McDougall Scott
Animal Health Centre, Morrinsville, New Zealand.
J Reprod Dev. 2006 Feb;52(1):185-94. doi: 10.1262/jrd.17091.
Internationally, reproductive performance of dairy cattle is declining. Under the low production, pasture-based and seasonal calving system used in New Zealand, reproductive performance is also declining, but remains higher than for many other industries. The seasonal calving system requires a high level of reproductive performance to ensure a 365 day inter-calving interval. About 80% of cows are detected in oestrus and inseminated in the first 3 weeks of the seasonal breeding programme and have a conception rate of 55% to 65% to this first insemination. This results in approximately 75% and approximately 90% of cows being pregnant by 6 weeks and by the end of the breeding programme, respectively. However, reproductive performance is declining due to multiple factors including increasing herd size, reduced oestrus detection sensitivity and specificity, declining body condition score at calving and increased rate of body condition score loss postpartum. Continuing selection for increased milk production is also having negative effects on reproduction. The mechanisms by which high production and negative energy balance are reducing reproductive performance are becoming better understood. However, practical solutions for the problem are challenging for veterinarians and consultants, especially given the consumer preference for less interventions.
在国际上，奶牛的繁殖性能正在下降。在新西兰采用的低产量、以牧场为基础的季节性产犊系统下，繁殖性能也在下降，但仍高于许多其他行业。季节性产犊系统需要高水平的繁殖性能来确保365天的产犊间隔。在季节性繁殖计划的前3周，约80%的母牛被检测出发情并进行授精，首次授精的受孕率为55%至65%。这导致约75%的母牛在6周时怀孕，约90%的母牛在繁殖计划结束时怀孕。然而，由于多种因素，包括牛群规模扩大、发情检测敏感性和特异性降低、产犊时体况评分下降以及产后体况评分损失率增加，繁殖性能正在下降。持续选择提高产奶量也对繁殖产生负面影响。高产和负能量平衡降低繁殖性能的机制正逐渐被更好地理解。然而，对于兽医和顾问来说，解决这个问题的实际方案具有挑战性，特别是考虑到消费者对较少干预的偏好。
