Poppi D P, McLennan S R
Department of Agriculture, University of Queensland, Brisbane, Australia.
J Anim Sci. 1995 Jan;73(1):278-90. doi: 10.2527/1995.731278x.
Low live weight gain of cattle in the wet season of tropical areas was identified as a major limitation to achieving annual growth rates from tropical pasture systems sufficient to meet new market specifications of young animals of high carcass weight. Both protein and energy are limiting nutrients for growth. Net transfer of feed protein to the intestines is often not complete, and losses occur with grasses and legumes when CP content exceeds 210 g of CP/kg of digestible OM. This protein loss is important because a collation of experimental data indicated that cattle consuming low- and high-quality pasture and silage-based diets all responded to extra protein. The response was less for the higher-quality forage. The role of legumes in supplying this protein was investigated and, unless legumes can increase total DMI by at least 30%, they will not supply sufficient intestinal protein to increase live weight gain by about 300 g/d. The problem with legumes and some grasses is the loss of protein from the rumen, and increasing energy supply to the rumen, either through improved digestibility or energy supplements, is a strategy that could be used to reduce this. Strategies to increase the proportion of escape protein would be successful, but incorporation of lowly degradable protein fractions into legumes may be more difficult because of the level of expression of these protein fractions required for a significant live weight gain response. Cattle entering the wet season usually exhibit compensatory growth and are exposed to high ambient temperatures and often to high humidity. Intestinal protein above that stipulated in feeding standards may be beneficial in these circumstances, and more emphasis should be placed on the ability of legumes to supply protein postruminally. At present the protein delivery capacity of agronomically competitive legumes seems to be inadequate for the higher growth rates required in production systems, and supplements of energy and protein will be needed to achieve these higher targets until new cultivars appear.
热带地区雨季牛的低体重增长被认为是实现热带牧场系统年增长率的主要限制因素，该增长率要足以满足新的高胴体重幼畜市场规格。蛋白质和能量都是生长的限制营养素。饲料蛋白质向肠道的净转移通常不完全，当粗蛋白含量超过每千克可消化有机物质210克粗蛋白时，禾本科牧草和豆科植物都会出现损失。这种蛋白质损失很重要，因为一系列实验数据表明，食用低质量和高质量牧场及青贮饲料日粮的牛都对额外蛋白质有反应。对于高质量牧草，反应较小。研究了豆科植物在提供这种蛋白质方面的作用，除非豆科植物能使总干物质摄入量至少增加30%，否则它们将无法提供足够的肠道蛋白质来使体重增加约300克/天。豆科植物和一些禾本科牧草的问题在于瘤胃中蛋白质的损失，通过提高消化率或添加能量补充剂来增加瘤胃能量供应是一种可以用来减少这种损失的策略。增加过瘤胃蛋白质比例的策略会成功，但由于显著的体重增加反应所需的这些蛋白质组分的表达水平，将低降解蛋白质组分掺入豆科植物可能更困难。进入雨季的牛通常表现出补偿性生长，并且暴露于高环境温度且常常是高湿度环境中。在这些情况下，高于饲养标准规定的肠道蛋白质可能是有益的，并且应该更加强调豆科植物在瘤胃后提供蛋白质的能力。目前，从农艺学角度具有竞争力的豆科植物的蛋白质供应能力似乎不足以满足生产系统所需的更高生长速度，在新的品种出现之前，需要补充能量和蛋白质来实现这些更高的目标。
