The effects of grazing management strategies on the vegetation, diet quality, intake and performance of free grazing sheep

Abstract

The typical steppe is a major region for sheep meat production in north of china, but most of the area has now become degraded inducing serious constraints for livestock management. In this study we compared the effects of the grazing management strategies on herbage mass (HM), sheep intake, diet chemical composition, and digestibility, and on live weight gain (LWG) of sheep grazing in typical steppe of north china during the growing season. Five grazing management strategies which have different stocking rate at different season were evaluated. The grazing managements were no grazing in the late spring and stocking rate at 9.3 and 6.7sheep/ha in the summer and autumn (SA1); no grazing in the late spring and stocking rate at 6.7 and 9.3sheep/ha in the summer and autumn (SA2); continuous grazing at 9.3sheep/ha through all seasons (SA3); continuous grazing at 9.3sheep/ha through late spring and summer and changing to 6.7sheep/ha in the autumn (SA4); continuous grazing at 6.7sheep/ha through all seasons (SA5). The results showed that HM decreased from 1.0tDM/ha at SA1 and SA2 to 0.34–0.37tDM/ha in SA3 and SA4 (P<0.05). Diet crude protein (CP) and DOM were higher in SA3 and SA4 compared to those in SA1, SA2 and SA5 (P<0.05). However, neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) contents in the diet and OMI per kg LW/d showed the opposite trends. DOM was positively related with CP (R=0.78, P<0.05) and negatively with NDF (R=–0.79, P<0.05), ADF (R=–0.69, P<0.05), and ADL (R=–0.67, P<0.05). OMI was only correlated with HM (R=0.39, P<0.05) and ADL (R=0.34, P<0.05). Both LWG per sheep and LWG per ha were decreased with the order: SA1, SA2, SA5, SA3 and SA4, which was remarkably related with stocking rate at the different grazing periods. The observations showed pronounced effects of grazing intensity and grazing period on animal and grassland productivity. The results suggested that deferred spring grazing combined with higher stocking rates in summer and relatively low stocking rates in autumn would be the best grazing strategy in this steppe. The study confirms the current central government's policy of defer spring grazing is benefit for the grassland productivity and ecological service. Therefore, the studies provide valuable evidence that farmers' practice of high stocking rate and grazing throughout the growing season are not sustainable for the grassland utilization.