GROWTH, IMMUNORESPONSIVENESS, AND DISEASE RESISTANCE OF DIVERSE STOCKS OF CHICKENS REARED UNDER 2 NUTRITIONAL REGIMENS

Growth, immunocompetence, and disease resistance were measured in a co mmercial broiler stock (BC), a commercial white-egg-layer stock (LC), and a White Plymouth Rock line selected for high juvenile BW (HW) unde r dietary regimes differing in protein and energy content. Diet E had 20% more protein and 17% more ME than Diet A. Stock by sex interaction s were significant for BW at 28 and 36 d of age because sexual dimorph ism occurred at younger ages in the meat than in the layer stocks. Whe n inoculated with .1 mt of a .25 or 2.50% suspension of SRBC, diet by stock interactions were significant for antibody titers 6 d postinocul ation (PI) at the lower dosage. Interactions were not present at the h igher dosage or for either dosage 13 d PI. Diet by stock interactions were significant at both dosages for change in SRBC titers from 6 to 1 3 d PI. The interactions resulted from a significantly smaller decline in BC than HW or LC chicks fed Diet A, whereas all stocks responded s imilarly when fed Diet E. A significant decline in rate of BW gain was observed in chicks inoculated with marble spleen disease virus (MSDV) , with the increase in relative weight of spleen significantly greater for LC than HW or BC chicks 6 d PI. When heterophil to lymphocyte rat ios were used as an assay of response to MSDV challenge, ratios were s ignificantly higher for HW chicks fed Diet A than for chicks fed Diet E and for LC chicks fed Diet E than for chicks fed Diet A, but not dif ferent for BC chicks on the two diets.