Interrelationships between ambient temperature, age at calving, postpartum reproductive events and reproductive performance in dairy cows: a path analysis

Path analysis was used to determine the interrelationships between ambient temperature, age at calving, postpartum reproductive events and reproductive performance in dairy cows. The data used in the analysis were collected on 226 Holstein-Friesian cows calving in a commercial dairy herd during a 17 month period (May 1, 1981 to October 1, 1982). The data were obtained from a double blind study evaluating the effects of gonadotrophin releasing hormone and cloprostenol in postpartum cows. Rectal palpation to assess uterine involution and ovarian activity was performed on each cow on days 15, 24 and 28 postpartum. At the same time, blood samples were collected for subsequent progesterone assay. Data were recorded on the occurrence of reproductive diseases and events from the time of parturition until the diagnosis of pregnancy or until the cow left the herd in the case of culled cows. There was an increase in the incidence of retained placenta, in the percentage of cows with abnormal vaginal discharge in the early postpartum period as well as a delay in uterine involution during the winter months. In addition, cows calving during the winter had prolonged intervals to first estrus, first service and conception compared to cows calving during the summer. (Cows calving during the warmest months, on average, were seen in estrus 24 days sooner, received first service 42 days sooner and conceived 27 days sooner than cows calving during the coldest months of the year).