Dietary copper levels affect mineral absorbability, rumen microbial composition and metabolites of the grazing Mongolian sheep

Copper (Cu) is a critical limiting factor in grazing livestock production in Inner Mongolia. This study investigated the effects of Cu-deficient and Cu-supplemented diets on production metrics, nutrient digestion and absorption, ruminal microbiota, and metabolites in grazing Mongolian sheep. A total of 28 individually-housed Mongolian sheep were randomly assigned to a Cu-deficient feeding group (LCu) and a Cu-deficient feeding control group (LCG), supplemented with a multi-nutrient salt containing 0 mg Cu and 14.3 mg Cu, respectively, for 53 continuous days. Following this, a 7-day digestion test was conducted, after which seven sheep from each group were randomly slaughtered. The remaining sheep in LCu and LCG transitioned to a Cu-supplemented feeding group (SCu) and a Cu-supplemented feeding control group (SCG), receiving multi-nutrient salts with 43.0 mg Cu and 14.3 mg Cu, respectively. This phase entailed a 34-day diet acclimatization period, a 7-day digestion test, and eventual slaughter. The LCu diet significantly decreased the ruminal Cu and sulfur (S) content, as well as Cu apparent absorbability, compared to the LCG group (P<0.05). Conversely, SCu significantly increased the ruminal Cu content and the apparent absorbability of phosphorus (P), S, potassium (K), calcium (Ca), manganese (Mn), iron (Fe), Cu and zinc (Zn) compared to the SCG group (P<0.05). Amplicon sequencing analysis revealed a significant downregulation of Alistipes and Barnesiella (P<0.05) in the LCu group. Metabolomic analyses supported an elevation in ruminal citrulline and L-ornithine levels, affecting amino acid metabolic pathways in the LCu group (P<0.05). In the SCu group, there was a significant increase in the relative abundance of Saccharofermentans and Ruminococcus (P<0.05), with metabolomic analysis revealed elevated levels of nucleic acid and purine analog affecting purine metabolic pathways (P<0.05). Notably, neither treatment had a significant impact production metrics, rumen fermentation parameters, or the apparent digestibility of crude protein, acid detergent fiber and neutral detergent fiber (P>0.05). In conclusion, a Cu-deficient diet impairs Cu absorption and nutrient catabolism in grazing Mongolian sheep, while Cu supplementation effectively alleviated these deficiencies and enhances the absorption of various minerals.