Effects of Supranutritional Selenium Supplementation During Different Trimesters of Pregnancy on Humoral Immunity in Beef Cattle at Parturition.

Supranutritional Se supplementation may improve immune responses in beef cattle. Immunity is compromised in beef cattle during the periparturient period. This study aims to determine the best time during pregnancy to supplement beef cows with Se-yeast to optimize humoral immunity at parturition. Multiparous, black Angus and Angus cross cows (n = 79) were used in the study. All cows had ad libitum access to a mineral supplement containing 120 mg/kg Se (US FDA regulations) from Na selenite. In addition, all cows except controls (CTR) received Se supplementation of 105 mg Se/week from Se-yeast boluses administered once weekly during their specific treatment trimester of gestation (TR1, TR2, or TR3) for 13 weeks. This dosage was supranutritional equaling 5 × the upper range of US FDA Se administration regulations. Blood was collected at parturition from all cows. Laboratory analyses studied to assess humoral immunity included measuring IBR, BVD types 1 and 2, PI3, and BRSV serum neutralization titers post vaccination, assessing total IgM and antigen-specific IgM concentrations, and determining complement-mediated bacterial killing percentages. Statistical analyses were performed using GraphPad Prism and SAS 9.4. Supranutritional Se-yeast supplementation increased whole-blood (WB) Se concentrations regardless of trimester of supplementation (all P < 0.0001). Supplementation during TR2 and TR3 was more effective in increasing WB-Se concentrations at parturition than during TR1 or CTR (all P < 0.0001). TR2 cows had higher serum neutralization titers for BRSV compared with CRT cows (P = 0.03). Total serum IgM and Vibrio coralliilyticus-specific IgM concentrations were highly correlated (r = 0.78; P < 0.0001). Compared with CTR cows, TR1, TR2, and TR3 cows had similar total IgM concentrations (all P ≥ 0.19) and similar Vibrio coralliilyticus-specific IgM concentrations (all P ≥ 0.47). Complement-mediated bacterial killing percentages were greater in TR2 and TR3 cows (> 99.6%) compared with TR1 (93.9%) and CTR (89.3%) cows, and all Se-supplemented TR groups were greater than CTR cows (all P ≤ 0.05). The significant group differences in the complement-mediated bacterial killing assay reflected WB-Se concentrations. Supranutritional Se-yeast supplementation during TR2 and TR3 is associated with higher serum neutralization titers for some viral antigens, as well as enhanced complement-mediated bacterial killing in cows at parturition. These findings suggest that Se supplementation during later trimesters of pregnancy may help combat infectious disease challenges during the periparturient period in beef cattle.