Santos J E P, Bisinotto R S, Ribeiro E S, Lima F S, Greco L F, Staples C R, Thatcher W W
Department of Animal Sciences, University of Florida, Gainesville FL 32611, USA.
Soc Reprod Fertil Suppl. 2010;67:387-403. doi: 10.7313/upo9781907284991.030.
The establishment and maintenance of pregnancy in lactating dairy cows is a complex biological event that is influenced by a multitude of factors, from the reproductive biology of the cow to managerial aspects of the dairy farm. It is often mentioned in the scientific literature that fertility in dairy cows has declined concurrent with major advances in milk production. Some of this decline is attributed to the negative genetic correlation between milk production and reproduction. In the United States, yearly production per cow has increased steadily at a rate of 1.3% in the last decade and it is likely that this trend will continue in the years to come. At this rate, the average cow in the United States will be producing over 14 tons of milk per year in 2050 and technologies will have to be developed to allow these cows to reproduce to maintain the sustainability of dairy production. Despite high production, it is not uncommon for dairy herds with rolling herd averages for milk yield above 11,000 kg to overcome the challenges of reproduction and obtain satisfactory reproductive performance. Among other things, those herds have been able to mitigate some of the mechanisms that suppress reproduction in dairy cows such as extended postpartum anovulatory period, poor estrous detection, low pregnancy per insemination and, to a lesser extent, the high pregnancy loss. The success of those farms comes from an integrated approach to fertility that includes adequate cow comfort, elaborated transition cow management and nutrition, aggressive postpartum health monitoring program with preventative and curative measures to mitigate the negative effects of diseases on reproduction, and a sound reproductive program that includes manipulation of the ovarian cycle to allow for increased insemination rate. More recently, introduction of fertility traits in selection programs have created new opportunities for improved reproduction without neglecting economically important production traits.
泌乳奶牛妊娠的建立和维持是一个复杂的生物学过程，受到多种因素的影响，从奶牛的生殖生物学特性到奶牛场的管理方面。科学文献中经常提到，奶牛的繁殖力随着牛奶产量的大幅提高而下降。这种下降部分归因于产奶量与繁殖力之间的负遗传相关性。在美国，过去十年每头奶牛的年产量以1.3%的速度稳步增长，未来几年这种趋势可能会持续。按照这个速度，到2050年美国平均每头奶牛每年将产奶超过14吨，因此必须开发相关技术，使这些奶牛能够繁殖，以维持奶牛生产的可持续性。尽管产量很高，但对于牛群平均产奶量超过11000千克的奶牛场来说，克服繁殖方面的挑战并获得令人满意的繁殖性能并不罕见。其中，这些牛群能够缓解一些抑制奶牛繁殖的机制，如产后排卵延迟、发情检测不佳、每次输精后的低妊娠率以及在较小程度上的高妊娠损失率。这些农场的成功源于一种综合的繁殖力管理方法，包括确保奶牛足够舒适、精心管理围产期奶牛和提供营养、积极开展产后健康监测计划并采取预防和治疗措施以减轻疾病对繁殖的负面影响，以及制定完善的繁殖计划，包括调控卵巢周期以提高输精率。最近，在选种计划中引入繁殖性状为改善繁殖性能创造了新机会，同时又不忽视经济上重要的生产性状。
