Intrauterine growth retardation as a cause of perinatal mortality in Japanese black beef calves

Perinatal death is one of the major causes of calf mortality in Japanese Bl ack beef herds. A series of experiments mere carried out to determine cause s of perinatal calf mortality in a region of northern Japan. hn aetiologica l survey revealed that the incidence of perinatal mortality in 6475 calves was 4.5 % and the majority of neonatal deaths were caused by weak calf synd rome. The weak calves delivered after a normal gestation period had a signi ficantly lower body weight at birth than normal calves (P < 0.01), indicati ng growth retardation in the uterus during pregnancy. Haematological and hi stopathological examinations showed that the weak calves had anaemia charac terized by a significant decrease of blood cell values and bone marrow hypo function. The anaemia due to bone marrow hypofunction presumably caused int rauterine growth retardation of the foetus. Dams delivering the weak calves showed significantly lower serum concentrations of estrone sulphate during late pregnancy than those with normal calves (P < 0.01), indicating foeto- placental dysfunction as a possible cause of growth retardation. Effects of sires as well as the maternal family on the incidence of neonatal death an d on the rate of weak calves in dead neonates were found in the survey. Int rauterine growth retardation associated with anaemia may be the most import ant cause of weak calf syndrome in Japanese Black beef calves. The bull and maternal family may also have an influence on the incidence of neonatal de ath.