Scholljegerdes E J, Ludden P A, Hess B W
Department of Animal Science, University of Wyoming, Laramie, WY 82071-3684, USA.
J Anim Sci. 2004 Apr;82(4):1146-56. doi: 10.2527/2004.8241146x.
Eight Angus x Gelbvieh heifers (445 +/- 74.5 kg) fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square double double-crossover designed experiment to assess the effect of restricted forage intake on site and extent of digestion and flow of essential AA amino acids to the small intestine. Heifers were fed chopped (2.54 cm) bromegrass hay (9.2% CP, 64% NDF on an OM basis) at one of four percentages of maintenance (30, 60, 90, and 120%). Experimental periods were 21 d in length, with 17 d of adaptation followed by 4 d of intensive sample collection, after which maintenance requirements and subsequent level of intake were adjusted for BW change. True ruminal OM, NDF, and N digestion (g/d) decreased linearly (P < 0.001) with decreasing forage intake. When expressed as a percentage of OM intake, true ruminal OM and N digestibility were not affected (P = 0.23 to 0.87), whereas ruminal NDF digestibility tended to increase (P = 0.09) as forage intake decreased. Total and microbial essential amino acid flow to the duodenum decreased linearly (P = 0.001) from 496.1 to 132.1 g/d and 329.1 to 96.0 g/d, as intake decreased from 120 to 30% of maintenance intake, respectively. Although the profile of individual essential amino acids in duodenal digesta (P = 0.001 to 0.07) and isolated ruminal microbes differed (P = 0.001 to 0.09) across treatment, the greatest difference noted for total and microbial essential amino acid profile was only 0.3 percentage units. Because total and microbial flow of essential amino acids to the small intestine decreased as OM intake decreased, but true ruminal degradability of individual essential amino acids (P = 0.17 to 0.99) and digesta essential amino acid profile were comparable across treatments, total essential amino acid supply to the small intestine was predicted using OM intake as the independent variable. The resulting simple linear regression equation was: total essential amino acid flow = (0.055 x OM intake) + 1.546 (r2 = 0.91). The model developed in this experiment accounted for more of the variation in the data set than the current beef cattle NRC model, which under-predicted total flow of essential amino acids to the duodenum. The prediction equation developed herein can be used to estimate the supply of essential amino acids reaching the small intestine when formulating supplements to compensate for potential amino acid deficiencies resulting from restricted forage intake.
选用8头安格斯×盖尔维杂交小母牛（体重445±74.5千克），安装瘤胃和十二指肠瘘管，进行4×4拉丁方双交叉设计试验，以评估限制粗饲料采食量对消化部位、消化程度以及必需氨基酸向小肠流动的影响。小母牛饲喂切碎（2.54厘米）的雀麦干草（以干物质计，粗蛋白含量9.2%，中性洗涤纤维含量64%），采食量分别为维持需要量的4个水平（30%、60%、90%和120%）。试验期为21天，其中17天为适应期，随后4天为强化样本采集期，之后根据体重变化调整维持需要量和后续采食量水平。随着粗饲料采食量的降低，瘤胃中干物质、中性洗涤纤维和氮的真消化量（克/天）呈线性下降（P<0.001）。以干物质采食量的百分比表示时，瘤胃中干物质和氮的真消化率不受影响（P=0.23至0.87），而随着粗饲料采食量的降低，瘤胃中性洗涤纤维消化率呈上升趋势（P=0.09）。随着采食量从维持需要量的120%降至30%，进入十二指肠的总必需氨基酸和微生物必需氨基酸流量分别从496.1克/天线性下降至132.1克/天，从329.1克/天线性下降至96.0克/天（P=0.001）。尽管不同处理间十二指肠食糜中单个必需氨基酸的组成（P=0.001至0.07）和瘤胃分离微生物中单个必需氨基酸的组成存在差异（P=0.001至0.09），但总必需氨基酸和微生物必需氨基酸组成的最大差异仅为0.3个百分点。由于随着干物质采食量的降低，进入小肠的必需氨基酸总流量和微生物流量均下降，但各处理间单个必需氨基酸的瘤胃真降解率（P=0.17至0.99）和食糜必需氨基酸组成相当，因此以干物质采食量作为自变量预测进入小肠的必需氨基酸总供应量。得到的简单线性回归方程为：必需氨基酸总流量=（0.055×干物质采食量）+1.546（r2=0.91）。本试验建立的模型比当前肉牛营养需要量委员会（NRC）模型能解释更多数据集中的变异，NRC模型对进入十二指肠的必需氨基酸总流量预测偏低。本文建立的预测方程可用于在配制补充料时估计进入小肠的必需氨基酸供应量，以弥补因粗饲料采食量受限可能导致的氨基酸缺乏。
