Department of Animal Science, Division of Agriculture, University of Arkansas, Fayetteville, USA.
J Anim Sci. 2011 Nov;89(11):3824-30. doi: 10.2527/jas.2010-3725. Epub 2011 Jun 3.
Two complementary experiments were completed to assess short-term foraging dynamics, diet quality, and ruminal degradation kinetics of herbage consumed by steers with 3 levels of herbage depletion. Experiment 1 was a behavioral study in which 2 ruminally cannulated steers were allocated to grazing scenarios simulating 3 levels of herbage depletion. These treatments included an ungrazed sward (control), as well as medium and high levels of herbage depletion. Grazing scenarios were sampled for sward surface height and amount of green leaf and stem before being grazed. Foraging dynamics were determined through measurements of bite rate, bite depth, eating step rate, eating distance, potential area consumed while grazing, and bites and intake per eating step. Also, quality of potential herbage consumed was estimated from hand-plucked herbage. In Exp. 2, ruminal degradation kinetics of DM for samples of herbage consumed (masticate) by steers during Exp. 1 were assessed in situ using 5 ruminally cannulated steers. The immediately soluble, degraded, and undegraded DM fractions were determined. The DM disappearance rate and lag times were determined from a nonlinear regression model, and the effective degradability of DM was calculated. Herbage depletion resulted in increased eating steps/minute, as well as the potential area harvested while grazing (P < 0.05) and reduced herbage intake/eating step (P < 0.05). Neither the herbage potentially consumed nor the ruminal degradation kinetics was affected by extent of depletion (P > 0.05). Under these experimental conditions, steers adapted their foraging dynamic and were able to sustain diet quality in the short term. These results imply that behavioral adaptations would make diet quality less sensitive to certain levels of herbage depletion.
进行了两项互补实验，以评估处于 3 个牧草耗竭水平的肉牛的短期觅食动态、日粮质量和瘤胃牧草降解动力学。实验 1 是一项行为研究，其中 2 头瘤胃插管的肉牛被分配到模拟 3 个牧草耗竭水平的放牧场景中。这些处理包括未放牧的草地（对照）以及中等和高水平的牧草耗竭。在放牧前，对放牧场景进行了采样，以测量草丛表面高度和绿叶与茎的数量。通过测量咬率、咬深、进食步速、进食距离、放牧时潜在的采食面积以及每进食步的咀嚼和摄入量，确定了觅食动态。此外，还从手拔草中估计了潜在牧草的质量。在实验 2 中，使用 5 头瘤胃插管的肉牛，对实验 1 期间肉牛采食（咀嚼）的牧草样本的瘤胃降解动力学进行了原位评估。确定了立即可溶、降解和未降解的 DM 分数。通过非线性回归模型确定 DM 消失率和滞后时间，并计算 DM 的有效降解率。牧草耗竭导致进食步/min 增加，以及放牧时潜在的采食面积增加（P <0.05），而采食/进食步减少（P <0.05）。牧草的潜在消耗量和瘤胃降解动力学都不受耗竭程度的影响（P >0.05）。在这些实验条件下，肉牛适应了它们的觅食动态，并能够在短期内维持日粮质量。这些结果表明，行为适应会使日粮质量对某些水平的牧草耗竭不那么敏感。
