Peripartum heat stress and supplementation with rumen-protected methionine: Effects on immune, metabolic, and inflammatory status of Holstein cows and their offspring.

This study investigated how supplementing a commercially available rumen-protected methionine (RPM) to heat-stressed Holstein cows during late gestation and early lactation affects immune, metabolic, and inflammatory biomarkers in the cows and their offspring exposed in utero. Fifty-three multiparous pregnant Holstein cows were housed in individual tiestalls and fed either a control dry-cow diet (CON, 2.2% Met of MP) or a CON diet supplemented with Smartamine M (Adisseo Inc.; MET, 2.6% Met of MP) and were maintained under thermoneutral conditions from wk -6 to -4 relative to parturition for acclimation. Four weeks before expected parturition, all MET cows and half of the CON cows were fitted with electric heat blankets (EHB) to induce heat stress (MET-EHB, n = 17; CON-EHB, n = 17). Cows fed CON diets without EHB served as thermoneutral controls (CON-TN, n = 19). Maternal treatments continued until 4 wk after parturition. Fifty-one calves exposed to the maternal treatments in utero for the last 4 wk of gestation were managed identically from birth to 180 d of age. Blood samples (cows: d 1, 8, 28 postpartum; calves: d 1, 7, 21, 35, 49 of age) and liver biopsies (cows: d 8, 28 postpartum; calves: d 1, 70 of age) were collected to assess immune and metabolic responses. In cows, EHB-induced heat stress reduced liver functionality index (LFI), increased IL-6 secretion following an ex vivo LPS challenge, and decreased hepatocyte counts while accumulating glutathione. Rumen-protected methionine tended to attenuate IL-6 and IL-1β responses and improved LFI and hepatic expression of Met-related genes. Heifers born to heat-stressed dams were lighter and displayed decreased cytokine responses, with maternal RPM primarily improving growth. Collectively, these findings show that periparturient heat stress impairs hepatic and immune function in the cow-calf pair, and RPM may partially mitigate these effects.