Melo L F, Monteiro P L J, Surjus R S, Drum J N, Wiltbank M C, Sartori R
Department of Animal Science, University of São Paulo, Piracicaba, SP 13418-900 Brazil.
Department of Dairy Science, University of Wisconsin-Madison, Madison 53706.
J Dairy Sci. 2016 Nov;99(11):9227-9237. doi: 10.3168/jds.2016-11220. Epub 2016 Aug 24.
Our objectives were to evaluate ovarian dynamics and fertility comparing 2 treatments at the start of a progesterone (P4)-based fixed-time artificial insemination (FTAI) protocol and 2 treatments at the end of the protocol. Thus, 1,035 lactating Holstein cows were assigned in a random phase of the estrous cycle to 1 of 4 treatments using a completely randomized design with a 2×2 factorial arrangement. At the beginning of the protocol (d -10), cows received GnRH or estradiol benzoate (EB) and, at the end, EB (d -1) or estradiol cypionate (ECP; d -2), resulting in 4 treatments: GnRH-EB, GnRH-ECP, EB-EB, and EB-ECP. All cows received an intravaginal P4 device on d -10, which was removed on d -2. Cows also received PGF on d -3 and -2. The FTAI was performed on d 0. Ovaries were evaluated by ultrasound for corpus luteum (CL) presence and regression (d -10 and -3) and follicle measurements (d -10 and 0), as well as the uterus for percentage pregnant per AI (P/AI; d 32 and 60). Blood samples were collected (d -10 and -3) for P4 measurements. Treatment with GnRH rather than EB tended to increase P/AI on d 32 (38.2 vs. 33.7%) and on d 60 (32.9 vs. 28.9%). More cows treated with GnRH had CL on d -3 compared with EB-treated cows (77.3 vs. 58.3%), due to less CL regression between d -10 and -3 (24.7 vs. 43.8%) and more cows with a new CL on d -3 (35.9 vs. 25.0%). Cows treated with GnRH also had greater P4 concentrations on d -3 than EB cows (3.4 vs. 2.0 ng/mL). Increased circulating P4 at the start of the protocol (d -10) decreased the probability of ovulation to EB or GnRH at that time. Cows from GnRH group also ovulated a larger-diameter follicle at the end of the protocol (15.5 vs. 14.7mm). No difference between EB and ECP in P/AI on d 32 (34.8 vs. 37.0) and 60 (30.8 vs. 31.0%) or in pregnancy loss (11.1 vs. 15.4%) was detected and we found no interaction between treatments for P/AI. Independent of treatment, cows with CL on d -10 and -3 had the greatest P/AI on d 60 (36.9%). In conclusion, treatments at the end of the protocol were similar for ECP or EB and we found no additive effect or interactions on P/AI between treatments. However, cows treated with GnRH rather than EB on d -10 had less luteolysis and tended to have greater P/AI, probably because P4 concentrations were greater during the protocol. Finally, regardless of treatments, cows with CL at the beginning of the protocol as well as at the time of PGF had greater fertility.
我们的目标是在基于孕酮（P4）的定时人工授精（FTAI）方案开始时比较两种处理方式，并在方案结束时比较另外两种处理方式，以此评估卵巢动态和繁殖力。因此，1035头泌乳期荷斯坦奶牛在发情周期的随机阶段，采用完全随机设计和2×2析因安排，被分配到4种处理方式中的一种。在方案开始时（第-10天），奶牛接受促性腺激素释放激素（GnRH）或苯甲酸雌二醇（EB），在结束时，接受EB（第-1天）或环丙孕酮（ECP；第-2天），从而形成4种处理方式：GnRH-EB、GnRH-ECP、EB-EB和EB-ECP。所有奶牛在第-10天放置阴道内P4装置，并在第-2天取出。奶牛在第-3天和第-2天还接受了前列腺素F2α（PGF）。定时人工授精在第0天进行。通过超声评估卵巢黄体（CL）的存在和消退情况（第-10天和第-3天）以及卵泡大小（第-10天和第0天），同时评估子宫的每次人工授精妊娠率（P/AI；第32天和第60天）。在第-10天和第-3天采集血样进行P4测定。与EB处理的奶牛相比，GnRH处理的奶牛在第32天（38.2%对33.7%）和第60天（32.9%对28.9%）的P/AI有增加趋势。与EB处理的奶牛相比，GnRH处理的奶牛在第-3天有更多的CL（77.3%对58.3%），这是因为在第-10天至第-3天期间CL消退较少（24.7%对43.8%），且在第-3天有更多新的CL（35.9%对25.0%）。GnRH处理的奶牛在第-3天的P4浓度也高于EB处理的奶牛（3.4对2.0 ng/mL）。在方案开始时（第-10天）循环P4的增加降低了此时对EB或GnRH排卵的概率。GnRH组的奶牛在方案结束时排卵的卵泡直径也更大（15.5对14.7mm）。未检测到EB和ECP在第32天（34.8%对37.0%）和第60天（30.8%对31.0%）的P/AI或妊娠损失（11.1%对15.4%）之间存在差异，并且我们发现处理方式之间在P/AI方面没有交互作用。与处理方式无关，在第-10天和第-3天有CL的奶牛在第60天的P/AI最高（36.9%）。总之，方案结束时ECP或EB的处理方式相似，并且我们发现处理方式之间在P/AI方面没有累加效应或交互作用。然而，在第-10天用GnRH而非EB处理的奶牛黄体溶解较少，并且P/AI有增加趋势，这可能是因为在方案期间P4浓度更高。最后，无论处理方式如何，在方案开始时以及PGF时具有CL的奶牛繁殖力更高。
