College of Grassland Science and Technology, China Agricultural University, Beijing 100193, China.
New South Wales Department of Primary Industries, Agricultural Research Institute, Orange, New South Wales 2800, Australia.
Animal. 2022 Jun;16(6):100546. doi: 10.1016/j.animal.2022.100546. Epub 2022 May 26.
Understanding the dynamic inter-relationship between grazing animals and the pasture sward is critical for sustainable grazing management. A field study was conducted to investigate the relationships between the quantity and quality characteristics of forages and diet selection of 30-kg Mongolian ewes in different seasons in Bromus inermis improved meadow steppe. Using a residual herbage mass method (1 000 kg/ha in spring, 800 kg/ha in summer and 600 kg/ha in autumn) to adjust stocking rate, three seasonal rest grazing strategies (spring rest, summer rest and autumn rest) combined with continuous grazing were studied. In each season, diet selection of sheep, quantified by diet composition and selectivity index, was estimated using a plant wax marker technique. Quantity (dry weight proportion, coverage, frequency, density and height) and quality (CP, NDF, ADF and DM digestibility) characteristics of forages consumed by sheep were determined simultaneously. Our results showed that in spring with the highest sward availability (herbage mass), diet selection of sheep could be predicted by the positive linear relationship between quality characteristics of forages and their selectivity index. In summer, the diet selection could be predicted by both positive linear relationship between quality characteristics and selectivity index, and the relationship between quantity characteristics and diet composition. While in autumn with the lowest sward availability, it could be predicted by the positive linear relationship between quantity characteristics and diet composition. During the whole grazing season, the diet composition of B. inermis (40.4%) and Leymus chinensis (35.1%) were larger than that of Potentilla bifurca (9.5%) and Carex (15.1%) and the selectivity index of P. bifurca was the highest (0.62), followed by Carex (0.17) and B. inermis (0.05), and L. chinensis (-0.29) was the lowest. The two parameters of diet selection above were positively related to their quantity and quality characteristics, respectively. These results suggested that the influence of quality characteristics on diet selection of sheep decreased gradually as a result of the decline in sward availability, while the influence of quantity characteristics increased. This study provides a comprehensive understanding of diet selection of sheep examining the trade-offs between quantity and quality characteristics of forages. The knowledge of diet selection of sheep and the corresponding prediction regressions acquired in this study could give the basis for designing appropriate grazing management strategies.
了解放牧动物与草地草丛之间的动态相互关系对于可持续放牧管理至关重要。本研究在贝加尔针茅草改良羊草草地进行了一项野外试验，以 30 公斤蒙古母羊为研究对象，在不同季节采用剩余牧草质量法（春季 1000 公斤/公顷、夏季 800 公斤/公顷和秋季 600 公斤/公顷）调整载畜率，研究了三种季节性休牧策略（春季休牧、夏季休牧和秋季休牧）与连续放牧相结合的情况。在每个季节，采用植物蜡示踪技术估算绵羊的饮食选择，通过饮食组成和选择性指数来量化。同时，确定绵羊所消耗牧草的数量（干重比例、盖度、频率、密度和高度）和质量（CP、NDF、ADF 和 DM 消化率）特征。结果表明，春季草地可利用性（牧草量）最高，绵羊的饮食选择可通过牧草质量特征与其选择性指数之间的正线性关系来预测。在夏季，饮食选择可通过牧草质量特征与选择性指数之间的正线性关系以及数量特征与饮食组成之间的关系来预测。而在秋季草地可利用性最低的情况下，可通过数量特征与饮食组成之间的正线性关系来预测。在整个放牧季节，羊草（40.4%）和中华羊茅（35.1%）的饮食组成大于扁蓄（9.5%）和薹草（15.1%），扁蓄的选择性指数最高（0.62），其次是薹草（0.17）和羊草（0.05），中华羊茅的选择性指数最低（-0.29）。饮食选择的这两个参数分别与它们的数量和质量特征呈正相关。这些结果表明，随着草地可利用性的下降，质量特征对绵羊饮食选择的影响逐渐减弱，而数量特征的影响增加。本研究全面了解了绵羊的饮食选择，考察了牧草数量和质量特征之间的权衡关系。本研究中获得的绵羊饮食选择知识和相应的预测回归可以为设计适当的放牧管理策略提供依据。
