Effects of post partum stress on reproductive function in dairy cattle

The objectives of the present study were to investigate the effects of condition of parturition, body condition at calving, puerperal complications, milk yield, and parity on the postpartum adrenocortical and pituitary functions, ovarian activity and uterine involution in dairy cows. Adrenocorticotropic hormone (ACTH) challenge tests for adrenocortical function at 8 and 22 days postpartum and gonadotropin releasing hormone (GnRH) challenge tests for pituitary function at 7 and 21 days postpartum were conducted in 44 Holstein-Friesian dairy cows. Ovarian function, particularly the interval to first ovulation, was evaluated by three times weekly milk progesterone test. Uterine involution within 30 days postpartum was evaluated by weekly rectal palpation and ultrasonographic examination. Varying influence of condition of parturition, body condition at calving, puerperal complications, milk yield and parity on postpartum adrenocortical and pituitary function, ovarian activity, and uterine involution were observed. In general, adrenocortical function at 8 days postpartum was apparently enhanced by dystocia, poor body condition at calving, postpartum reproductive disorders such as retained placenta and endometritis, high milk yield, and increased parity. Postpartum metabolic disorders combined with reproductive disorders appeared to be associated with depressed adrenocortical function. In association with enhanced adrenocortical function, pituitary function tended to be depressed at 7 days postpartum in cases of dystocia, poor condition at calving, high milk yield and increased parity. The resumption of ovarian activity was least affected by the various factors. Uterine involution tended to be delayed in cows with dystocia, poor condition at calving, high milk yield and increased parity. Evaluation by multifactorial analysis of variance showed that among all the various factors examined, milk yield had the most significant effect on postpartum adrenocortical and pituitary function. High milk yield in cows apparently lead to enhanced adrenocortical function at 8 and 22 days postpartum and depressed pituitary function at 7 and 21 days postpartum