泌乳奶牛被归类为自发排卵者,其中怀孕的建立取决于行为发情检测的准确性,以正确进行人工授精(AI)。Ovsynch协议的开发,使卵巢功能同步的荷尔蒙方案,从而允许定时AI(TAI),而无需检测发情,提供了一个管理工具,用于提高人工智能服务率,但不提高每个人工智能的怀孕率(P/AI)。对7个随机分组的回顾,对照实验将检测到发情后授精的母牛的P/AI与提交Presynch-Ovsynch或Double-Ovsynch协议后接受TAI的母牛的P/AI进行比较,支持TAI的最新程序比检测到发情后授精的母牛产生更多的P/AI。解释生育计划如何增加P/AI的生理和内分泌机制是20多年旨在提高泌乳奶牛繁殖性能的研究的结果。通过比较开放日的表型趋势与女儿怀孕率的遗传趋势和奶牛受胎率的表型趋势,我们说明了美国奶牛繁殖性能随时间的巨大变化。从1955年到2000年,开放天数增加,从2000年到2010年,开放天数急剧下降,而女儿怀孕率的遗传趋势却没有同时增加。相比之下,在过去的20年中,开放天数的急剧减少与奶牛受胎率的表型趋势的急剧增加有关。尽管许多管理因素会影响P/AI,在过去的20年中,采用和实施直接增加P/AI的TAI计划是美国泌乳奶牛繁殖性能急剧增加的重要组成部分。
Lactating dairy cows are classified as spontaneous ovulators, in which establishment of pregnancy depends on the accuracy of detection of behavioral estrus for correct timing of artificial insemination (AI). Development of the Ovsynch protocol, a hormonal protocol that synchronizes ovarian function, thereby allowing for timed AI (TAI) without the need to detect estrus, provided a management tool for increasing AI service rates but not pregnancies per AI (P/AI). A
review of 7 randomized, controlled experiments that compared P/AI of cows inseminated after a detected estrus to that of cows receiving TAI after submission to Presynch-Ovsynch or Double-Ovsynch protocols supports that the newest programs for TAI yield more P/AI than cows inseminated after a detected estrus. The physiologic and endocrine mechanisms that explain how fertility programs increase P/AI are a culmination of over 20 yr of research aimed at increasing reproductive performance in lactating dairy cows. We illustrate the dramatic change in reproductive performance of US dairy cows over time by comparing the phenotypic trend in days open with the genetic trend in daughter pregnancy rate and the phenotypic trend in cow conception rate. Whereas days open increased from 1955 to 2000, days open from 2000 to 2010 dramatically decreased without a concurrent increase in the genetic trend for daughter pregnancy rate. By contrast, the dramatic decrease in days open over the past 20 yr is associated with a dramatic increase in the phenotypic trend in cow conception rate. Although many management factors affect P/AI, adoption and implementation of TAI programs that directly increase P/AI is an important component of the dramatic increase in reproductive performance in lactating dairy cows in the United States over the past 20 yr.