Kadokawa Hiroya, Martin Graeme B
Department of Animal Breeding and Reproduction, National Institute of Livestock and Grassland Science, Nasushiobara, Tochigi, Japan.
J Reprod Dev. 2006 Feb;52(1):161-8. doi: 10.1262/jrd.17088.
For lactating dairy cows, we need management tools, that are "clean, green and ethical", cost-effective and easy to use. Specific tools are needed for artificial insemination (AI) after oestrus detection within a few months of calving, and for managing the complex nutritional requirements of cows between successive calvings. Assessment of energy deficit by measurement of body condition score (BCS) has been useful in the past but we now need more sophisticated ways to measure the relationship between adipose tissue and fertility. For this reason, we have focused our attention on the cells of the adipose tissue, the adipocytes, and the role of the hormone that they produce, leptin. This hormone affects pulsatile LH release and, in dairy cows, it seems to be linked to the first postpartum ovulation. Adipocytes are always sensing energy status and they control leptin secretion dynamically, so blood leptin concentrations can change acutely, even when there is no detectable change in BCS. Leptin secretion seems to be determined by the secretory activity of each adipocyte as well as the total mass of adipocytes in the body of the animal (as measured by BCS). The strong relationship between BCS, leptin concentration and reproductive function in dairy cows suggests that we should reconsider the interval of the recovery from prepartum and postpartum damages, the need for high milk yields at the last lactation causing the dry-off stress and the subsequent troubles. We should also re-assess the current drive to reduce calving interval because milk yields during the early stages of lactation are economically very important but high yields seem to cause several metabolic and reproductive disorders in modern dairy cows. In general, the thinking has been that calving interval must be short because short intervals are more profitable. However, if we remember that main product from dairy cows is milk and that a short calving interval is very difficult without reproductive problems, then a longer calving interval might be more sensible and also more profitable. We have example of an extended calving interval in Japan, Supercows which are very rare cows yielding remarkable high milk. Finally, we probably need to improve dairy cows genetically if we are to achieve the goal of "clean, green and ethical" dairy farming. This paper reviews data relevant to these strategies and we conclude that more basic and applied research will be required if we are to find ways to reach that goal.
对于泌乳奶牛，我们需要“清洁、绿色且符合道德规范”、具有成本效益且易于使用的管理工具。在产犊后几个月内进行发情检测后进行人工授精（AI），以及管理奶牛在连续产犊之间复杂的营养需求，都需要特定的工具。过去，通过测量体况评分（BCS）来评估能量亏空很有用，但现在我们需要更复杂的方法来测量脂肪组织与繁殖力之间的关系。因此，我们将注意力集中在脂肪组织的细胞——脂肪细胞，以及它们产生的激素——瘦素的作用上。这种激素会影响促黄体生成素（LH）的脉冲式释放，在奶牛中，它似乎与产后首次排卵有关。脂肪细胞一直在感知能量状态，并动态控制瘦素的分泌，所以即使BCS没有可检测到的变化，血液中的瘦素浓度也可能会急剧变化。瘦素的分泌似乎取决于每个脂肪细胞的分泌活动以及动物体内脂肪细胞的总质量（通过BCS测量）。奶牛的BCS、瘦素浓度与繁殖功能之间的密切关系表明，我们应该重新考虑从产前和产后损伤中恢复的间隔时间，以及上一胎高产奶量导致干奶应激和后续问题的必要性。我们还应该重新评估当前缩短产犊间隔的驱动力，因为泌乳早期的产奶量在经济上非常重要，但高产似乎会在现代奶牛中引发多种代谢和繁殖紊乱。一般来说，人们一直认为产犊间隔必须短，因为短间隔更有利可图。然而，如果我们记住奶牛的主要产品是牛奶，而且没有繁殖问题很难实现短产犊间隔，那么较长产犊间隔可能更明智，也更有利可图。我们有日本延长产犊间隔的例子，超级奶牛是非常罕见的产奶量极高的奶牛。最后，如果我们要实现“清洁、绿色且符合道德规范”的奶牛养殖目标，可能需要对奶牛进行基因改良。本文回顾了与这些策略相关的数据，我们得出结论，如果我们要找到实现该目标的方法，将需要更多的基础研究和应用研究。
