Aréchiga C F, Staples C R, McDowell L R, Hansen P J
Department of Dairy and Poultry Sciences, University of Florida, Gainesville 32611-0920, USA.
J Dairy Sci. 1998 Feb;81(2):390-402. doi: 10.3168/jds.S0022-0302(98)75589-4.
In three experiments, we tested the efficacy of timed artificial insemination (AI) and beta-carotene supplementation for improvement of reproduction and milk yield. Experiments 1 and 2 were conducted during hot months, and Experiment 3 was conducted during cooler months. Cows were fed rations supplemented with beta-carotene at 0 or 400 mg/d per cow for > or = 15 d before the first AI. Cows were inseminated at each observed estrus after 70 d (Experiment 1) or at 50 d postpartum (Experiments 2 and 3) or were included in a timed AI program [d 0 (i.e., approximately 40 or 60 d postpartum), 8 micrograms of GnRH agonist; d 7, 25 mg of PGF2 alpha; d 9, 8 micrograms of GnRH agonist; d 10, AI] for first breeding. Pregnancy rate at first AI was similar among groups, but the percentage of cows that were pregnant by 90 d postpartum was greater for cows in the timed AI group in Experiments 1 (16.6% vs. 9.8%) and 2 (34.3% vs. 14.3%) but not in Experiment 3 (24.1% vs. 28.7%). Overall, beta-carotene had no effect on reproductive function. For cows fed supplemental beta-carotene for > or = 90 d, however, pregnancy rate at 120 d postpartum was increased in Experiment 1 (35.4% vs. 21.1%). In all experiments, beta-carotene increased cumulative milk yield on the last test day by 6 to 11%. In conclusion, timed AI can improve pregnancy rates during periods of heat stress. Supplemental beta-carotene may increase pregnancy rates for cows in the summer and can increase milk yield.
在三项试验中，我们测试了定时人工授精（AI）和补充β-胡萝卜素对改善繁殖性能和产奶量的效果。试验1和试验2在炎热月份进行，试验3在较凉爽的月份进行。在首次人工授精前≥15天，给奶牛饲喂添加β-胡萝卜素的日粮，添加量为每头奶牛0或400毫克/天。奶牛在70天（试验1）或产后50天（试验2和试验3）每次观察到发情时进行人工授精，或者纳入定时人工授精程序（第0天，即产后约40或60天，8微克促性腺激素释放激素激动剂；第7天，25毫克前列腺素F2α；第9天，8微克促性腺激素释放激素激动剂；第10天，人工授精）进行首次配种。首次人工授精时的妊娠率在各处理组间相似，但在试验1（16.6%对9.8%）和试验2（34.3%对14.3%）中，定时人工授精组产后90天时怀孕的奶牛百分比更高，而试验3中并非如此（24.1%对28.7%）。总体而言，β-胡萝卜素对繁殖功能没有影响，但在试验1中，对于饲喂补充β-胡萝卜素≥90天的奶牛，产后120天时的妊娠率有所提高（35.4%对21.1%）。在所有试验中，β-胡萝卜素使最后测试日的累计产奶量提高了6%至*11%。总之，定时人工授精可提高热应激期间的妊娠率。补充β-胡萝卜素可能会提高夏季奶牛的妊娠率，并能增加产奶量。
