Effects of beta-adrenergic receptor agonist and low environmental temperature on the immune system of growing lambs

Sixteen lambs were studied to examine the effects of cold environment and a beta-agonist on their immune status. The beta-agonist, L-646, 969, was fed for 4 wk at 0.28 or O mg kg ^-0.75BW to animals housed in a warm (20°C) or a moderately cold (O°C) environment. The cold environment suppressed PWM-stimulated proliferation at week 3 (P < 0.03) and week 4 (P < 0.01 ). The percentage of CD4 cells and CD4:CD8 cell ratio were decreased at week 1 (P < 0.02; P < 0.05) and week 3 (P < 0.001; P < 0.003), and the percentage of CD2 cells (P < 0.05) was decreased at week 2 at the low-temperature. The beta-agonist did not influence leukocyte profile and lymphocyte functions. The results suggest that a cold environment may influence immune function by suppressing lymphocytes expressing CD2, CD4 and CD4:CD8 cell ratio, and changing lymphocyte proliferative response to a T cell mitogen. Further investigation is required to identify the effects of prolonged and intense cold exposure on the immune system with a large number of animals and the implications of current observations for the health of animals in a cold environment.