Division of Animal Sciences, University of Missouri, Columbia 65211.
J Dairy Sci. 2019 Apr;102(4):3706-3721. doi: 10.3168/jds.2018-15544. Epub 2019 Jan 26.
The establishment of pregnancy following insemination is the primary definition of fertility in most dairy systems. Highly fertile cows establish pregnancy sooner after calving and require fewer inseminations than lower-fertility cows. Pregnancy occurs through a series of individual events in sequence. In postpartum cows, for example, the uterus involutes, estrous cycles are re-established, estrus is expressed and detected, sperm are deposited in the reproductive tract and capacitate, ovulation occurs and is followed by fertilization, and the corpus luteum forms and produces sufficient progesterone to maintain pregnancy. The oviduct supports early cleavage and the uterus establishes a receptive environment for the developing pregnancy. Each individual event is theoretically heritable and these events collectively contribute to the phenotype of pregnancy after insemination. Across most dairy systems, genetic selection for fertility in cows is primarily based on reduced days from calving to pregnancy (i.e., days open). Dairy systems differ with respect to reproductive management applied to cows, which may affect the relative importance of individual components to the overall fertility of the cow. In some systems, cows are inseminated after detected estrus with minimal intervention. In these systems, days open effectively captures the summation of the individual components of fertility. More intensive systems use hormonal treatments (e.g., PGF, GnRH) followed by timed artificial insemination (AI). Timed AI does not invalidate days open but the individual components that contribute to days open may be more or less important. Selection of cows for days open within populations that are managed differently may place different pressures on the individual components of fertility. Ensuring uniform performance of future cows across a variety of reproductive management systems may require a greater understanding of the underlying genetics of the individual components of fertility.
配种后妊娠的建立是大多数奶牛养殖系统中生育力的主要定义。高生育力的奶牛在产后更早地建立妊娠，并且需要的配种次数比低生育力的奶牛少。妊娠是通过一系列连续的个体事件发生的。例如，在产后奶牛中，子宫收缩，发情周期重新建立，发情表现出来并被检测到，精子被沉积在生殖道中并获能，排卵发生，随后受精，黄体形成并产生足够的孕酮维持妊娠。输卵管支持早期分裂，子宫为发育中的妊娠建立接受环境。每个个体事件在理论上都是可遗传的，这些事件共同构成了配种后妊娠的表型。在大多数奶牛养殖系统中，对奶牛生育力的遗传选择主要基于从分娩到妊娠的天数减少（即发情天数）。奶牛的生殖管理在不同的奶牛养殖系统中有所不同，这可能会影响个别组成部分对奶牛整体生育力的相对重要性。在一些系统中，奶牛在检测到发情后进行人工授精，干预最小。在这些系统中，发情天数有效地捕捉到了生育力各个组成部分的总和。更密集的系统使用激素处理（例如 PGF、GnRH），然后进行定时人工授精（AI）。定时 AI 不会使发情天数失效，但有助于发情天数的个别组成部分可能更为重要或不太重要。在不同管理方式的牛群中，选择发情天数可能会对生育力的各个组成部分施加不同的压力。要确保未来的奶牛在各种生殖管理系统中表现一致，可能需要更深入地了解生育力各个组成部分的潜在遗传学。
