Effect of human chorionic gonadotropin, on luteal function and reproductive performance of high-producing lactating Holstein dairy cows

The objectives were to evaluate effects of human chorionic gonadotropin (hC G) (3,300 IU i.m.) administered on d 5 after AI on CL number, plasma proges terone concentration, conception rate, and pregnancy loss in high-producing dairy cows. Following the synchronization of estrus and AI, 406 cows were injected with either hCG or saline on d 5 after AI in a randomized complete block design. Blood sampling and ovarian ultrasonography were conducted on ce between d 11 and 16 after AL Pregnancy diagnoses were performed on d 28 by ultrasonography and on d 45 and 90 after AI by rectal palpation. Treatme nt with hCG on d 5 resulted in 86.2% of the cows with more than one CL comp ared with 23.2% in controls. Plasma progesterone concentrations were increa sed by 5.0 ng/mL in hCG-treated cows. The presence of more than one CL incr eased progesterone concentration in hCG-treated cows but not in controls. C onception rates were higher for hCG-treated cows on d 28 (45.8 > 38.7%), 45 (40.4 > 36.3%), and 90 (38.4 > 31.9%) after AL Treatment with hCG improved conception rate in cows losing body condition between AI and d 28 after AL Pregnancy losses were similar between treatment groups. Treatment with hCG on d 5 after Al induces accessory CL, enhances plasma progesterone concent ration, and improves conception rate of high-producing dairy cows.