Suppressed lymphocyte blastogenic responses and enhanced in vitro growth of infectious bovine rhinotracheitis virus in stressed feeder calves.

Hereford steers were stressed on a large-animal treadmill operating at speeds of 1.8 to 2.2 m/s. Blood samples were collected from indwelling jugular catheters before, during, and after exercise. Peripheral blood lymphocytes from stressed calves at 5 and 30 minutes after exercise had less (P less than 0.01) mitogen-induced blastogenic responses when compared to pre- or 60-minute postexercise values. Serum from stressed calves incorporated into lymphocyte cultures from nonstressed steers resulted in less (P less than 0.01) lymphocyte blastogenic responses. Infectious bovine rhinotracheitis viral growth in bovine kidney cell cultures was enhanced 4-fold when cultured with serum from stressed calves. These data indicate that acute physical exertion may cause physiologic alterations in calves that modulate cellular immunity and viral replication.