Thymus-derived lymphocytes from weather-stressed calves decline in response t6 Concanavalin A (Con A) and Pokeweed Mitogen (PWM) as the age of calf increases. Maximal response is from 24-hr old normal calves; very little response is from Weak Calf Syndrome (WCS) calves. This depressed response reflects the observed thymus degeneration in WCS calves and contributes to the animals\u27 impaired immune system development