Kersh Aaron J, Fraley Hannah M, Scasta J Derek, Derner Justin D, Lima Paulo de Mello Taveres, Stewart Whit C
Department of Animal Science, University of Wyoming, Laramie, WY, United States.
Department of Ecosystem Science and Management, University of Wyoming, Laramie, WY, United States.
Front Vet Sci. 2024 Nov 28;11:1502948. doi: 10.3389/fvets.2024.1502948. eCollection 2024.
Diet selection and composition of sheep target grazing plains larkspur ( Greene) in northern mixed-grass prairie were evaluated during a drought year (2022). Thirteen Rambouillet ewes (3-to 6-year-old, body weight (BW) 76 kg ± 2.9), 14 Dorper ewes (3-to 6-year-old, BW 47 kg ± 1.8), and 123 Dorper ram lambs (<1 year-old, BW 25 kg ± 0.4) were used for targeted grazing. Over the 20-day first phase (mid-May to early June), sheep were subjected to three stock density treatments: (1) high, 40 animal units (AU)/ha, (2) moderate, 20 AU/ha, and (3) light, 13 AU/ha. In the second phase (21 d, early-to late-June), the same sheep grazed four 1.5 ha paddocks sequentially at a very light stock density of 7 AU/ha. Dietary composition was assessed through focal bite count observations at the plant functional group level for phase one only, and dietary composition was estimated through fecal DNA metabarcoding (f.DNA) at the plant species level for both phases. Results indicated a uniformly low preference for larkspur (< 1% in diets). There were no significant effects of breed or age on focal bite count observations of plant functional groups (grasses, forbs, and larkspur), nor were there significant effects of breed or age on f.DNA diet proportions of plant functional groups ( > 0.05). Stock density did influence focal bite count observations, with higher forb intake ( = 0.0004) and lower grass intake ( = 0.009) observed at the moderate density compared to the high density. In phase two, grass and larkspur intake decreased while forb intake increased according to f.DNA ( < 0.01). These findings suggest that moderate stock density, combined with an understanding of plant phenology, precipitation variability, and animal forage preferences can optimize vegetation and animal performance in adaptive targeted grazing management within this ecosystem.
在干旱年份（2022年），对北部混合草草原上以草原翠雀（Greene）为目标的绵羊的饮食选择和组成进行了评估。选用了13只兰布耶母羊（3至6岁，体重（BW）76千克±2.9）、14只杜泊母羊（3至6岁，BW 47千克±1.8）和123只杜泊公羔羊（<1岁，BW 25千克±0.4）进行目标放牧。在20天的第一阶段（5月中旬至6月初），绵羊接受了三种载畜密度处理：（1）高，40个动物单位（AU）/公顷；（2）中，20 AU/公顷；（3）低，13 AU/公顷。在第二阶段（21天，6月上旬至下旬），相同的绵羊以7 AU/公顷的极低载畜密度依次在四个1.5公顷的围场放牧。仅在第一阶段通过对植物功能组水平的焦点咬食计数观察来评估饮食组成，两个阶段均通过粪便DNA宏条形码（f.DNA）在植物物种水平估计饮食组成。结果表明，对翠雀的偏好普遍较低（饮食中<1%）。品种或年龄对植物功能组（禾本科、杂类草和翠雀）的焦点咬食计数观察没有显著影响，品种或年龄对植物功能组的f.DNA饮食比例也没有显著影响（P>0.05）。载畜密度确实影响焦点咬食计数观察，与高密度相比，中等密度下观察到更高的杂类草摄入量（P = 0.0004）和更低的禾本科摄入量（P = 0.009）。在第二阶段，根据f.DNA，禾本科和翠雀的摄入量减少，而杂类草的摄入量增加（P<0.01）。这些发现表明，中等载畜密度，结合对植物物候、降水变异性和动物饲料偏好的了解，可以在该生态系统的适应性目标放牧管理中优化植被和动物性能。
