Tyrrell H F, Thomson D J, Waldo D R, Goering H K, Haaland G L
Ruminant Nutrition Laboratory, Livestock and Poultry Science Institute, ARS, USDA, Beltsville, MD 20705.
J Anim Sci. 1992 Oct;70(10):3163-77. doi: 10.2527/1992.70103163x.
First-growth orchardgrass and alfalfa were harvested at two stages of maturity, treated with formic acid plus formaldehyde, and ensiled as direct-cut silage during 1978 and 1979. The 1978 silages were fed to eight yearling Holstein heifers (average BW 273 kg), and the 1979 silages were fed to eight yearling Holstein steers (average BW 264 kg) in replicated 4 x 4 Latin square experiments to measure total energy and N balance using the Beltsville open-circuit respiration calorimeters. Silage was offered daily at 70 g of DM/kg.75 BW, a rate that was essentially ad libitum for late-maturity orchardgrass, but restricted for the other three silages within each experiment. Cattle fed alfalfa used ME for growth with greater efficiency (55%) than did cattle fed orchardgrass (40%). Cattle fed orchardgrass achieved the same tissue N retention at a lower total N intake than did cattle fed alfalfa. Differences in tissue N retention were accounted for by differences in N intake insoluble in autoclaved ruminal fluid, but soluble in acid detergent, a fraction termed available N. At equal intake of ME and available N, cattle fed alfalfa gained more tissue energy than those fed orchardgrass and gained tissue protein similarly to cattle fed orchardgrass. Fractions composing digestible OM were different between forage types but similar within forage type between maturities at harvest. More efficient use of ME for growth by animals fed alfalfa compared with orchardgrass may be related to differences in digestible OM composition, load of digestive tract content, and composition of absorbed nutrients.
一级生长的果园草和苜蓿在两个成熟阶段进行收割，用甲酸加甲醛处理，并在1978年和1979年作为直接切割青贮饲料进行青贮。1978年的青贮饲料喂给了8头一岁的荷斯坦小母牛（平均体重273千克），1979年的青贮饲料喂给了8头一岁的荷斯坦阉牛（平均体重264千克），在重复的4×4拉丁方实验中，使用贝尔茨维尔开路呼吸热量计测量总能量和氮平衡。每天以70克干物质/千克·0.75体重的量提供青贮饲料，对于晚熟果园草来说，这个量基本上是随意采食的，但在每个实验中，对其他三种青贮饲料来说是限量的。与饲喂果园草的牛（40%）相比，饲喂苜蓿的牛将代谢能用于生长的效率更高（55%）。饲喂果园草的牛在总氮摄入量较低的情况下，实现了与饲喂苜蓿的牛相同的组织氮保留。组织氮保留的差异是由高压灭菌瘤胃液中不溶但酸洗涤剂中可溶的氮摄入量差异造成的，这一部分称为可利用氮。在代谢能和可利用氮摄入量相等的情况下，饲喂苜蓿的牛比饲喂果园草的牛获得了更多的组织能量，并且获得的组织蛋白质与饲喂果园草的牛相似。不同饲草类型之间构成可消化有机物质的组分不同，但在收获时同一饲草类型内不同成熟度之间相似。与果园草相比，饲喂苜蓿的动物将代谢能更有效地用于生长，这可能与可消化有机物质组成、消化道内容物负荷以及吸收养分组成的差异有关。
