Resource allocation in chickens: genetic and nongenetic influences on development, growth and reproduction

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Virginia Polytechnic Institute and State University


Genetic and nongenetic influences on organ development in chickens were studied. Populations included lines divergently selected for juvenile body weight, reciprocal F₁ crosses between them, and a commercial broiler-breeder parent line segregating for early and late feathering alleles. Nongenetic influences included restricted and ad libitum (AL) feeding regimes.

Positive correlated responses to selection for body weight included proportionally larger breast, legs, fat depots and small intestine. Negative responses included fecundity, feather and gizzard weights. The degree of non-additive genetic variation differed among traits but reciprocal effects were negligible. Weights and lengths of organs at specific ages did not necessarily reflect the situation at common body weights suggesting differences in resource allocations among populations. In commercial meat-type chickens, AL feed consumption was near gut capacity and increased rapidly to approximately 140 days of age. Concomitantly, body weights increased to approximately 130 days and then plateaued.

Influences of early and late feathering alleles were minor except for weights of feathers. Alternate-day feeding prior to sexual maturity reduced weights of fat depots, feathers and muscles and increased size of the gastrointestinal tract. Effects of every day, skip-one-day and skip-two-day restrictions of feed were generally similar. Chickens adapted quickly to restricted feeding but, when released to AL feeding allocated resources into growth. This reallocation reduced their resistance to an Escherichia colichallenge. Prior to sexual maturity, relative weights and lengths of the gastrointestinal tract decreased with age and relative sizes of fat depots and muscle increased with age. Thereafter relationships of most organs to body weight remained stable. Restricted chickens adapted to fasts by maintaining exogenous energy stores (gastrointestinal tract contents) for longer periods. Unlike those fed AL, they did not became obese and their livability and fecundity were greatly enhanced.