Different true-protein sources do not modify the metabolism of crossbred Bos taurus × Bos indicus growing heifers

The present study was conducted to investigate the effect of alternative true-protein sources to soybean meal, with different ruminal degradability, using a sugarcane-based diet, on nutrient digestion, ruminal fermentation, efficiency of microbial protein synthesis and passage rate in prepubertal dairy heifers. Eight crossbred rumen- and duodenum-cannulated Holstein × Gyr dairy heifers (202.0±11.5 kg BW) were evaluated in a 4 × 4 Latin square experimental design with four treatments and four periods in two simultaneous replicates. Dietary treatments were: soybean meal; cottonseed meal; peanut meal; and sunflower meal. When associated with diets containing sugarcane, the different protein sources did not affect intake or digestibility of dry mater, crude protein, organic matter and neutral detergent fiber. The average ruminal pH, NH3-N and concentration of total volatile fatty acids were not different among the diets supplied. The concentration of butyric acid was different among the protein sources, wherein the animals fed the diet with sunflower meal presented lower values than those fed the other sources. Diets did not affect nitrogen balance, microbial nitrogen, microbial synthesisefficiency, estimated dry matter flow, or passage rate. Alternative protein sources can be used to reduce the costs without changing the animal metabolism.

本研究旨在探究以甘蔗为基础日粮时，不同瘤胃降解特性（ruminal degradability）的替代真蛋白源替代豆粕（soybean meal），对青春期前奶牛青年母牛的营养物质消化率、瘤胃发酵、微生物蛋白质合成效率及流通速率的影响。本试验采用4×4拉丁方实验设计，设置4个处理组与4个试验周期，分2个平行重复，共选用8头安装有瘤胃及十二指肠瘘管的荷斯坦×吉尔（Holstein × Gyr）杂交奶牛青年母牛，初始体重为202.0±11.5 kg。日粮处理组分别为：豆粕、棉籽粕（cottonseed meal）、花生粕（peanut meal）及葵花籽粕（sunflower meal）。在搭配甘蔗日粮的条件下，不同蛋白源对干物质（dry matter）、粗蛋白质（crude protein）、有机物（organic matter）及中性洗涤纤维（neutral detergent fiber）的采食量与消化率均无显著影响。各组日粮的平均瘤胃pH值、氨态氮（NH₃-N）浓度及总挥发性脂肪酸（volatile fatty acids）浓度均无显著差异。不同蛋白源日粮的丁酸浓度存在显著差异，其中饲喂葵花籽粕日粮的试验牛丁酸浓度显著低于饲喂其他蛋白源日粮的个体。日粮对氮平衡、微生物氮（microbial nitrogen）含量、微生物合成效率、估算干物质流通量及流通速率均无显著影响。采用替代蛋白源可降低饲养成本，且不会改变动物的代谢机能。