The effects of dietary supplementation with rumen‐protected amino acids on the expression of several genes involved in the immune system of dairy sheep

Amino acids might be a tool to transform animals from a pro‐ to an anti‐inflammatory phenotype through the downregulation of several genes (TLR‐4, NF‐κB, TNFa, IL‐1β, IL‐2, IL‐6, IL‐8, CCL‐5 and CXCL‐16) whose expression increases during inflammation. To examine this possibility, each of sixty Chios dairy sheep was assigned to one of the following five dietary treatments: A: basal diet (control group); B: basal diet +6.0 g/head rumen‐protected methionine (MetaSmart™); C: basal diet +5.0 g/head rumen‐protected lysine (LysiGEM™); D: basal diet +6.0 g/head MetaSmart™ + 5.0 g/head LysiGEM™; and E: basal diet +12.0 g/head MetaSmart™ + 5.0 g/head LysiGEM. The results showed a significant downregulation in the expression of the TLR‐4 gene in both the macrophages and the neutrophils of ewes fed rumen‐protected amino acids. Significantly lower mRNA transcript accumulation was also observed for the TNFa, IL‐1β and CXCL‐16 genes in the macrophages and for the IL‐1β gene in the neutrophils of ewes supplemented with amino acids. The ewes that received dietary supplementation with rumen‐protected lysine alone (C) had significantly lower CCL‐5 transcript levels in their macrophages than the ewes fed the other supplemented diets. Diet D enhanced the mRNA expression of the IL‐2 gene in ewe neutrophils. Negative correlations were found between: a. TLR‐4, TNFa, IL‐1β and CXCL‐16 gene expression in macrophages and the milk fat and total solids content; b. CCL‐5 gene expression in neutrophils and the milk yield and FCM₍₆%₎; and c. CXCL‐16 gene expression and the milk protein content. Moreover, positive correlations were found between the BHBA concentration and the expression of the TLR‐4 and CXCL‐16 genes in macrophages. In conclusion, the rumen‐protected amino acids improved sheep metabolism (as indicated by reduced blood BHBA and urea concentrations), milk chemical composition and immune system function.