Animal performance and sward characteristics of two cultivars of Brachiaria brizantha (BRS Paiaguás and BRS Piatã)

ABSTRACT The objective of the present study was to evaluate live weight gain per animal and per area and its relationship with the characteristics of pastures of Brachiaria brizantha cv. Paiaguás and Piatã. A randomized blocks experimental design was used, with two treatments and six replicates. The experimental area was 8.0 ha, divided into twelve paddocks of 0.67 ha. The grazing method used was continuous stocking, with variable stocking rate. Three tester steers were used per paddock. Sward heights were measured once a week, and the stocking rate (SR) was adjusted using regulator steers to maintain the sward height at 30 cm. Pasture samples were collected once a month, and herbage accumulation rate (HAR), percentage of leaves (PL), leaf:stem ratio (LSR), and nutritive value (NV) were determined. Animals were weighed every 28 days. No differences between the two cultivars were observed during the wet season for any of the evaluated parameters. However, cv. Paiaguás presented higher HAR and, consequently, higher SR than cv. Piatã during the dry season. As a result of its higher regrowth, cv. Paiaguás pastures presented significantly higher PL, LSR, and NV and, consequently, significantly higher average daily live weight gain. These differences resulted in higher live weight gain per area for Paiaguás grass (695 kg/ha per year) than for Piatã grass (645 kg/ha per year). Thus, Brachiaria brizantha cv. Paiaguás is a good alternative to decrease the temporary forage shortage and for the diversification of pastures in the Cerrado biome region.摘要 本研究旨在评估单头家畜及单位面积的活体增重，并分析其与布氏臂形草（Brachiaria brizantha）品种Paiaguás和Piatã牧地特征的关联。本研究采用随机区组试验设计，设置2个处理组，6次重复。试验区域总面积为8.0公顷，划分为12个面积0.67公顷的放牧小区。放牧方式采用可变载畜率的连续放牧制度，每个放牧小区投放3头试验阉牛。每周测定1次草层高度，通过调节对照阉牛的数量调整载畜率（stocking rate, SR），以维持草层高度稳定在30 cm。每月采集1次牧草样品，测定牧草累积速率（herbage accumulation rate, HAR）、叶片占比（percentage of leaves, PL）、叶茎比（leaf:stem ratio, LSR）及营养价值（nutritive value, NV）。每28天对试验家畜进行1次称重。雨季阶段，两个品种的所有被测参数均未观测到显著差异。但在旱季，Paiaguás品种的牧草累积速率更高，对应的载畜率也显著高于Piatã品种。得益于更强的再生能力，Paiaguás牧地的叶片占比、叶茎比及营养价值均显著提升，平均日增重也随之显著升高。上述差异使得Paiaguás牧地的单位面积年活体增重为695 kg/ha，高于Piatã牧地的645 kg/ha。综上，布氏臂形草（Brachiaria brizantha）品种Paiaguás可作为缓解塞拉多生物群系（Cerrado biome）区域暂时性牧草短缺、丰富牧地多样性的优良备选方案。