Gekara O J, Prigge E C, Bryan W B, Nestor E L, Seidel G
Division of Animal and Veterinary Sciences, West Virginia University, Morgantown, 26506-6108, USA.
J Anim Sci. 2005 Jun;83(6):1435-44. doi: 10.2527/2005.8361435x.
To establish the effect of sward height, concentrate feeding time, and restricted time for grazing on forage utilization by grazing cattle, 32 crossbred beef (24 Angus and eight Hereford) cows (632 kg BW) and calves (104 kg BW) were grouped by weight and calving date. They were assigned randomly to two sward height treatments (4 to 8 or 8 to 12 cm), replicated four times. The herbage comprised mainly Kentucky bluegrass, orchardgrass, some forbs, and white clover. The cows were restricted to 12 h/d grazing (0700 to 1900) or unrestricted to 24 h/d grazing and fed a concentrate supplement (4.1 kg DM.cow(-1).d(-1), approximately 0.65% of BW or 33% of total DMI) either at 0700 or 1800. The experiment was repeated over three 15-d periods in May, June/July, and August 2000. The herbage on high sward height pasture was higher (P = 0.06) in NDF and ADF and lower (P < 0.01) in CP than low sward height herbage. For cows restricted to 12 h/d grazing, supplementing at 0700 as opposed 1800 resulted in greater (P = 0.04) forage DMI (8.6 vs. 8.1 kg/d), whereas cows that were unrestricted showed little change (8.2 kg/d at 0700 vs. 8.4 kg/d at 1800). Supplementing at 1800 as opposed to 0700 resulted in greater (P = 0.03) herbage DM digestibility (67.7 vs. 64.5%) for cows on high sward height, whereas cows on low sward height exhibited minimal differences (65.4% at 1800 vs. 66.3% at 0700). Cows restricted to 12 h/d grazing and supplemented at 0700 as opposed to 1800 resulted in greater (P = 0.06) digestible DMI (5.0 vs. 4.7 kg/d), whereas unrestricted cows exhibited the opposite response (4.6 kg/d digestible DMI at 0700 vs. 4.9 kg/d at 1800). Supplementing at 1800 as opposed to 0700 increased the time spent grazing to a greater (P = 0.09) extent for restricted than for unrestricted cows. When forage availability or grazing time was limiting (due to a low forage allowance and restricted access to forage, respectively) supplementing concentrates at 0700 resulted in greater forage utilization and intake rate because of increased forage DMI, DM digestibility, and digestible DMI. However, when forage or grazing time was not limiting, supplementing concentrates at 1800 resulted in greater forage utilization because of increased forage DM digestibility.
为确定草层高度、精料补饲时间和放牧限制时间对放牧母牛饲草利用率的影响，按体重和产犊日期将32头杂交肉牛（24头安格斯牛和8头赫里福德牛）母牛（体重632千克）和犊牛（体重104千克）进行分组。将它们随机分配到两种草层高度处理组（4至8厘米或8至12厘米），重复4次。牧草主要由草地早熟禾、鸭茅、一些杂草和白三叶组成。母牛每天限制放牧12小时（07:00至19:00）或不限制放牧24小时，并在07:00或18:00补饲精料（4.1千克干物质·母牛⁻¹·天⁻¹，约占体重的0.65%或总干物质采食量的33%）。该试验在2000年5月、6月/7月和8月的三个15天周期内重复进行。高草层高度牧场的牧草中性洗涤纤维和酸性洗涤纤维含量较高（P = 0.06），粗蛋白含量较低（P < 0.01），比低草层高度的牧草低。对于每天限制放牧12小时的母牛，07:00补饲而非18:00补饲可使饲草干物质采食量更高（P = 0.04）（8.6千克/天对8.¹千克/天），而不限制放牧的母牛变化不大（07:00为8.2千克/天对18:00为8.4千克/天）。对于高草层高度的母牛，18:00补饲而非07:00补饲可使牧草干物质消化率更高（P = 0.03）（67.7%对64.5%），而低草层高度的母牛差异极小（18:00为65.4%对07:00为66.3%）。每天限制放牧12小时且07:00补饲而非18:00补饲的母牛可使可消化干物质采食量更高（P = 0.06）（5.0千克/天对4.7千克/天），而不限制放牧的母牛则表现出相反的反应（07:00可消化干物质采食量为4.6千克/天对18:00为4.9千克/天）。18:00补饲而非07:00补饲会使限制放牧的母牛比不限制放牧的母牛在更大程度上增加放牧时间（P = 0.09）。当饲草可利用性或放牧时间受到限制时（分别由于饲草供应量低和放牧机会受限），07:00补饲精料可提高饲草利用率和采食率，因为饲草干物质采食量、干物质消化率和可消化干物质采食量增加。然而，当饲草或放牧时间不受限时，18:00补饲精料可提高饲草利用率，因为牧草干物质消化率增加。
