T-cell deficiency in Suffolk lambs.

In a flock of Suffolk sheep respiratory diseases were regularly observed, while a flock of Booroola sheep kept under similar feeding and management conditions remained healthy. Experiments were conducted to compare the immunological and haematological parameters of Suffolk and Booroola sheep of different age groups. The percentage of T and B cells in the lymphocyte population and the capacity for blastogenesis induced by nonspecific mitogens were analyzed. Suffolk sucking lambs had significantly (P < 0.001) lower Concanavalin A (Con-A) induced blastogenesis and significantly lower T cell percentage at 6 months of age than Booroola lambs of the same age. B cell percentage and the rate of blastogenesis induced by Phaseolus vulgaris lectin (PHA) were lower in Suffolk lambs, though the differences were not significant. Sucking and growing Suffolk lambs had significantly (P < 0.01) lower red blood cell count and packed cell volume than Booroola lambs of the same age. Blood haemoglobin concentration was also lower in Suffolk lambs. No consistent differences were seen between the two breeds in total leucocyte count. T-cell deficiency and anaemia could be corrected by treatment with the immunomodulator levamisole (administered at a dose of 3 mg/kg body mass intramuscularly, twice with an interval of 10 days) and with vitamin B12 (1,000 micrograms/animal i.m.), respectively. On day 16 after the first treatment, the T-cell percentage, Con-A induced blastogenesis, red blood cell count, and packed cell volume of growing Suffolk lambs increased. T-cell deficiency and anaemia, either separately or together, may explain the lower resistance of Suffolk lambs to opportunistic pathogens. The relative contribution of genetic and environmental factors requires further studies.