B) is considered the most suitable for areas in which environmental conditions during lambing are not harsh.

Merino flocks lambing in either autumn or winter in south-eastern South Australia showed no consistent differences in reproductive performance over a five-year period. The percentage of ewes that lambed, the level of twin births, and the lamb mortality rates varied in their relative contribution to the final result in any one season. For each reproductive factor measured the difference between the flocks varied from year to year in magnitude and sign. Lambs born in the winter had higher birth weights and better early growth rates, but liveweight during their first summer period was generally less than that of autumn born lambs. Survival rates in both groups were similar.

Statistics are presented from a Peppin Merino parent stud on seasonal variation in flock fertility, differences in fertility between rams of various ages, lamb mortality, age composition of the ram pool, and the differential we of rams of various ages. Variation of the percentage of lambs born to ewes served was largely due to seasonal differences in the proportion of ewes (2.5 per cent to 26.5 per cent) with twins. The majority (about 7 per cent) of lamb deaths up to 24 hours after birth was due to natural causes. Total lamb mortality up to 21 days of age was 13 per cent of the number of lambs born. Male lamb mortality up to 24 hours, including lambs born dead, was higher than female mortality (17 per cent u. 6 per cent). Age composition of the ram pool and ram wastage indicated a replacement rate of about 25 per cent. Average age of rams was 4.4 years at the time of birth of their offspring. Ram fertility, assessed as the percentage of ewes lambing to ewes mated, was 55 per cent for two year old, 70 per cent for five year old, and 59 per cent for nine year old rams. From a total of 27 to 37 rams in we each year, 10 favoured rams sired 52 per cent to 70 per cent of lambs alive at 24 hours. These favoured rams were also above average age (5.1 years v. 4.4 years). Thus, favoured sires contribute more heavily to the future flock genotype than other sires; firstly because they have more offspring, and secondly, became pedigree records provide the basis for additional favouritism towards their offspring, especially in the choice of stud ram replacements. This operational pattern has the two-fold disadvantage of increasing the generation intervals relevant to flock replacements and of inefficient exploitation of genetic gains already, made. If, as we believe, this operational pattern is currently typical of the foremost studs of the Merino industry, if is a matter of some concern with respect to the implementation of genetic improvement programmes and the progress expected from them.Where present procedures follow such a pattern thy should be largely reversed so as to use a higher proportion of young rams and to mate them to a much larger proportion of the ewe flock.

Surveys of neonatal lamb mortality show that neither disease nor predation is reponsible for most of the losses, although in certain flocks these factors may cause severe damage. Nearly half of the lambs are starving at death and this suggests a breakdown in the mother-offspring relationship. The pertinent aspects of ewe and lamb behaviour and physiology are discussed and the predisposing conditions for predation are defined as: (1) faulty nutrition of the ewe during pregnancy, resulting in prolonged labour; (2) climatic stress during and after parturition. The species involved in lamb predation and carrion feeding are discussed in relation to the role played by these animals in neonatal lamb mortality. The need to distinguish between the predation of healthy lambs, the predation of sick and weakly lambs, and the eating of carrion is emphasized. Wounds made by Australian carnivorous animals, on both live and dead lambs, are described and a key to lamb-wound identification included. Appendix I describes the technique of lamb autopsy and the assessment of lamb viability. Appendix II gives an example of the use of this method in the analysis of predation in two flocks. Appendix III discusses the terminology relevant to predators and predation.