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):640-5.
To quantify the effect of season of parturition, parity, and various diseases 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 for postpartum days 56 to 120. Occurrence of 43 diseases or disorders was recorded; codes were condensed into 25 variables offered to each model. Season of parturition was categorized into spring, summer, and fall-winter; for multiparous cows, 3 categorical variables represented parity. Models controlled for 60-day milk and milk fat production, herd milk production, and community. For all observations, parturition-to-conception interval was plotted against calendar day of parturition.
For multiparous cows, parturition in the spring or summer and being of parity 2 or 3-4 (vs older) increased the chance of conceiving; 10 diseases or disorders decreased this probability. Similarly, in the model for primiparae, parturition in spring or summer increased the probability of conception, and 6 disorders decreased it. Disorders that were detrimental in both models were anestrus, ovulatory dysfunction, other infertility, late metritis, and clinical ketosis.
The effect of season on the parturition-to-conception interval was marked at this latitude. Parturition during late April, causing confluence of postpartum day 55 with the summer solstice, was associated with the shortest parturition-to-conception intervals. Ketosis was found to be an important factor in lengthening the parturition-to-conception interval, highlighting the effect of negative energy balance on postpartum restoration of reproductive function.
量化分娩季节、胎次及各种疾病对受孕时间的影响。
事件时间分析（生存分析）。
1985年9月至1986年9月间，来自芬兰80个社区6227个艾尔夏奶牛场的44450头产犊母牛。
在产后第56至120天的单独Cox比例风险模型中，对初产和经产母牛进行分析。记录43种疾病或病症的发生情况；编码被归纳为25个变量纳入每个模型。分娩季节分为春季、夏季和秋冬；对于经产母牛，3个分类变量代表胎次。模型控制了60天的产奶量和乳脂产量、牛群产奶量及社区因素。对于所有观察对象，绘制分娩至受孕间隔与分娩日历日的关系图。
对于经产母牛，春季或夏季分娩以及胎次为2或3 - 4（相对于更高胎次）会增加受孕几率；10种疾病或病症会降低此概率。同样，在初产母牛模型中，春季或夏季分娩会增加受孕概率，6种病症会降低受孕概率。在两个模型中均有不利影响的病症是发情期缺失、排卵功能障碍、其他不孕症、晚期子宫炎和临床酮病。
在这个纬度，季节对分娩至受孕间隔的影响很显著。4月下旬分娩，使产后第55天与夏至重合，与最短的分娩至受孕间隔相关。发现酮病是延长分娩至受孕间隔的一个重要因素，突出了负能量平衡对产后生殖功能恢复的影响。
