Weaning management of newly received beef calves with or without continuous exposure to a persistently infected bovine viral diarrhea virus pen mate: Effects on rectal temperature and serum proinflammatory cytokine and haptoglobin concentrations.

Exposure to animals persistently infected (PI) with bovine viral diarrhea virus (BVDV) results in immunomodulation in cohorts. It is hypothesized that the extent of modulation differs for low-risk, precondi-tioned (PC) vs. high-risk, auction market (AM) beef cat-tle. Our objective was to compare immune responses of PC or AM calves in the presence (PI) or absence (CON) of a PI-BVDV pen mate. Crossbred PC steers (n = 27) from a single ranch origin were weaned, dewormed, vaccinated against respiratory and clostridial pathogens, tested for PI-BVDV, and kept on the ranch for 61 d. Subsequently, PC steers were transported to a receiv-ing unit (RU), weighed, stratified by d -1 BW, and assigned randomly to treatment (PCPI or PCCON) with no additional processing. Simultaneously, crossbred AM calves (n = 27) were assembled from regional auction markets and transported to the RU. The AM calves were weighed, stratified by gender and d -- 1 BW, processed under the same regimen used for PC steers at their origin ranch, except bull calves were castrated, then assigned randomly to treatment (AMPI or AMCON). Treatment pens were arranged spatially so that PI did not have fence line contact with CON. Blood samples were col-lected on d 0, 1, 3, 7, and 14 to determine serum con-centrations of haptoglobin (Hp), tumor necrosis factor-a (TNF-a), interferon-y (IFN-y), IL-4, and IL-6. Rectal temperature (RT) was recorded concurrent with blood sampling. In AM calves, RT and Hp increased (man-agement effect; P < 0.001) sharply on d 1; however, exposure to a PI-BVDV pen mate did not affect either variable (P > 0.79) during the 14-d evaluation period. Serum concentrations of TNF-a tended to increase (P = 0.09) for the PI cohort. A treatment x day interaction (P < 0.05) was observed for IFN-y on d 7 and 14 and IL-6 on d 14; these indices were greatest for AMPI. Results indicate weaning management and PI-BVDV exposure alter the immune status of newly received beef cattle. These main effects may be additive because proinflam-matory cytokine concentrations were greatest for AMPI. Therefore, results further indicate that potential health or growth consequences in cohorts exposed to a PI-BVDV pen mate are impacted by previous management and health history. [ABSTRACT FROM AUTHOR]