Feed intake and liveweight responses to nitrogen and/or protein supplements by steers of Bos taurus, Bos indicus and Bos taurus × Bos indicus breed types offered a low quality grass hay
Feed intake and liveweight responses to nitrogen and/or protein supplements by steers of Bos taurus, Bos indicus and Bos taurus × Bos indicus breed types offered a low quality grass hay
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金牛牛、印度牛和牛 × 印度牛品种类型提供低品质干草的阉牛的采食量和活重对氮和/或蛋白质补充剂的反应
DOI：
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发表时间：
2000
影响因子：
0.6
通讯作者：
R. Darnell
中科院分区：
文献类型：
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作者：
D. Hennessy;P. Williamson;R. Darnell
在两个围栏实验（实验1和2），其中27个在第三个（实验3），用30只阉牛，以量化他们的干草摄入量，瘤胃氨态氮（RAN）浓度和活重的瘤胃可溶性氮（尿素）和瘤胃不可降解蛋白质（甲醛处理的酪蛋白，F-酪蛋白）的输入时，添加到基础日粮的低品质干草的反应。干草由未改良的天然牧草制成，这些牧草是澳大利亚亚热带牛放牧的典型牧草，试验1和2中含有7.8 g N/kg干物质（DM），有机物消化率系数为0.503，试验3中含有5.2 g N/kg DM，消化率范围为0.385至0.448。阉牛（15个月大）是婆罗门（B）、赫里福德（H）或F1婆罗门×赫里福德（BH）杂交牛。在每个实验中，牛都被提供了补充矿物质和干草。在实验1（35天）尿素喷洒部分干草，允许每日尿素摄入量（克/牛）为0，5，11，16或26。在实验2（42天）中，每天提供0、75、150、225或300（g/牛）的F-酪蛋白，在实验3（56天）中，不连续提供可溶性酪蛋白（225 g/天）、尿素（18 g/天）+F-酪蛋白（225 g/天）或零。尿素采食量对肉牛干草采食量和体重变化有显著的线性影响。然而，B阉牛有较小的增加摄入量和活重变化比H阉牛，和B阉牛没有一个线性增加RAN浓度增加尿素摄入量的H和BH阉牛。在实验2中，有显着的线性效应的F-酪蛋白补充干草摄入量和活重变化的阉牛和显着改善其饲料转化率（即DM摄入量：活重变化）。B牛与H和BH牛在活重变化方面没有差异，但随着F-酪蛋白摄入量的增加，干草摄入量显着降低，RAN增加不显着。试验3中，添加可溶性酪蛋白和尿素+F-酪蛋白的肉牛干草采食量分别增加了16.8%和24.5%。只有给予尿素+F-酪蛋白的阉牛具有高RAN浓度（94 mg/l）和高增重。试验3中，B牛的活重损失和干草采食量低于H或BH牛，但RAN浓度高于H或BH牛。这些研究表明，提供低氮、低消化率干草时，不同品种类型的牛需要额外的氮的形式和数量，以优化其采食量和增重。
Thirty steers were used in two pen experiments (Expts 1 and 2), and 27 of these in a third (Expt 3), to quantify their responses of hay intake, rumen ammonia nitrogen (RAN) concentrations, and liveweight to inputs of rumen soluble nitrogen (urea) and rumen undegradable protein (formaldehyde-treated casein; F-casein) when added to a basal diet of low quality hays. The hays were made from unimproved native pastures typical of those grazed by cattle in the subtropics of Australia and contained 7·8 g N/kg dry matter (DM) with coefficient of organic matter digestibility of 0·503 in Expts 1 and 2, and 5·2 g N/kg DM with a digestibility range from 0·385 to 0·448 in Expt 3. The steers (15 months old) were either Brahman (B), Hereford (H) or the F1 Brahman×Hereford (BH) cross. Steers were offered supplementary minerals with the hays in each experiment. In Expt 1 (35 days) urea was sprayed on part of the hay, allowing for daily urea intakes (g/steer) of either 0, 5, 11, 16 or 26. In Expt 2 (42 days), F-casein was offered daily (g/steer) at either 0, 75, 150, 225 or 300 and in Expt 3 (56 days) discrete offerings were made of soluble casein (225 g/day), of urea (18 g/day)+F-casein (225 g/day) or of nil. There were significant linear effects of urea intake upon hay intake and liveweight change of steers. However, B steers had smaller increases in intake and liveweight change than did H steers, and B steers did not have a linear increase in RAN concentrations with increasing urea intake as did H and BH steers. In Expt 2 there were significant linear effects of F-casein supplements on hay intake and liveweight change of steers and a significant improvement in their feed conversion ratio (i.e. DM intake: liveweight change). The B steers did not differ from H and BH steers in liveweight change but had significantly lower hay intakes and non-significantly smaller increases in RAN with increasing F-casein intake. In Expt 3, hay intake of the steers increased with soluble casein (by 16·8%) and with urea+F-casein (24·5%). Only steers given urea+F-casein had a high RAN concentration (94 mg/l) and a high liveweight gain. The B steers had a liveweight loss and a lower hay intake than H or BH steers in Expt 3 but a higher RAN concentration. These studies have indicated the importance of the form and quantity of additional N required by cattle of differing breed types to optimize their feed intake and liveweight gain when offered low-N, low-digestible hays.