Butler W R
Department of Animal Science, Cornell University, Ithaca, NY 14853-4801, USA.
J Dairy Sci. 1998 Sep;81(9):2533-9. doi: 10.3168/jds.S0022-0302(98)70146-8.
Milk production and dry matter intake of dairy cows are stimulated in response to increased intake of dietary protein, but, unfortunately, decreased fertility is often associated with this nutritional strategy. Ruminally degradable protein or ruminally undegradable protein in excess of requirement can contribute to reduced fertility in lactating cows. Dietary protein nutrition or utilization and the associated effects on ovarian or uterine physiology have been monitored with urea nitrogen in plasma or milk; concentrations above 19 mg/dl have been associated with altered uterine pH and reduced fertility in dairy cows. The uterine pH changed dynamically and inversely with plasma urea nitrogen, signaling possible changes in the uterine milieu. Mechanisms for reduced fertility include exacerbation of negative energy balance and reduced plasma progesterone concentrations when cows were fed rations that were high in ruminally degradable intake protein. Alternatively, changes in uterine secretions that are associated with high protein intake and elevated plasma urea nitrogen might be detrimental to embryos. Bovine endometrial cells in culture respond directly to increasing urea concentrations with alteration in pH gradient but respond most notably with increased secretion of prostaglandin F2 alpha (PGF2 alpha). Increased uterine luminal PGF2 alpha interferes with embryo development and survival in cows, thus providing a plausible link between elevated plasma urea nitrogen concentrations and decreased fertility. Poor fertility in high producing dairy cows reflects the combined effects of a uterine environment that is dependent on progesterone and rendered suboptimum by the antecedent effects of negative energy balance or postpartum health problems and that is further compromised by the effects of urea resulting from intake of high dietary protein.
奶牛的产奶量和干物质摄入量会因日粮蛋白质摄入量增加而受到刺激，但不幸的是，这种营养策略往往与繁殖力下降有关。瘤胃可降解蛋白或超过需求的瘤胃不可降解蛋白会导致泌乳奶牛繁殖力降低。日粮蛋白质营养或利用情况以及对卵巢或子宫生理的相关影响已通过血浆或牛奶中的尿素氮进行监测；血浆尿素氮浓度高于19毫克/分升与奶牛子宫pH值改变和繁殖力降低有关。子宫pH值随血浆尿素氮动态反向变化，表明子宫内环境可能发生变化。繁殖力降低的机制包括当奶牛饲喂瘤胃可降解摄入蛋白含量高的日粮时，负能量平衡加剧和血浆孕酮浓度降低。另外，与高蛋白摄入和血浆尿素氮升高相关的子宫分泌物变化可能对胚胎有害。培养的牛子宫内膜细胞会直接随着尿素浓度增加而使pH梯度改变，但最显著的反应是前列腺素F2α（PGF2α）分泌增加。子宫腔内PGF2α增加会干扰奶牛胚胎的发育和存活，从而在血浆尿素氮浓度升高和繁殖力降低之间提供了一个合理的联系。高产奶牛繁殖力差反映了子宫环境的综合影响，子宫环境依赖孕酮，因负能量平衡或产后健康问题的前期影响而变得不理想，并且因高日粮蛋白质摄入产生的尿素影响而进一步受损。
