Lambs grazing with adult ewes prefer forbs with high-nutrient content in native grasslands dominated by Leymus chinensis and Stipa grandis

Authors: LI, PENGZHEN - China Agricultural University; ZHANG, ZHENHAO - China Agricultural University; Monaco, Thomas; ZHANG, HONGBO - China Agricultural University; RONG, YUPING - China Agricultural University

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2024
Publication Date: 11/18/2024
Citation: Li, P., Zhang, Z., Monaco, T.A., Zhang, H., Rong, Y. 2024. Lambs grazing with adult ewes prefer forbs with high-nutrient content in native grasslands dominated by Leymus chinensis and Stipa grandis. Ecology and Evolution. https://doi.org/10.1002/ece3.70609.
DOI: https://doi.org/10.1002/ece3.70609

Interpretive Summary: Dominant perennial grasses provide limited nutrition compared to forbs with higher crude protein (CP) content. In this study three sheep grazing strategies (lambs alone, mixed lambs and ewes, ewes alone) were used to explore diet selection. We investigated the influence of vegetation characteristic (aboveground biomass production, height, and species diversity) and foraging behavior (feed intake, organic matter digestibility, and daily grazing time) on dietary selection (taxonomic family richness and composition) for three months using DNA metabarcoding techniques. We also monitored daily grazing time and feed intake was estimated using an external marker (TiO2). Sheep primarily consumed Poaceae, Rosaceae and Cyperaceae families and both ewes and lambs in the mixed grazing strategy preferentially consumed forbs with diverse species composition, which contained higher CP than those available in the overall vegetation. Dietary richness was also strongly influenced by vegetation species diversity. Feed intake of lambs and ewes, however, were not different among the grazing strategies. Lambs in the lambs alone strategy had both greater daily grazing time and consumption of lower digestibility grass. Our study is the first to demonstrate that lambs can develop similar dietary selection and behavioral pattern when grazing with adult ewes in temperate grasslands. Our study indicates that conservation of vegetation species diversity in native grasslands is critical to livestock nutrition.

Technical Abstract: Grazing livestock in grasslands face the challenge of obtaining sufficient nutrition due to the uneven distribution of plant species and fluctuating vegetation productivity and nutrient levels. In northern China, Leymus chinensis and Stipa grandis are the dominate perennial species in native grasslands, but they provide limited nutrition compared to forbs with higher crude protein (CP) content. While dietary ingredients can affect the nutritional intake of grazing livestock, the influence of different grazing strategies on dietary selection remains unclear. In this study three sheep grazing strategies (lambs alone, mixed lambs and ewes, ewes alone) at the moderate stocking rate of 0.80 sheep ha-1year-1 were used to explore diet selection. We investigated the influence of vegetation characteristic (aboveground biomass production, height, and species diversity) and foraging behavior (feed intake, organic matter digestibility, and daily grazing time) on the mechanisms of dietary selection (taxonomic family richness and composition). Dietary selection was quantified for three months using DNA metabarcoding techniques through analyzing fecal samples. In addition, a triaxial accelerometer collar was placed on each sheep to monitor daily grazing time. Feed intake was estimated using an external marker (TiO2) and dietary organic matter digestibility was calculated from crude protein (CP) concentrations in the feces. Forage consumption across the grazing strategies revealed that species from Poaceae, Rosaceae and Cyperaceae families were frequently consumed. Both ewes and lambs in the mixed grazing strategy preferentially consumed forbs with diverse species composition (Jacob's D > 0), which contained higher CP than those available in the overall vegetation (p<0.05). In addition, dietary richness was significantly influenced by vegetation species diversity (p<0.05). Feed intake of lambs and ewes, however, were not significantly influenced by the different grazing strategies (p>0.05). Compared to lambs in the the mixed strategy, lambs in the lambs alone had both greater daily grazing time and consumption of lower digestibility grass (p < 0.05). Our study is the first to demonstrate that lambs can develop similar dietary selection and behavioral pattern when grazing with adult ewes in temperate grasslands. Our study indicates that conservation of vegetation species diversity in the native grasslands is critically beneficial to livestock nutrition.