Long-term performance and health cows experimentally exposed to polybrominated biphenyls

Fifteen Holstein cows were studied for up to 15 00 days to determine whether exposure to polybrominated biphenyls produced latent or subtle toxicosis not evident in previous acute or short studies. Animals for these long studies came from three groups given 0, .25, or 250 mg of fireMaster BP-6 per day for 60 days in 1975. Another group that received 250 mg of BP-6 for 180 or 202 days in 1976 also was studied. Individual animals were in their second, third, or fourth lactations. Milk production was not different among experimental groups, and mature body weights were similar. Increases in the amount or duration of exposure did not increase number of infections, dysfunctions, or general injuries. Exposure to 250 mg/day for 60, 180, or 202 days increased frequencies of reproductive disorders at parturition, particularly related to and following a high incidence of dystocia. A contributing factor to dystocia was larger birth weights of calves from cows exposed to 250 mg daily as compared to calves from cows exposed to 0 or .25 mg polybrominated biphenyls. Although reproductive dysfunctions required more veterinary care, numbers of services per conception were not different among groups.