Dietary selenium levels affect mineral absorbability, rumen fermentation, microbial composition and metabolites of the grazing sheep

Abstract

Selenium (Se) is an essential trace element for the growth of all livestock. However, little is known about the effects of dietary selenium levels on production metrics, nutrient digestion and absorption, ruminal microbiota, and metabolites in grazing sheep. Therefore, in this research, 28 individually-housed grazing sheep were randomly divided into a low-Se feeding group (LSe) and a control group for the low-Se feeding phase (LCG), supplemented with multi-nutrient salts containing 0 mg Se and 0.63 mg Se, respectively, for 53 days. After 53 days of feeding, a 7-day digestion test was conducted, then seven sheep in each group were randomly slaughtered. Then, the remaining sheep in LSe and LCG were transferred to a high-Se supplementation group (SSe) and a control group for the high-Se feeding phase (SCG), supplemented with multi-nutrient salts containing 1.90 mg and 0.63 mg Se, respectively. This phase consisted of a 34-day diet adaptation period, a 7-day digestive test, and eventual slaughter. LSe reduced and elevated ruminal Se and copper (Cu) content, respectively, and decreased Se apparent absorbability compared to LCG (P < 0.05). Conversely, SSe reduced and increased ruminal Cu and Se content, respectively, and increased Se apparent absorption in comparison to SCG (P < 0.05). It also increased the ruminal NH3-N concentration (P < 0.05). Amplicon sequencing analysis revealed a decrease in Lentimicrobium and Treponema abundance and an increase in Lawsonibacter and Sporobacter abundance (P < 0.05) in LSe group. Metabolomic analysis confirmed an elevated level of ruminal citrulline, ornithine and glutathione affecting amino acid and glutathione metabolic pathways (P < 0.05) in LSe group. In SSe group, Alistipes were significantly reduced (P < 0.05) with metabolomics showing elevated levels of L-carnitine and arginine, affecting ruminal antioxidant capacity and arginine biosynthesis pathways (P < 0.05). Notably, both treatments had no significant effect on production metrics and apparent digestibility of organic nutrients (P > 0.05). In conclusion, Se deficiency affects Se absorption and amino acid metabolism in grazing sheep, while supplementing Se in diet effectively ameliorates these deficiencies and improves ruminal antioxidant capacity.