Effects of stocking rate on grazing behavior, nitrogen and energy metabolism, and greenhouse gas emissions of Simmental cattle in saline meadow.

A rational stocking rate balances grassland ecosystems and improves livestock productivity. This study examined how stocking rates affect Simmental cattle in saline meadow through analyses of grazing behavior, nitrogen (N) and energy metabolism, and greenhouse gas emissions, to inform targeted livestock management. A total of 24 male Simmental cattle (3-month-old, 104.72 ± 1.78 kg) were selected and assigned to stocking rates of 0.66, 1.33, and 2.66 cattle/ha (8 cattle/treatment). The experiment adopted a rotational grazing system, with three paddocks as replicates for each stocking rate, and lasted for 90 d. Each paddock was grazed for 10 d and rested for 20 d. The rumination rate (P = 0.002), chews per bolus (P = 0.017), and average daily gain (P < 0.001) were lower in the 2.66 cattle/ha than in the 0.66 and 1.33 cattle/ha. The stocking rate of 1.33 cattle/ha increased (P < 0.001) crude protein digestibility, retention N, retention energy, N and energy utilization, decreased urinary energy (P = 0.012), CO2 emission and intensity (P < 0.001), CH4 energy/digestible energy (P = 0.001), and CH4 energy/metabolizable energy (P = 0.001), and resulted in the lowest CH4 energy output. At this stocking rate, the CO2 or CH4 intensities increased by 0.390 or 0.018 g/kg metabolic body weight (BW0.75) per d, respectively, with an increase of 1 g/kg BW0.75 per d of dry matter intake (P < 0.001). The metabolizable energy requirement for maintenance (MEm) was 0.98% and 2.40% lower (P < 0.001), while the metabolizable energy maintenance utilization efficiency (Km) was 1.08% and 0.96% higher for 1.33 cattle/ha compared to 0.66 and 2.66 cattle/ha, respectively. Therefore, a stocking rate of 1.33 cattle/ha is optimal for saline meadow in arid regions, as it increases utilization of N or energy and Km, while decreases CO2 emissions and CH4 energy losses.