Harman J L, Gröhn Y T, Erb H N, Casella G
Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
Am J Vet Res. 1996 May;57(5):634-9.
To quantify the effect of early-lactation milk and milk fat production on time to conception.
Event-time analysis (survival analysis).
44,450 cows delivering calves between September 1985 and September 1986, from 6,227 Ayrshire dairy herds in 80 Finnish communities.
Primiparous and multiparous cows were analyzed in separate Cox proportional hazards models. 60-day milk and milk fat production were categorized and regressed against days from parturition to conception for the period 56 to 120 postpartum days, controlling for season of parturition, parity, herd production, occurrence of 43 diseases, and community.
Multiparous cows producing above the 80th percentile for 60-day milk, but with milk fat production below the 75th percentile, were significantly more likely to conceive, compared with cows with lower production and compared with cows with similar milk production but with milk fat between the 75th and 97th percentiles. They were slightly more likely to conceive than cows with highest milk fat production, although not significantly so. Primiparous cows producing above the 80th percentile for 60-day milk with milk fat below the 75th percentile also had the highest conception probability. The highest producing primiparae had significantly lower conception probability than all others.
Controlling for disease occurrence, calving season, parity, herd production level, and community, there appeared to be an inverted U-shaped relation between 60-day production and conception probability.
Primiparous cows that are high producers may not be receiving the same careful management that high-producing multiparous cows receive.
量化早期泌乳期牛奶和乳脂产量对受孕时间的影响。
事件时间分析（生存分析）。
1985年9月至1986年9月间产犊的44450头奶牛，来自芬兰80个社区的6227个艾尔夏奶牛群。
在单独的Cox比例风险模型中对初产和经产奶牛进行分析。将产后56至120天内60天的牛奶和乳脂产量进行分类，并针对从分娩到受孕的天数进行回归分析，同时控制分娩季节、胎次、牛群产量、43种疾病的发生情况以及社区因素。
60天牛奶产量高于第80百分位数但乳脂产量低于第75百分位数的经产奶牛，与产量较低的奶牛以及牛奶产量相似但乳脂产量在第75至97百分位数之间的奶牛相比，受孕的可能性显著更高。与乳脂产量最高的奶牛相比，它们受孕的可能性略高，但差异不显著。60天牛奶产量高于第80百分位数且乳脂产量低于第75百分位数的初产奶牛受孕概率也最高。产量最高的初产奶牛受孕概率显著低于其他所有奶牛。
在控制疾病发生、产犊季节、胎次、牛群产量水平和社区因素后，60天产量与受孕概率之间似乎呈倒U形关系。
高产初产奶牛可能没有得到与高产经产奶牛相同的精心管理。
