Perinatal lamb mortality - its investigation, causes and control

Abstract

Methods of investigating perinatal loss in grazing sheep flocks are reviewed and evaluated. The "wet-dry" method is the simplest method for assessing minimal prevalence, whereas the differences between the numbers of single and twin foetuses present at ultrasonic determination of litter size during pregnancy, and the numbers of single and twin lambs present at lamb-marking, is the most precise. The veterinary investigation of field mortality involves full autopsy of a representative sample of dead lambs, a history of prenatal nutrition, disease and husbandry, as well as a qualitative estimate of weather conditions over the period of lamb collection. Pathological processes may be identified in over 95% of deaths and the specific cause determined in about 75% of deaths. The identification of the specific causes in the remainder of deaths, all classified as the starvation-mismothering-exposure (SME) complex, requires intensive, costly, on-site observation, and physiological and biochemical assessment. The probable causes of these deaths include prenatal physiological handicaps resulting from placental insufficiency, aberrant parent-offspring behaviour, management-induced mismothering, misadventure, inadequate milk supply or teat and udder abnormalities, and cold-induced starvation. The gross pathology and pathophysiology of birth stress and the SME complex, which are associated with at least 80% of mortality, are summarised. Birth injury to the foetal central nervous system, characterised by cranial and spinal meningeal haemorrhage is exclusive to parturient deaths and the SME complex. Observed flock prevalences range from 81% to 100% in parturient deaths, and 20% to 57% in the SME complex. The high total prevalence and experimental evidence, indicate the major causal role of birth stress in the pathogenesis of these entities. Lethal congenital malformations, infections (both congenital and acquired after birth), trace element deficiencies and predation are reviewed as minor causes. The new understanding of the pathogenesis of perinatal lamb mortality, recognises the heritable nature of birth mass, maternal pelvic dimensions, parent-offspring behaviour, and the resistance of neonates to cold. Control measures need to incorporate selection for maternal rearing ability, further refinement of prenatal nutritional management of twin-bearing ewes, disease control, provision of shelter for lambing flocks, and avoidance of husbandry: practices which frustrate innate parent-offspring behaviour. A selection programme is summarised.

Evaluation of the Brix refractometer as an on‐farm tool for the detection of passive transfer of immunity in dairy calves

“…The device has the potential for other uses in the livestock industries; for example in the bobby calf industry to determine the health status of a calf by identifying immunity levels before deciding to sell or purchase the animal. It may also have implications in the beef and lamb industries, as mismothering and neonatal deaths contribute to significant losses in these industries …”

Urea supplementation effects on the utilization of low‐quality forage and lamb production in patagonian rangelands

“…Higher liveweight gains during this period result in a higher birth weight of lambs (Shelton, 1964;Milchalk and Saville, 1979;Scales et al, 1986;Rattray, 1992;Haughey, 1993) and greater milk production in ewes (Hussein and Jordan, 1990;Holstet al, 1992). Both higher birth weight and greater milk production will reduce perinatal mortality (Shelton, 1964;Milchalk and Saville, 1979;Scales et al, 1986;Rattray, 1992;Haughey, 1993). A higher birth weight and/or greater milk production of supplemented ewes would explain the higher live weight and survival rate at 8 weeks of age in the supplemented lambs.…”

Parity and litter size effects on maternal behavior of Small Tail Han sheep in China

“…It is reported that the majority of lamb deaths occur in the lactation period from starvation, mis‐mothering and exposure (Dalton et al . ; Haughey ), and adverse behavior of ewes (Nowak ). Maternal behavior in Small Tail Han sheep has not been studied in any great detail.…”