Department of Animal Science, Iowa State University, Ames 50011, Iowa, USA.
J Anim Sci. 2011 Oct;89(10):3236-47. doi: 10.2527/jas.2010-3594. Epub 2011 Apr 29.
A 2-yr grazing experiment was conducted to assess the effects of grazing management on cattle distribution and pasture and stream bank characteristics. Six 12.1-ha cool-season grass pastures in central Iowa were allotted to 1 of 3 treatments: continuous stocking with unrestricted stream access (CSU), continuous stocking with stream access restricted to 4.9-m-wide stabilized crossings (CSR), or rotational stocking with stream access restricted to a riparian paddock (RP). Pastures were stocked with 15 fall-calving Angus cows (Bos taurus L.) from mid-May to mid-October for 153 d in 2008 and 2009. A global positioning system (GPS) collar recording cow position every 10 min was placed on at least 1 cow per pasture for 2 wk of each month from May through September. Off-stream water was provided to cattle in CSU and CSR treatments during the second of the 2 wk when GPS collars were on the cattle. A black globe temperature relative humidity index (BGTHI) was measured at 10-min intervals to match the time of the GPS measurements. Each month of the grazing season, forage characteristics (sward height, forage mass, and CP, IVDMD, and P concentrations) and bare and fecal-covered ground were measured. Stream bank erosion susceptibility was visually scored in May, August, and October (pre-, mid-, and post-stocking). Cattle in RP and CSR treatments spent less time (P < 0.10) within the stream zone (0 to 3 m from stream center) in June and August and in the streamside zone (0 to 33 m from stream zone) in May through August and May through September, respectively, than cattle in CSU pastures. However, off-stream water had no effect on cattle distribution. Compared with the CSU treatment, the CSR treatment reduced the probability (P < 0.10) that cattle were within the riparian zone (0 to 36 m from stream center) at BGTHI of 50 to 100. Bare ground was greater (P < 0.10) in pastures with the CSU than CSR and RP treatments in the stream and streamside zones in September and October and in July and September. Streams in pastures with the CSU treatment had less stable banks (P < 0.10) mid- and post-stocking than RP or CSR treatments. Results show that time spent by cattle near pasture streams can be reduced by RP or CSR treatments, thereby decreasing risks of sediment and nutrient loading of pasture streams even during periods of increased BGTHI.
一项为期两年的放牧实验旨在评估放牧管理对牛群分布以及牧场和溪流岸特征的影响。在爱荷华州中部，将 6 个 12.1 公顷的冷季草地牧场分配到 3 种处理方式之一：无限制进入溪流的连续放牧（CSU）、限制进入溪流宽度为 4.9 米的稳定交叉口的连续放牧（CSR）或限制进入河岸围场的轮牧（RP）。在 2008 年和 2009 年的 153 天中，从 5 月中旬到 10 月中旬，每个牧场至少有 15 头秋季产犊的安格斯牛（Bos taurus L.）被放牧，持续放牧 153 天。在 GPS 项圈放在牛身上的每个月的 5 月至 9 月的 2 周中的第 2 周，为 CSU 和 CSR 处理中的牛提供了离溪水源。在 GPS 测量的同时，每 10 分钟记录一次牛的位置的全球定位系统（GPS）项圈。在放牧季节的每个月，测量草料特性（草丛高度、草料量、CP、IVDMD 和 P 浓度）、裸露和粪便覆盖地面。在 5 月、8 月和 10 月（放牧前、中、后期），对溪流岸侵蚀易感性进行了目视评分。在 6 月和 8 月，以及在 5 月至 8 月和 5 月至 9 月，RP 和 CSR 处理中的牛在溪流区（溪流中心 0 至 3 米）和溪流岸区（溪流区 0 至 33 米）内的时间（P < 0.10）少于 CSU 牧场中的牛。然而，离溪水源并没有影响牛的分布。与 CSU 处理相比，CSR 处理降低了牛在 BGTHI 为 50 至 100 时处于河岸带（从溪流中心 0 至 36 米）的概率（P < 0.10）。在 9 月和 10 月以及 7 月和 9 月，CSU 处理的牧场中，溪流区和溪流岸区的裸地（P < 0.10）大于 CSR 和 RP 处理的牧场。在放牧后的中期和后期，CSU 处理的溪流中，与 RP 或 CSR 处理相比，其河岸更不稳定（P < 0.10）。结果表明，通过 RP 或 CSR 处理可以减少牛群在牧场溪流附近的时间，从而即使在 BGTHI 增加的时期，也可以降低牧场溪流的泥沙和养分负荷风险。
