The effects of breed, breeding system and other factors on lamb mortality: 1. Causes of death and effects on the incidence of losses

Abstract

The incidence of lamb mortality from birth to 8 months of age has been studied over a 6-year period in an upland, grassland flock of sheep comprising the Scottish Blackface, Cheviot and Welsh Mountain breeds and the crosses among these breeds. Each breed and cross-bred type was maintained at varying levels of inbreeding. Approximately half the lambs which died were stillborn or dead on the day of birth, nearly 40 % died thereafter but before weaning and about 10% after weaning.Post-mortem examinations on 586 of the 632 lambs which died from among the 2453 born attributed death on average to two causes per lamb. Approximately 11 % of the causes were stillbirths or delayed births; 11 % were cases of dystokia; congenital defects of various types accounted for about 10% of the causes; 25% made reference to weakly lamb, exposure or starvation; 14% to infectious diseases and 16% to noninfectious diseases. The extent to which causes of death occur together is examined.Breeds differed in mortality rate with the Welsh the lowest and Cheviot the highest. Cross-breds were better than the average of the pure breeds but this advantage emerged only in the period between 3 days and. 6 weeks of age. Inbreeding, both of dam and of lamb, increased mortality. Lambs from dams which were crosses of inbred lines had the best survival. Litter size, type of rearing, parity of dam, sex of lamb and birth weight also had significant effects on mortality rate. INTRODUCTION describe breed differences in relation to specific causes of death. Many studies of sheep flock performance provideThe present study was initiated primarily with information on the incidence of lamb mortality in the latter end in view: to document the lamb different countries and farming circumstances and mortality rate in relation to three breeds and their at different periods between birth and weaning, crosses kept together as a single flock and also subSome describe the effect of factors such as number jected to intense inbreeding. The effects of breed, of lambs born, parity, management, nutrition and cross-breeding and inbreeding were further studied other environmental variables and a smaller number m relation to the causes of death as identified at of papers present information on causes of death, post-mortem examination. Other factors affecting Although these reports encompass many breeds and variation in overall mortality and the incidence of crosses of sheep, only a few can be interpreted as different causes are also examined, showing whether genetic variation contributes sigAn early finding in this flock was that both breed nificantly to lamb survival and even fewer papers a n d breeding system affected overall lamb mortality

Risk factors associated with lambing traits

“…The greater lamb mortality recorded in purebred lambs compared with crossbred lamb corroborate the conclusions of Wiener et al (1983). The difference in lamb mortality between purebred and crossbred lambs in the present study may be partly explained by the influence of heterosis on lamb viability, and subsequently on lamb mortality (Gama et al, 1991).…”

“…A combination of management and environmental factors has previously been documented to be associated with lambing difficulty and lamb mortality in the United Kingdom (Wiener et al, 1983;Dwyer et al, 1996), New Zealand (Morris et al, 2000;EverettHincks et al, 2005), Australia (Geenty et al, 2014) and the United States (Gama et al, 1991;Southey et al, 2004) sheep populations. No study has to date examined the association between lambing difficulty and mortality and risk factors in a series of simple regression models and multiple regression models across a diverse sheep population.…”

“…Lambing dystocia alone has been reported to account for up to 11% of lamb mortality (Wiener et al, 1983). Moreover, to date, no study has examined the risk factors that influence lambing difficulty and lamb mortality in a series of simple and multiple regression models across a large number of purebred and crossbred animals on commercial farms.…”

Early neonatal lamb mortality: postmortem findings

“…In flocks practicing outdoor lambing, neonatal mortality rates ranging from 6% to 14% have been reported (Wiener et al, 1983;Cloete et al, 1993;Everett-Hincks and Dodds, 2008). Exposure to adverse weather conditions and insufficient intake of colostrum are important risk factors for neonatal mortality, and hypothermia and starvation were main causes of death in these studies.…”

Threshold model analysis of lamb survivability in Romney sheep

“…In order for the lamb to survive, it must have the desire and ability to regulate temperature (Hight & Jury 1970), stand, and obtain nutrition from its dam within minutes of birth (Cloete & Scholtz 1998). Throughout the period from birth to weaning, the lamb must imprint with its dam (Alexander 1961), compete with siblings or other lambs for the dam's milk, start using forage, and exhibit disease resistance (Wiener et al 1983). The maternal component of lamb survivability encompasses the ewe's ability to provide adequate uterine conditions during gestation, seeking shelter at birth and during subsequent bad weather, bonding with the lamb(s) (Cloete et al 2002), passing on antibodies for disease resistance through colostrum (Stormont 1972), maintaining freedom from udder abnormalities, and generating sufficient milk (Moule 1954).…”