Northern Ag Research Center, Montana State University, Havre, Montana, United States of America.
Department of Animal and Range Sciences, Montana State University, Bozeman, Montana, United States of America.
PLoS One. 2020 Oct 13;15(10):e0240629. doi: 10.1371/journal.pone.0240629. eCollection 2020.
Dormant season livestock grazing reduces reliance on harvested feeds, but typically requires protein supplementation to maintain animal performance. Individual variation in supplement intake can impact animal performance; however, it is unknown if this variation leads to individual or herd-level effects on grazing behavior, resource utilization, and grazing impacts to native rangelands. To examine effects of protein supplementation on dormant season cattle resource use and, subsequently, post-grazing habitat conditions, we examined cattle grazing behavior, resource utilization and biomass removal of vegetation on a native rangeland in Montana. A commercial herd of 272 (yr 1) and 302 (yr 2) cows grazed a 329-ha rangeland pasture from November to January. Intake of a 30% crude protein supplement was measured for each individual. Five individuals within each of six age groups were equipped with GPS collars. Time spent grazing declined with supplement intake ([Formula: see text] = -0.05 ± 0.02; P < 0.01). Distance traveled per day had a positive asymptotic association with supplement intake ([Formula: see text] = 0.35 ± 0.09; P < 0.01). On average, resource utilization by cattle grazing dormant season forage decreased with terrain ruggedness ([Formula: see text] = -0.09 ± 0.03), but was unrelated to aspect, temperature and wind speed. Notably, we observed high individual variability in resource utilization for elevation, distance from supplement and water. A post-hoc analysis suggested that individual attributes (age, body weight, supplement intake) influenced cattle resource use. At moderate stocking rates, dormant season livestock grazing did not affect residual vegetation conditions (P values > 0.22). However, residual cover of forbs and litter increased with relative grazing intensity ([Formula: see text] = 1.04 ± 0.41; [Formula: see text] = 3.06 ± 0.89; P ≤ 0.05). In summary, high individual variability in grazing resource utilization of cattle suggests individual-level factors could be the dominant drivers in grazing behavior and landscape use.
休眠季节牲畜放牧减少了对收获饲料的依赖，但通常需要蛋白质补充来维持动物性能。补充剂摄入量的个体差异会影响动物性能；然而，尚不清楚这种差异是否会对放牧行为、资源利用以及对原生牧场的放牧影响产生个体或群体影响。为了研究蛋白质补充对休眠季节牛资源利用的影响，以及随后对放牧后栖息地条件的影响，我们检查了蒙大拿州原生牧场牛的放牧行为、资源利用和植被生物量去除情况。一个由 272 头（第 1 年）和 302 头（第 2 年）母牛组成的商业牛群从 11 月到 1 月在一个 329 公顷的牧场放牧。对每个个体的 30%粗蛋白补充剂摄入量进行了测量。在六个年龄组中的每个年龄组中，有五头个体配备了 GPS 项圈。随着补充剂摄入量的增加，牛的放牧时间减少（[公式：见文本] = -0.05 ± 0.02；P < 0.01）。每天行进的距离与补充剂摄入量呈正渐近关系（[公式：见文本] = 0.35 ± 0.09；P < 0.01）。平均而言，牛在休眠季节放牧时对牧草的资源利用随着地形崎岖度的增加而减少（[公式：见文本] = -0.09 ± 0.03），但与方位、温度和风速无关。值得注意的是，我们观察到牛在海拔、离补充剂和水的距离等资源利用方面存在高度的个体变异性。事后分析表明，个体属性（年龄、体重、补充剂摄入量）影响牛的资源利用。在中等放牧率下，休眠季节牲畜放牧不会影响剩余植被条件（P 值> 0.22）。然而，随着相对放牧强度的增加，杂草和枯枝落叶的残留覆盖增加（[公式：见文本] = 1.04 ± 0.41；[公式：见文本] = 3.06 ± 0.89；P ≤ 0.05）。总之，牛对放牧资源利用的个体差异很大，这表明个体水平因素可能是放牧行为和景观利用的主要驱动因素。
