Rivera H, Lopez H, Fricke P M
Department of Dairy Science, University of Wisconsin, Madison 53706, USA.
J Dairy Sci. 2004 Jul;87(7):2051-61. doi: 10.3168/jds.S0022-0302(04)70023-5.
Nonlactating Holstein dairy heifers (n=352) 13 mo of age were managed using a 42-d artificial insemination (AI) breeding period in which they received AI after removed tail chalk evaluated once daily. At AI breeding period onset (d 0), heifers were randomly assigned to receive synchronization of ovulation (100 microg of GnRH, d 0; 25 mg of PGF2alpha, d 6; 100 microg of GnRH, d 8) and timed AI (TAI; d 8) and AI after removed tail chalk for the entire AI breeding period (GPG; n=175), or AI after removed tail chalk for the entire AI breeding period (TC; n=177). As expected, 17.7% (31/175) of GPG heifers received AI after removed tail chalk before scheduled TAI. Pregnancy rate per artificial insemination (PR/AI) at approximately 30 d after first AI tended to be greater for TC (46.5%) than for GPG (38.3%) heifers. No treatment x inseminator interaction was detected; however, overall PR/AI was low for heifers in both treatments due to variation among the 3 inseminators (24.8, 30.0, and 58.0%). Pregnancy loss from approximately 30 to approximately 75 d after first AI was 10% and did not differ between treatments. Based on survival analysis, days to first AI was greater for TC than for GPG heifers, whereas days to pregnancy across the 42-d AI breeding period did not differ between treatments. Overall, 81.2% of GPG heifers receiving TAI synchronized luteal regression and ovulated within 48 h after the second GnRH injection. We conclude that this synchronization protocol can yield acceptable fertility in dairy heifers if AI to estrus is conducted between treatment with GnRH and PGF2alpha and AI efficiency is optimized.
13月龄的非泌乳荷斯坦奶牛小母牛（n = 352头）在42天的人工授精（AI）配种期内进行管理，在此期间，每天对其尾粉笔标记去除情况进行评估，去除尾粉笔标记后进行人工授精。在AI配种期开始时（第0天），小母牛被随机分配接受排卵同步处理（第0天注射100微克促性腺激素释放激素（GnRH）；第6天注射25毫克前列腺素F2α（PGF2α）；第8天注射100微克GnRH）和定时人工授精（TAI；第8天），并在整个AI配种期根据尾粉笔标记去除情况进行人工授精（GPG组；n = 175头），或在整个AI配种期仅根据尾粉笔标记去除情况进行人工授精（TC组；n = 177头）。正如预期的那样，17.7%（31/175）的GPG组小母牛在预定的TAI之前因尾粉笔标记去除而接受了人工授精。首次人工授精后约30天的每次人工授精受胎率（PR/AI），TC组（46.5%）倾向于高于GPG组（38.3%）小母牛。未检测到处理×输精员的交互作用；然而，由于3名输精员之间存在差异（24.8%、30.0%和58.0%），两种处理方式下小母牛的总体PR/AI都较低。首次人工授精后约30天至约75天的妊娠损失为10%，两种处理方式之间没有差异。基于生存分析，TC组小母牛至首次人工授精的天数比GPG组多，而在42天的AI配种期内至妊娠的天数在两种处理方式之间没有差异。总体而言，81.2%接受TAI的GPG组小母牛在第二次GnRH注射后48小时内黄体退化同步并排卵。我们得出结论，如果在GnRH和PGF2α处理之间进行发情人工授精并优化人工授精效率，这种同步方案可以在奶牛小母牛中产生可接受的繁殖力。
