LeBlanc Stephen
Population Medicine, Ontario Veterinary College, University of Guelph, Canada NC1G 2W1, Canada.
J Reprod Dev. 2010 Jan;56 Suppl:S1-7. doi: 10.1262/jrd.1056s01.
There is much debate about possible antagonism between high milk production and reproductive performance. This paper reviews methods of measuring reproductive performance and the association of the level of milk production with pregnancy rate at the herd and individual levels. The main question is whether fertility (the capacity for reproductive function and successful pregnancy) of dairy cows has in fact declined, as opposed to the success of management systems and people at meeting the metabolic, nutritional, housing, and social needs of increasingly productive animals but with no less inherent capacity to achieve and maintain pregnancy; and if fertility really has diminished, the extent to which this decline is caused by increased milk production. There is no doubt that production per cow has increased, but it is unclear how much of this increase can explain the apparent decrease in fertility. It is important to separate the biology of reproductive function from the effects of economically based management decisions about culling and continuation of breeding. Most traditionally-used measures of reproductive performance (calving interval, conception rate, non-return rate) are incomplete or severely biased outcome measures. Both herd and cow-level data should include as much information as possible on confounders of the relationship of production with reproduction. Population or herd-level data should not be used to make inferences about individual-level associations. Considering the quality of data and analytic methods in the published literature, it is not clear if there is any association between higher milk yield and the probability and timing of pregnancy, either among cows at various levels of production in a population at one time, or with increasing production over time.
关于高产奶量与繁殖性能之间可能存在的拮抗关系存在诸多争议。本文综述了测量繁殖性能的方法以及群体和个体水平上产奶量与妊娠率之间的关联。主要问题是，奶牛的繁殖力（生殖功能和成功受孕的能力）是否实际上已经下降，这与管理系统和人员满足日益高产动物的代谢、营养、住房和社会需求的成功情况形成对比，但动物实现和维持妊娠的内在能力并未降低；如果繁殖力确实下降了，那么这种下降在多大程度上是由产奶量增加所致。毫无疑问，每头奶牛的产量都有所提高，但尚不清楚这种提高中有多少可以解释繁殖力明显下降的原因。将生殖功能的生物学特性与基于经济的淘汰和继续繁殖管理决策的影响区分开来很重要。大多数传统使用的繁殖性能衡量指标（产犊间隔、受孕率、不返情率）都是不完整或存在严重偏差的结果指标。群体和个体水平的数据都应尽可能多地包含有关产奶量与繁殖关系的混杂因素的信息。不应使用群体或畜群水平的数据来推断个体水平的关联。考虑到已发表文献中的数据质量和分析方法，目前尚不清楚在同一时间不同生产水平的奶牛群体中，或者随着时间推移产奶量增加的情况下，较高的产奶量与妊娠的概率和时间之间是否存在任何关联。
