Department of Animal Sciences, Universidade Federal de Lavras, Lavras, Minas Gerais, Brazil.
Embrapa Agrobiologia, Rodovia, Seropédica, Rio de Janeiro, Brazil.
J Anim Sci. 2018 Sep 7;96(9):3837-3849. doi: 10.1093/jas/sky236.
Maintenance of mixed grass-legume pastures for stand longevity and improved animal utilization is a challenge in warm-season climates. The goal of this study was to assess grazing management on stand persistence, forage intake, and N balance of beef heifers grazing mixed pastures of Brachiaria brizantha and Arachis pintoi. A 2-yr experiment was carried out in Brazil, where four grazing management were assessed: rest period interrupted at 90%, 95%, and 100% of light interception (LI) and a fixed rest period of 42 d (90LI, 95LI, 100LI, and 42D, respectively). The LI were taken at 50 points at ground level and at 5 points above the canopy for each paddock using a canopy analyzer. For all treatments, the postgrazing stubble height was 15 cm. Botanical composition and canopy structure characteristics such as canopy height, forage mass, and vertical distribution of the morphological composition were evaluated pre- and post-grazing. Forage chemical composition, intake, and microbial synthesis were also determined. A randomized complete block design was used, considering the season of the year as a repeated measure over time. Grazing management and season were considered fixed, while block and year were considered random effects. In the summer, legume mass accounted for 19% of the canopy at 100LI, which was less than other treatments (a mean of 30%). The 100LI treatment had a greater grass stem mass compared with other treatments. In terms of vertical distribution for 100LI, 38.6% of the stem mass was above the stubble height, greater than the 5.7% for other treatments. The canopy structure limited NDF intake (P = 0.007) at 100LI (1.02% of BW/d), whereas 42D, 90LI, and 95LI treatments had NDF intake close to 1.2% of BW/d. The intake of digestible OM (P = 0.007) and the ratio of CP/digestible OM (P < 0.001) were less at 100LI in relation to the other treatments. The production of microbial N (P < 0.001) and efficiency of microbial synthesis (P = 0.023) were greater at 95LI and 90LI, followed by 42D and less at 100LI. Overall, the range from 90% to 95% of LI is the recommendation to interrupt the rest period, since this strategy enhanced community stability, forage intake, and nutritional value of the diet. Under on-farm conditions, brachiaria grass and forage peanut pastures should be managed at a range height of 24 to 30 cm.
在暖季气候条件下，为了保持混播禾本科-豆科牧草的持久性和提高动物的利用率，需要对其进行维护。本研究的目的是评估放牧管理对混播草地持久性、饲草采食量和肉牛采食混播百喜草和花生地雀稗草地的氮平衡的影响。本试验在巴西进行了 2 年，评估了 4 种放牧管理方式：在光截获率（LI）的 90%、95%和 100%时打断休牧期，以及 42 天固定休牧期（分别为 90LI、95LI、100LI 和 42D）。利用冠层分析仪在每个围栏的地面水平处的 50 个点和树冠上方 5 个点测量 LI。所有处理的放牧后残茬高度均为 15 厘米。在放牧前后评估了植物群落组成和冠层结构特征，如冠层高度、饲草质量和形态组成的垂直分布。还测定了饲草的化学成分、采食量和微生物合成。采用随机完全区组设计，将一年中的季节作为时间重复的衡量标准。放牧管理和季节被认为是固定的，而区组和年份被认为是随机的。在夏季，100LI 的豆科牧草质量占冠层的 19%，低于其他处理（平均为 30%）。100LI 处理的草茎质量大于其他处理。就 100LI 的垂直分布而言，38.6%的茎质量高于残茬高度，高于其他处理的 5.7%。冠层结构限制了 NDF 采食量（P = 0.007），在 100LI 时（占 BW/d 的 1.02%），而 42D、90LI 和 95LI 处理的 NDF 采食量接近 BW/d 的 1.2%。可消化 OM 的采食量（P = 0.007）和 CP/可消化 OM 的比例（P < 0.001）在 100LI 时低于其他处理。微生物 N 的产量（P < 0.001）和微生物合成效率（P = 0.023）在 95LI 和 90LI 时较高，其次是 42D，而在 100LI 时较低。总的来说，LI 的 90%到 95%范围内是打断休牧期的推荐范围，因为这种策略增强了群落的稳定性、饲草的采食量和日粮的营养价值。在农场条件下，百喜草和花生地雀稗草地应管理在 24 到 30 厘米的高度。
