Department of Animal Science, McGill University, Sainte-Anne-de-Bellevue, Quebec H9X 3V9, Canada.
Department of Animal Science, McGill University, Sainte-Anne-de-Bellevue, Quebec H9X 3V9, Canada.
J Dairy Sci. 2022 Feb;105(2):1255-1264. doi: 10.3168/jds.2021-20214. Epub 2021 Nov 17.
Studies of dairy cow longevity usually focus on the animal life after first calving, with few studies considering early life conditions and their effects on longevity. The objective was to evaluate the effect of birth conditions routinely collected by Dairy Herd Improvement agencies on offspring longevity measured as length of life and length of productive life. Lactanet provided 712,890 records on offspring born in 5,425 Quebec dairy herds between January 1999 and November 2015 for length of life, and 506,066 records on offspring born in 5,089 Quebec dairy herds between January 1999 and December 2013 for length of productive life. Offspring birth conditions used in this study were calving ease (unassisted, pull, surgery, or malpresentation), calf size (small, medium, or large), and twinning (yes or no). Observations were considered censored if the culling reason was "exported," "sold for dairy production," or "rented out" as well as if the animals were not yet culled at the time of data extraction. If offspring were not yet culled when the data were extracted, the last test-day date was considered the censoring date. Conditional inference survival trees were used in this study to analyze the effect of offspring birth conditions on offspring longevity. The hazard ratio of culling between the groups of offspring identified by the survival trees was estimated using a Cox proportional hazard model with herd-year-season as a frailty term. Five offspring groups were identified with different length of life based on their birth condition. Offspring with the highest length of life [median = 3.61 year; median absolute deviation (MAD) = 1.86] were those classified as large or medium birth size and were also the result of an unassisted calving. Small offspring as a result of a twin birth had the lowest length of life (median = 2.20 year; MAD = 1.69) and were 1.52 times more likely to be culled early in life. Six groups were identified with different length of productive life. Offspring that resulted from an unassisted or surgery calving and classified as large or medium when they were born were in the group with the highest length of productive life (median = 2.03 year; MAD = 1.63). Offspring resulting from a malpresentation or pull in a twin birth were in the group with the lowest length of productive life (median = 1.15 year; MAD = 1.11) and were 1.70 times more likely to be culled early in life. In conclusion, birth conditions of calving ease, calf size, and twinning greatly affected offspring longevity, and such information could be used for early selection of replacement candidates.
奶牛长寿的研究通常集中在首次产犊后的动物生命上，很少有研究考虑早期生活条件及其对长寿的影响。本研究旨在评估奶牛群改良机构常规收集的出生条件对后代寿命（即生命长度和生产寿命）的影响。Lactanet 提供了 1999 年 1 月至 2015 年 11 月期间在魁北克的 5425 个奶牛场出生的 712890 头后代的寿命记录，以及 1999 年 1 月至 2013 年 12 月期间在魁北克的 5089 个奶牛场出生的 506066 头后代的生产寿命记录。本研究中使用的后代出生条件包括产犊难易程度（自然分娩、牵引、手术或胎位不正）、犊牛大小（小、中、大）和双胞胎（是或否）。如果淘汰原因是“出口”、“出售用于奶牛生产”或“出租”，或者在数据提取时动物尚未淘汰，则认为观察结果被删失。如果数据提取时后代尚未淘汰，则最后一次测试日期被视为删失日期。本研究使用条件推理生存树来分析后代出生条件对后代长寿的影响。使用带有畜群-年份-季节作为脆弱性项的 Cox 比例风险模型来估计生存树确定的后代组之间的淘汰风险比。根据出生条件，确定了 5 个具有不同寿命的后代组。寿命最长的后代（中位数=3.61 年；中位数绝对偏差（MAD）=1.86）是那些被归类为大或中出生大小的后代，并且是自然分娩的结果。双胞胎出生的小犊牛寿命最短（中位数=2.20 年；MAD=1.69），早期淘汰的可能性高 1.52 倍。根据生产寿命，确定了 6 个具有不同生产寿命的组。自然分娩或手术分娩的后代，如果出生时被归类为大或中，那么他们处于生产寿命最长的组（中位数=2.03 年；MAD=1.63）。由于胎位不正或牵引而在双胞胎中出生的后代处于生产寿命最短的组（中位数=1.15 年；MAD=1.11），并且早期淘汰的可能性高 1.70 倍。总之，产犊难易程度、犊牛大小和双胞胎的出生条件极大地影响了后代的寿命，这些信息可用于早期选择后备牛。
