Abstract：
This study aimed to determine the effect of 2 simple breeding strategies combining artificial insemination (AI) after detection of estrus (AIED) and timed AI (TAI) on first-service fertility in lactating Holstein cows. Weekly, lactating Holstein cows (n = l,049) between 40 and 46 d in milk (DIM) were randomly assigned to initiate 1 of 2 breeding strategies for first service: Presynch-14 and PG+G. Presynch-14 is a presynchronization strategy with 2 PGF2α treatments 14 d apart with the last PGF2α 14 d before the initiation of the Ovsynch protocol. Cows treated with PG+G receive a simpler presynchronization program that uses PGF2α and GnRH simultaneously 7 d before Ovsynch. In both treatments, cows detected in standing estrus by tail chalk at any time ≥55 DIM were inseminated, and treatment was discontinued (n = 525). Cows completing treatment received TAI from 78 to 84 DIM (n = 526). In a subgroup of cows that received TAI, blood was collected (n = 163) to assess circulating concentrations of progesterone, and ultrasonographic evaluations of ovaries were performed on the day of first GnRH of Ovsynch (n = 162) and PGF2α of Ovsynch (n = 122). The proportion of cows that received TAI was greater for PG+G compared with Presynch-14 (63.5 vs. 31.9%), which increased DIM at first service for cows treated with PG+G compared with Presynch-14 (75.5 ± 0.4 vs. 68.7 ± 0.4). For cows receiving TAI, the ovulatory response to first GnRH of Ovsynch (73.8 vs. 48.8%) and the proportion of cows with functional corpora lutea (92.6 vs. 73.1%) were greater for PG+G than Presynch-14. Cows treated with PG+G had greater overall pregnancy per AI (P/AI) 42 ± 7 d after AI (40.2 vs. 33.6%) and calving per AI (32.1 vs. 25.2%) than Presynch-14. For cows receiving AIED, treatment did not affect P/AI 42 ± 7 d after AI. However, for cows receiving TAI, PG+G increased P/AI compared with Presynch-14 (44.6 vs. 35.2%). Overall, cows receiving TAI had greater P/AI 42 ± 7 d after AI (42.5 vs. 31.5%) and calving per AI (34.1 vs. 23.7%) and decreased pregnancy loss (16.8 vs. 25.2%) than cows receiving AIED. In summary, PG+G increased the proportion of cows receiving TAI and the DIM at first service, P/AI, and calving per AI compared with Presynch-14 when both TAI programs were combined with AIED.
摘要：
这项研究旨在确定在检测到发情（AIED）和定时AI（TAI）后，结合人工授精（AI）的两种简单育种策略对泌乳荷斯坦奶牛的首次服务繁殖力的影响。每周,泌乳荷斯坦奶牛(n=l，049）在40到46天之间的牛奶（DIM）被随机分配为首次服务的2种育种策略中的1种：Presynch-14和PGG。Presynch-14是一种预同步策略，其中2个PGF2α治疗间隔14d，最后一个PGF2α治疗在Ovsynch方案开始前14d。用PGG处理的母牛会收到一个更简单的预同步程序，该程序在Ovsynch之前7d同时使用PGF2α和GnRH。在这两种治疗中，在≥55DIM的任何时间通过尾巴粉笔在站立发情中检测到的母牛进行授精，并停止治疗（n=525）。完成治疗的奶牛接受从78到84DIM的TAI(n=526)。在接受TAI的奶牛亚组中，收集血液（n=163）以评估孕酮的循环浓度，在Ovsynch的GnRH（n=162）和Ovsynch的PGF2α（n=122）的第一天进行卵巢的超声检查。与Presynch-14相比，PG+G接受TAI的奶牛比例更高(63.5vs.31.9%），与Presynch-14相比，用PG+G处理的奶牛在首次服务时的DIM增加（75.5±0.4与68.7±0.4)。对于接受TAI的奶牛，Ovsynch对第一次GnRH的排卵反应（73.8vs.48.8%)和具有功能性黄体的奶牛比例(92.6vs.PG+G的73.1%)高于Presynch-14。用PG+G治疗的奶牛每AI（P/AI）42±7d在AI后（40.2vs.33.6%）和每AI产卵（32.1与25.2%）比Presynch-14。对于接受AIED的奶牛，AI后42±7d治疗不影响P/AI。然而,对于接受TAI的奶牛，与Presynch-14相比，PG+G增加了P/AI（44.6与35.2%）。总的来说,接受TAI的奶牛在AI后有更大的P/AI42±7d(42.5vs.31.5%）和每AI产卵（34.1与23.7%）和减少妊娠损失（16.8vs.25.2％）比接受AIED的奶牛高。总之,PG+G增加了首次服务时接受TAI和DIM的奶牛的比例，P/AI,当两个TAI程序与AIED结合使用时，与Presynch-14相比，每个AI产卵。
