Environment and Management I

prolonged incubation. HuO lytic titers were typically lower than those for Rb in the same sera.In 91 commercial drakes complete HuO lysis occurred in 14/91 (15%), ≥ 50% lysis in 51/91 (56%), but 7 (8%) sera were negative. Heating sera reduced lytic capacity for both HuO and Rb but not to the same degree. Nearly all HuO lytic capacity was removed after 10 min exposure to 57°C while the same treatment reduced Rb lytic capacity by only 50%.Chelation of Ca++ by EGTA interfered with Rb lysis suggesting inhibition of the classic complement pathway (CP) perhaps by interference at the C1 q-r-s levels. EGTA had little inhibitory effect on HuO lysis, supporting an alternate pathway (AP) mechanism. EGTA did not affect Rb agglutination. The addition of carbohydrates, especially melibiose and galactose, to diluents reduces both agglutination and lysis of Rb but has little effect on HuO lysis. This supports a role for anti-Gal as the antibody providing the substrate for CP lysis of Rb and tends rule out an antibody requirement for HuO lysis. Collectively these 2 systems seem to provide a convenient means for investigating innate and acquired immunity of ducks. Moreover the heterogeneity in lytic capacity for HuO of market age ducks may offer a screening tool for identifying those with a weak immunity.