Supplementation with rumen-protected methionine or choline during the transition period influences whole-blood immune response in periparturient dairy cows.

Methionine, together with Lys, is the most limiting AA for milk production in dairy cows. Besides its crucial role in milk production, Met and its derivate metabolites (e.g., glutathione, taurine, polyamines) are well-known immunonutrients in nonruminants, helping support and boost immune function and activity. In the present study, the effects of Met or choline, as its precursor, were investigated using an ex vivo whole blood challenge. The study involved 33 multiparous Holstein cows (from a larger cohort with a factorial arrangement of treatments) assigned from d -21 to +30 relative to parturition to a basal control (CON) diet, CON plus rumen-protected Met (MET, Smartamine M, Adisseo NA, Alpharetta, GA) at a rate of 0.08% of dry matter, or CON plus rumen-protected choline (CHOL, ReaShure, Balchem Inc., New Hampton, NY) at 60 g/d. Blood was sampled on d -15, -7, 2, 7, and 20 for ex vivo lipopolysaccharide (LPS) challenge, and on d 1, 4, 14, and 28 relative to parturition for phagocytosis and oxidative burst assays. The MET cows had greater energy-corrected milk production and milk protein content. Overall, IL-6 response to LPS increased around parturition, whereas IL-1β remained constant, casting doubt on the existence of systemic immunosuppression in the peripartal period. Supplementation with MET dampened the postpartal blood response to LPS (lower IL-1β), while improving postpartum neutrophil and monocyte phagocytosis capacity and oxidative burst activity. In contrast, CHOL supplementation increased monocyte phagocytosis capacity. Overall, the data revealed a peripartal immune hyper-response, which appeared to have been mitigated by MET supplementation. Both MET and CHOL effectively improved immune function; however, MET affected the immune and antioxidant status before parturition, which might have been beneficial to prepare the cow to respond to metabolic challenges after parturition. These results provide insights on potential differences in the immunomodulatory action of methionine and choline in dairy cows. As such, the effects observed could have implications for ration formulation and dietary strategies.