GROWTH, IMMUNE-RESPONSE, AND ESCHERICHIA-COLI RESISTANCE IN DWARF LINES OF CHICKEN AND THEIR CROSSES REARED UNDER DIFFERENT FEEDING REGIMENS

Growth, immune response, and disease resistance were measured in dwarf White Plymouth Rock chickens. Chicks from parental lines and reciproc al F-1 crosses between them were reared under three feeding regimens: (1) ad libitum (AL); (2) alternate-day (AD); and (3) alternate-day rel eased (ADR) where a sample of AD chicks was released to ad libitum fee ding at 28 days of age. Heterosis for body weight in AL increased init ially up to 14 days of age and declined thereafter in both males and f emales. Heterosis was consistently higher in males than females regard less of feeding regimen and also higher for AD and ADR than AL chicks. This suggested that heterosis for body weight was age- and environmen t-dependent. Among feeding regimens there were no differences in lesio n scores to E. coli challenge at 28 days of age while at 36 days lesio n scores were lower for AD than ADR and AL chicks. Antibody responses six days after inoculation with SRBC at 28 and 36 days of age mere low er for ADR than AL chicks suggesting that immunocompetence may be comp romised during periods of compensatory growth. Heterosis for resistanc e to E. call challenge and for antibody response was evident under all feeding regimens.