Pregnancy maintenance in heat stressed dairy cows with gonadotropin-releasing hormone and human chorionic gonadotropin

Abstract

Heat stress is one of the main factors associated with low reproductive performance in dairy cows and causes economic losses in high-producing dairy herds throughout the world, especially in tropical areas. Although the exact mechanisms by which heat stress affects fertility is unknown, some theories propose that excessive heat has detrimental effects on follicular development and on progesterone production during the luteal phase of the estrous cycle, which subsequently results in increased rates of early embryonic death (EED). Thus, increasing progesterone concentration could increase fertility in heat stressed dairy herds. One way to achieve an increased progesterone concentration is to support the corpus luteum (CL), the source of progesterone secretion, by means of gonadotropin-releasing hormone (GnRH) or human chorionic gonadotropin (hCG). The objective of this study was to determine whether injection of either two doses of GnRH or a single dose of hCG would increase pregnancy survival in high-producing, heat-stressed dairy cows.