Context Cattle grazing tropical forages usually perform below genetic potential due to limited nutrient intake. Aims Four experiments were conducted to evaluate supplementation strategies on performance and metabolism of cattle grazing intensively managed marandu palisade grass (Urochloa brizantha). Methods Experiment 1 evaluated the average daily gain (ADG) of 72 young bulls (222 ± 25 kg bodyweight, BW) grazing palisade grass and supplemented (22% crude protein, CP) at 0.0%, 0.3%, 0.6% and 0.9% BW, and their ADG during the feedlot finishing phase. Experiment 2 evaluated the ADG of 80 bulls (240 ± 18 kg BW) grazing palisade grass and supplemented with energy (11.3% CP) or three protein sources (≈20.5% CP) at 0.6% BW. Experiment 3 investigated intake, rumen parameters and digestibility of nutrients in fistulated steers (410 ± 8.6 kg BW) fed an energy supplement, that is, ground corn, at 0.0%, 0.3%, 0.6% and 0.9% BW, with a parallel in vitro study of fermentation kinetics (Experiment 4). Key results Increased levels of supplementation resulted in linear increases (P 0.05) in ADG, SR and BW gain per area among supplemental sources of protein or the energy supplement. Increasing energy levels caused a linear decrease (P 0.05) fibre degradability. Corn supplementation also caused a linear decrease (P < 0.05) in acetate : propionate ratio, in ruminal ammonia-N and in N excretion, and a linear increase (P < 0.05) in rumen propionate concentration, in microbial synthesis and in N retention. The supplementation increased BW at the start of the feedlot phase, resulting in similar hot carcass weights with fewer days on feed and no effects on meat quality. Conclusions Overall, despite the source utilised, supplementation increased ADG, SR and BW gain per area, with fewer days being required on the finishing period. Implications Having adequate supplementation strategies in place will help producers increase the efficiency of their systems.

中文翻译：

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在热带牧场上战略性地补充养牛可改善养分利用率和动物性能，减少育肥阶段所需的天数

背景 由于营养摄入有限，放牧热带草料的牛通常表现低于遗传潜力。目的 进行了四项实验，以评估对集中管理的马兰杜栅栏草 (Urochloa brizantha) 放牧的牛的性能和代谢的补充策略。方法 实验 1 评估了 72 头年轻公牛（222 ± 25 kg 体重，BW）放牧栅栏草和补充（22% 粗蛋白，CP）0.0%、0.3%、0.6% 和 0.9% BW 的平均日增重（ADG） ，以及它们在饲养场育肥阶段的 ADG。实验 2 评估了 80 头公牛 (240 ± 18 kg BW) 放牧栅栏草并补充能量 (11.3% CP) 或三种蛋白质来源 (≈20.5% CP) 0.6% BW 的 ADG。实验 3 研究了瘘管 (410 ± 8. 6 kg BW) 饲喂能量补充剂，即 0.0%、0.3%、0.6% 和 0.9% BW 的磨碎玉米，同时进行发酵动力学的平行体外研究（实验 4）。主要结果 在补充蛋白质或能量补充来源中，增加补充水平导致单位面积的 ADG、SR 和 BW 增加线性增加（P = 0.05）。增加能级导致纤维降解性线性下降 (P 0.05)。玉米补充还导致乙酸：丙酸比、瘤胃氨氮和 N 排泄线性降低（P < 0.05），瘤胃丙酸浓度、微生物合成和 N 保留线性增加（P < 0.05）。在饲养场阶段开始时，补充剂增加了体重，导致相似的热屠体重量，饲料天数减少，对肉质没有影响。结论 总体而言，尽管使用了源，但补充剂增加了每个区域的 ADG、SR 和 BW 增益，并且在育肥期所需的天数更少。影响 制定适当的补充策略将有助于生产者提高其系统的效率。