A Study of Perinatal Mortality of Lambs from the Oberon, Orange and Monaro Districts of N.s.w

In this paper perinatal mortality is defined as those deaths occurring before, during or within seven days of lambing. Extensive surveys on abortion and stillbirths in sheep from several flocks have been reported from Great Britain (Sellers and Leech 1955; Leech and Sellers 1959; Watson 1962cr), from U.S.A. (Bell 1944, 1947), from New Zealand (McFarlane 1955; Hartley and Boyes 1955, 1964; Hickey 1960, 1963), and from Australia (Moule 1954), revealing an average perinatal mortality ranging from 2% to 21% . Considerable information is also available on perinatal mortality and possible causes of death in individual lambs and flocks (Wallace 1949; Venkatachalam et al. 1949; Pugh 1954; Alexander, McCance and Watson 1955; Alexander, Peterson and Watson 1959; Safford and Hoversland 1960; Vetter, Norton and Garrigus 1960; Watson and Elder 1961). These comprehensive investigations have incriminated a multitude of factors as contributing to lamb mortality, particularly dystocia, predation, infection, nutritional and environmental stress, and genetic factors. Some aspects of nutritional stress in pregnant ewes as a factor in lamb mortality are well documented. Ingestion of poisonous plants, pregnancy toxaemia, copper deficiency, iodine deficiency, Vitamin A deficiency and selenium responsive myopathy have all been shown to act as potent predisposing factors in perinatal lamb losses under certain circumstances. Other known non-infectious causes of mortality include muscular dystrophy of unknown aetiology (Stamp 1960), congenital deformities, dystocia, climatic stress, predation and the presence of unsound udders in dams. The oral administration of anthelmintics and the development of cutaneous myiasis in ewes heavy in lamb may also cause perinatal losses. The infective agents responsible for neonatal mortality in lambs have been adequately reviewed by Watson (1962b, 1962~); micro-organisms demonstrated in or isolated from aborted and stillborn foeti include Brclcella abor~us, Br. Melitensis, Br. ovis, Corynebgcterium pyogenes, Esch’erichia coli, Fusiformis frugilis, Lept!ospira spp., Listeria monocytogenes, Pasteurella spp-, Salmonella spp,, Vibrio fetus, unidentified Streptococci, unclassified gram negative and gram positive bacilli, a member of the psittacosis -1ymphogranuloma group, Coxiella burneti and Toxoplasma gondii. Tick-borne fever, Wesselbron virus and the virus of Rift Valley Fever have also been incriminated as a cause of abortion in ewes. Post natal