Genotype by nutrition interactions for immunoresponsiveness and disease resistance in chickens

This dissertation involved a series of in vivo experiments to measure growth, immunoresponsiveness, and disease resistance in several genetic stocks maintained under different nutritional regimens. Genetic stocks included (1) a commercial layer line, (2) commercial broiler lines, (3) a White Rock line selected for high juvenile body weight, (4) a White Leghorn line selected for low antibody response to sheep erythrocytes, (5) a fast growing White Rock dwarf line, (6) a slow growing White Rock dwarf line, (7) a cross of 3 X 4, and (8) reciprocal crosses of 5 X 6. The nutritional regimens were either alternate-day (AD) and ad libitum (AL) feeding or high (E) and low (A) nutrient density.

As expected, within a feeding regimen males were heavier than females and within a sex, AL chicks were heavier than AD chicks. Also, chicks fed Diet E were heavier than those fed Diet A. For traits associated with body weight there were significant feeding regimen by sire family interactions which was due to differences among sires in the magnitude of AD:AL relationship. Heterosis for body weight was consistently higher in males than females regardless of feeding regimens and higher for AD than AL chicks suggesting that the degree of heterosis was age and environment dependent.

Immunocompetence as measured by production of antibody against sheep erythrocytes (SRBC) was higher for chicks fed AD than AL. In one experiment there was a significant diet by stock interaction for SRBC antibody titers. The interaction was because the commercial broilers fed Diet A had higher SRBC antibody titers than those fed Diet E, while the pattern for diets reversed in commercial layers. This suggested that the allocation of nutritional resources towards growth and immune response was not independent of the previous selection history of the population. Also, influence of genetic factors on antibody production was evident as there were differences among sire families in antibody titers to SRBC. In addition, heterotic effects for SRBC antibody were evident as titers were higher for the 3 X 4 crosses than lines 3 and 4 and titers were higher for the 5 X 6 crosses than lines 5 and 6.

In faster growing genetic stocks responses to E. coli inoculation as measured by mortality and severity of cardiac and air sac lesions were greater for chicks fed AL than AD. For chicks fed AD lesion scores were lower for those without access to feed for the 24-h period immediately after challenge. When AD chicks were released to ad libitum feeding for several days and then inoculated, lesions were more severe than for AL and AD chicks. This result demonstrated that chicks from lines selected for rapid growth tended to allocate a greater proportion of resources to growth which reduced their ability to adjust rapidly to a disease challenge. Genetic factors influencing the response to E. coli inoculation were also evident as lesions were less severe for cross chicks than for their parental lines.