Effects of stocking rate on growth performance, energy and nitrogen utilization, methane emission, and grazing behavior in Tan sheep grazed on typical steppe

Understanding livestock performance in typical steppe ecosystems is essential for optimizing grassland-livestock interactions and minimizing environmental impact. To assess the effects of different stocking rates on the growth performance, energy and nitrogen utilization, methane (CH4) emissions, and grazing behavior of Tan sheep, a 2-year grazing experiment in the typical steppe was conducted. The grazing area was divided into 9 paddocks, each 0.5 ha, with 3 spatial replicates for each stocking rate treatment (4, 8, and 13 sheep per paddock), corresponding to 2.7, 5.3, and 8.7 sheep ha–1. The results showed that the neutral detergent fiber (NDF) and acid detergent fiber (ADF) contents of herbage varied between grazing years (P<0.05), with a positive correlation between stocking rate and crude fiber content in the herbage (P<0.05). Dry matter intake (DMI) decreased with increasing stocking rate (P<0.05), and the average daily gain (ADG) was highest at 2.7 sheep ha–1 (P<0.05). Compared to 2.7 and 8.7 sheep ha–1, the 5.3 sheep ha–1 treatment exhibited the lowest nutrient digestibility for dry matter, nitrogen, and ether extract (P<0.05). Fecal nitrogen was lowest at 8.7 sheep ha–1 (P<0.05), while retained nitrogen as a proportion of nitrogen intake was highest. Digestive energy (DE), metabolic energy (ME), and the ratios of DE to gross energy (GE) and ME to GE were highest at 8.7 sheep ha–1 (P<0.05). In contrast, CH4 emissions, CH4 per DMI, and CH4E as a proportion of GE were highest at 2.7 sheep ha–1 (P<0.05). Stocking rate and grazing year did not significantly affect rumen fermentation parameters, including volatile fatty acids, acetate, propionate, and the acetate/propionate ratio. At 8.7 sheep ha–1, daily grazing time and inter-individual distance increased, while time allocated to grazing, walking, and ruminating/resting decreased as stocking rates increased (P<0.05). This study highlights the importance of adjusting stocking rates based on the nutritional value of forage and grazing year to optimize grazing management.