Department of Animal Science, University of Arkansas Division of Agriculture, Fayetteville 72701, USA.
J Anim Sci. 2009 Nov;87(11):3817-24. doi: 10.2527/jas.2009-2094. Epub 2009 Aug 14.
The objective of the present experiment was to describe the sward canopy structures of 3 different wheat (Triticum aestivum L.) pastures and relate them to short-term herbage intake rate and foraging dynamics by steers. Pastures were sampled for leaf and stem fractions at the bottom, middle, and top canopy strata. Sward surface heights and tiller and bulk densities were measured. Herbage was separated into stem and leaf, and leaves were then ranked phenologically. Three steers grazed (grazing sessions) 3 different pastures in a Latin square design. Ruminal contents were emptied and weighed before and after grazing sessions to assess herbage intake rate and bite mass. All grazing sessions were video recorded and analyzed for feeding stations (eating steps demarking the potential area of herbage consumption), bites per feeding station, and feeding stations per minute. Bite depth, bite area, and area grazed per feeding station were calculated. Morphological components and tiller density did not differ (P > 0.05) between the pastures, but sward surface height (P < 0.05) and leaf proportions in the middle and top canopy strata did differ. The herbage intake rate, bite mass, and bite area differed between treatments (P < 0.05). Steers grazing the tallest pasture with the greatest leaf accessibility ate faster, navigated slower, and grazed more efficiently (P < 0.05). The area grazed per feeding station differed between treatments (P < 0.05), being 87% for the tallest pasture with the greatest leaf accessibility and the least, 31%, for the pasture with the least leaf accessibility. Pastures with greater leaf accessibility may lead grazing cattle to reach the same herbage intake amount in less time while grazing more efficiently per unit area. Therefore, it may be logical to reduce the area and time allocations in pastures with taller swards where a leafy upper canopy stratum is found.
本实验的目的是描述 3 种不同小麦（Triticum aestivum L.）草地的草丛冠层结构，并将其与短期牧草采食量和牛的采食动态联系起来。在底层、中层和顶层冠层采集叶片和茎秆部分的样方。测量草丛表面高度、分蘖和总体密度。将牧草分为茎和叶，然后按叶龄分级。三头牛在拉丁方设计中分别放牧（放牧期）3 种不同的草地。放牧前后排空并称重瘤胃内容物，以评估牧草采食量和咬质量。所有放牧期均进行视频记录和分析，以确定采食站（标记潜在牧草采食区的采食步）、每个采食站的采食次数和每分钟的采食站数。计算采食深度、采食面积和每个采食站的采食面积。不同草地间形态组分和分蘖密度没有差异（P＞0.05），但草丛表面高度（P＜0.05）和中层及顶层冠层叶片比例有差异。牧草采食量、咬质量和采食面积因处理而异（P＜0.05）。放牧最高、叶片最易接近草地的牛采食速度更快、移动速度更慢、采食效率更高（P＜0.05）。每个采食站的采食面积因处理而异（P＜0.05），叶片最易接近、最高的草地为 87%，叶片最不易接近的草地为 31%。叶片更易接近的草地可能使放牧牛在更短的时间内达到相同的牧草采食量，同时单位面积的采食效率更高。因此，在发现上层叶片茂密的高草丛草地中，减少草地面积和时间分配可能是合理的。
