178 - Grazing Toxic Endophyte-infected Tall Fescue Alters Monocyte Abundance and White Blood Cell Expression of Prolactin and Nf-kb Pathway Genes in Beef Steers

The hypotheses tested were that (a) summer-long (84 d) grazing of endophyte-infected tall fescue (TE) would alter the count of circulating leukocytes (WBC) and WBC expression of key prolactin and NF-kB pathway genes and (b) that ad libitum intake of an 1:1 blend (MIX) sodium selenite (ISe) and SELPLEX vs ISe in a vitamin-mineral mix (V-M, 27 ppm Se) would ameliorate negative TE effects. Sixteen TE-naïve beef steers depleted of Se were randomly assigned to ad libitum consumption of ISe vs MIX for 35 d. Within Se-form treatments, 2 steers (ISe = 316±37 kg, MIX = 314±39 kg) were randomly assigned to graze each of 4, 2-acre TE paddocks for 84 d and had ad libitum access to their respective V-M. Paddock was the experimental unit (n = 4). The MIXED procedure of SAS was used to assess effect of grazing TE (d 0 vs 84), Se-form (ISe vs MIX), and their interaction on clinical parameters WBC, and relative mRNA content (RT-PCR) in blood. Whole blood Se was 24% greater (P < 0.01) for MIX steers and decreased (P < 0.01) 34% by d 84. Serum prolactin decreased 88% by d 84 and was 98% greater (P < 0.01) for MIX steers on d 84. Monocytes decreased (P < 0.01) 47% with TE and were 67% lower (P = 0.04) in MIX steers. Grazing of TE altered mRNA content of CISH, STA5B, PPIB, AGAP2, and SPRLR; and IL-8, RELA, NFKBIA, TLR, IKBKG, ZAP70, and LCK; of the prolactin (P ≤ 0.05) and NF-kB (P ≤ 0.04) pathways, respectively. In contrast, Se form had no effect (P ≥ 0.07) on mRNA content. Summer-long consumption of TE by steers altered monocyte numbers and expression of prolactin and NF-kB genes, but ad libitum intake of MIX Se forms did not ameliorate these effects.