Effects of forage composition on metabolism of nutrients and minerals in sheep under different degradation stages of Songnen grassland simulated by house feeding

In this study, sheep were used as test animals to study the effects of forage composition at different degradation stages on nutrient and mineral metabolism of sheep through digestion and metabolism experiments, so as to provide reference for evaluating the effects of grassland degradation on nutrient intake and nutritional supplement of grazing sheep. Twelve（30.49±4.31 kg BW）German Merino crossbred sheep were randomly divided into three treatment groups with four replicates in each treatment and one sheep in each replicate. Forage at different degradation stages was used as the source of total diet in each group, respectively. In undegraded grassland, moderately degraded grassland and severely degraded grassland, the trial feeding experiment lasted for 60 days, and the digestion and metabolism experiment lasted for 4 days. The results showed that compared with the undegraded grassland, the digestibilities of DM, CP and NDF of sheep were significantly increased in severely degraded grassland（P＜0.01）, and significantly increased the digestibilities of OM in sheep（P＜0.05）. Compared with undegraded grassland, moderate degraded grassland and severely degraded grassland significantly increased the protein intake of sheep（P＜0.05）. With the deepening of undegraded degradation, the intake of sodium, magnesium, iron, copper and manganese of sheep increased significantly（P＜0.01）. Compared with the mineral requirements of sheep recommended by NRC, the forage composition diets at different degradation stages could meet the needs of calcium,phosphorus, sodium, potassium, magnesium, sulfur, manganese and iron, but could not meet the needs of zinc and copper. From the perspective of absorption and utilization, undegraded grassland could not meet the requirement of sheep sulfur. Undegraded grasslands and moderately degraded grasslands could not meet the needs of sheep iron.