Mixed grazing of lambs and ewes improves lamb growth performance by reducing foraging time and activity-related...

Temperate grasslands exhibit spatial and temporal heterogeneity in terms of plant species composition, vegetation productivity, and forage nutrition. These characteristics can influence the animal behavior and performance of livestock. Combinations of different livestock species such as cattle and sheep have shown benefits on vegetation productivity and animal performance, while mixture grazing with lambs and ewes on sheep grazing behavior and growth performance remain unclear. We conducted a grazing experiment using randomized block design with three replicates at a temperate grassland in northern China. In this study, three sheep grazing strategies (LA = lambs grazing alone; LM/EM = mixture grazing of lambs and ewes; EA = ewes grazing alone) were studied at a stocking rate of 0.89 sheep·ha^-1·year^-1 from June to September in 2022 and 2023. Differences in vegetation characteristics, grazing behavior, and sheep growth performance were analyzed using t-test and two-way ANOVA. Subsequently, structural equation modeling (SEM) was applied to explore the relationships among these variables under different grazing strategies and their effects on sheep growth performance. Above-ground biomass (AGB) of vegetation under LM/EM (140.27 ± 7.02 g m^-2) was higher than that of EA (101.58 ± 2.53 g m^-2; P < 0.05). AGB, plant species richness, and crude protein concentration all showed a gradually decreasing trend with the extension of grazing time. Lambs had a daily foraging time of 9.19 ± 0.14 h and an energy expenditure of 399.65 ± 8.24 kJ kg^-1·BW^-0.75·day^-1 under LA, both significantly higher than those of lambs under LM/EM (8.52 ± 0.21 h·day^-1 and 366.65 ± 10.09 kJ kg^-1·BW^-0.75·day^-1; P < 0.05). However, their organic matter digestibility (56.80 % ± 1.35) was significantly lower than that of mixed grazing lambs (61 % ± 0.75). Average daily liveweight gain (ADG) per hectare followed the sequence of LA, LM/EM and EA, while ADG per animal showed no significant difference between LM/EM and LA. This key difference among grazing strategies was mainly due to greater crude protein intake and lower grazing energy expenditure under mixed grazing, which together enhanced lamb growth performance. These findings demonstrate that mixed grazing is an effective strategy to enhance pasture productivity, improve animal performance, and promote sustainable grassland management.