RISK-FACTORS FOR PERINATAL AND POSTNATAL MORTALITY IN LAMBS

Factors associated with preweaning mortality in lambs were identified by developing risk profiles with logistic regressions for perinatal an d postnatal mortality, Compared with heavy lambs, lambs of low birth w eight had almost twice the risk of perinatal mortality (odds ratio [OR ]=1.9) and lambs of average weight had a slightly lower risk (OR=0.7). Two of four lambing location categories affected perinatal mortality, with lambs born at unmonitored areas at greatest risk (OR=2.7). Multi ple births increased the risk of perinatal mortality (OR=1.5), especia lly among Targhee lambs (OR=4.0). Breed variations in perinatal mortal ity were significant in Suffolk lambs (OR=1.9) and Booroola Rambouille t lambs (OR=2.1). Lambs born weak had an increased risk of postnatal m ortality while strong lambs had a decreased risk (OR=3.7 and 0.6, resp ectively) if the dam had an adequate milk supply, Poor milk supply inc reased the risk of postnatal mortality for lambs of average vigour (OR =3.3), but did not change the risk for weak or strong lambs. Male lamb s castrated at 30 days of age were at less risk of postnatal mortality (OR=0.3) than females. There were slight increases in the risk of pos tnatal mortality for intact males (OR=1.3), low birth weight lambs (OR =1.6), and lambs born in sheds (OR=1.3). Suffolk lambs (OR=1.8) and Ta rghee lambs (OR=1.6) had a higher risk of postweaning mortality.