Nutritional interactions with reproduction in birds.

Interaction from left to right, i.e. reproduction -+ nutrition, dominates the study of nutrition in domestic animals. Reproduction is thought of as generating a requirement for nutrients, which if not supplied results in less than optimum (usually maximum) production. In commercial systems the size and reproductive potential and therefore the nutrient requirements of birds are frequently changed by restricting growth during the rearing period. In table-egg-laying strains (layers) the change is not large but in broiler breeder hens the effect is dramatic. This is an example of nutrition -+ reproduction interaction and will be discussed later in this paper. There are four major components in the reproductive life-cycle of the bird (Fig. I). Man controls the environment of domesticated birds and maintains stable population sizes by removing eggs or young birds in much the same way as predators in the wild. The main determinant of domesticated survival is the economic production of eggs for both the table egg and broiler-meat industries. A simplifying model of nutrient responses for egg production, fertility, hatchability and early chick survival will be described first. Some apparent exceptions in broiler breeders fed on a limited quantity of feed to restrict growth during rearing will then be discussed.