Previous phenotypic selection on residual feed intake (RFI) identified 20 efficient R- chickens and 20 nonefficient R+ chickens. Residual feed intake was defined as the difference between observed feed intake (FI) and expected FI based on metabolic BW and BW gain, and was used as a measure for feed efficiency. Body weight and BW gain were similar for both groups. Feed intake and RFI were significantly higher in R+ birds. It is hypothesized that nonefficient R+ birds are more flexible to divert resources from production processes toward maintenance processes, thus being better capable of handling a bacterial challenge. Chickens of both groups were randomly allocated to immunization with heat-inactivated Salmonella enteritidis bacteria, or inoculation with live Salmonella bacteria. Transportation to the isolation units caused a decrease in FI in R+ birds. This may reflect a particular way of coping with stress in R+ birds. More R+ birds stopped bacterial shedding considering a nonshedding interval of 10 or 11 d (P = 0.041). Nonantigen-specific antibody responses against keyhole limpet hemocyanin (KLH) were higher in R- birds. We conclude that R+ birds are able to keep their metabolism at a higher level, as indicated by higher heart and liver weights, and that Salmonella infection leads to reduced heart, liver, and gizzard weights. Oviduct weight and number of small yellow follicles were reduced in infected birds. Antigen-specific antibody responses were not different between the groups, indicating high priority for this parameter as a life trait. Possible differences in stress susceptibility between efficient and nonefficient chickens need further examination.
- laying hen