Influence of Experimentally-induced Clinical Mastitis on Reproductive Function of Dairy Cows

The objectives of the current studies were to determine if experimentally-induced clinical mastitis has an impact on reproductive function of lactating dairy cows. Preliminary data have indicated that clinical and subclinical mastitis are associated with increased number of days to first service, increased services per conception, and increased days open. Others have speculated that clinical mastitis may result in early luteal regression. To date, no direct effects of clinical mastitis have been documented. The initial study was to determine if alterations occurred in endocrine status of cows or alterations in stress hormone profiles. Hormones of particular interest were luteinizing hormone, prostaglandin F_2α, and cortisol. These data indicated that clinical mastitis did alter physiology of the cow by increasing concentrations of cortisol and increasing prostaglandin metabolite following oxytocin challenge. The second study was aimed to determine if clinical mastitis during the immediate preovulatory period or postovulatory period altered reproductive function. Data collected from these experiments allowed the conclusions to be made that mastitis during the immediate preovulatory period altered expression of estrus. Meanwhile, clinical mastitis during the early postovulatory period was of little consequence to normal reproductive function and pregnancy. The final study was to determine if clinical mastitis, which resulted in alterations in estrous expression during the preovulatory period altered endocrine and follicular function. Data from the experiment indicated that alterations did occur in the hypothalamo-pituitary-ovarian axis such that normal endocrine function is diminished. Collectively, data collected in these studies indicated that clinical mastitis resulted in alterations in normal endocrine function, especially during the preovulatory time period. These changes in endocrine and follicular function resulted in decreased expression of estrus, decreased ovulation, and increased days to service opportunity.