Supplementation of growing bulls grazing Panicum maximum cv. Coloniao increases average daily gain and does not impact subsequent performance in feedlot phase

ABSTRACT To evaluate the influence of supplementation strategies on the average daily gain (ADG) of cattle in a rotational grazing system of Guinea grass (Panicum maximum cv. Coloniao) pastures during the rainy season. It was further evaluated the residual effects in the feedlot finishing phase. Seventy-five 8 month-old crossbred bull calves averaging 200.1 ± 2.5 kg of body weight (BW) were stratified and grouped in three into 25 blocks according to BW, and then randomly assigned to one of three supplementation treatments: control (no supplement), energy supplement [65 g crude protein (CP)/kg dry matter (DM)] or protein supplement (200 g CP/kg DM) both fed as 6 g/kg BW. All animals composed a single herd and were separated daily according to treatment groups for supplementation. After the grazing phase, all animals were moved to a feedlot and received the same diet up until slaughter. Guinea grass was subjected to rotational stocking with pre- and post-grazing heights of 76 and 43 cm, respectively. Energy and protein supplements provided similar ADG (P > 0.05; 0.94 kg/day) which was greater than for non-supplemented animals during the grazing phase (P ≤ 0.05; 0.74 kg/day), but there was no difference in the subsequent feedlot phase (P > 0.05; 1.45 kg/day). The protein supplement had no incremental effects over the energy supplement on ADG and carcass traits of growing crossbreed bulls during the grazing phase, indicating that either source could be used, and that an energy supplement would lead to more efficient nutrient use coming from the grass.摘要 本试验旨在评估雨季期间，Coloniao品种大黍草（Panicum maximum cv. Coloniao）轮牧牧场中补饲策略对肉牛平均日增重（average daily gain, ADG）的影响，并进一步探究其在育肥舍育肥阶段的后续效应。试验选取75头8月龄杂交肉牛犊，初始体重为200.1±2.5 kg，按体重分层划分为25个区组，每区组3头，随后随机分配至3种补饲处理组：对照组（无补饲）、能量补饲组[干物质（dry matter, DM）基础含65 g粗蛋白（crude protein, CP）]或蛋白质补饲组（DM基础含200 g CP），补饲剂量均为6 g/kg体重。所有试验动物组成同一牧群，每日按处理组分开进行补饲。放牧阶段结束后，所有动物转至育肥舍，饲喂相同日粮直至屠宰。供试牧草采用轮牧制度，放牧前、后高度分别为76 cm与43 cm。放牧阶段，能量补饲组与蛋白质补饲组的平均日增重无显著差异（P>0.05；0.94 kg/天），且均显著高于对照组（P≤0.05；0.74 kg/天）；但后续育肥阶段各组间无显著差异（P>0.05；1.45 kg/天）。放牧阶段，蛋白质补饲相较于能量补饲对杂交肉牛犊的平均日增重及胴体性状无额外增益效果，表明两类补饲源均可使用，且能量补饲可更高效地利用牧草中的营养物质。