Feed restriction.

Abstract

It is common practice to control the feed consumption, and therefore the energy intake, of the parents of commercial broilers and ducks but not turkeys. Genetic selection for high rates of body weight gain results in correlated increases in ovulation rate and disrupted production of eggs with sound shells suitable for hatching. Feed restriction controls multiple ovulation in broiler breeders and ducks but not turkeys. The reasons for these breed and species differences and the biological principles underlying the allocation of feed energy are outlined. A series of experiments provided the basis for a theory of feed restriction in broiler breeders and led to the development of a stochastic model to predict egg production. Research has shown that achieving the target body weight at the onset of lay is critical and that feed supplied after the onset of lay should be adequate to support the peak of egg production. Feed allocation after the peak of egg production has been reached can be gradually decreased to match the requirements for lower egg production and to limit the effects of excessive body weight gain on mortality and productivity. Feed restriction is not practised in turkey breeders because it does not control the ovarian hierarchy and persistency of lay is poor, probably because the birds naturally lose a considerable quantity of body weight after the onset of lay. Conversely, excessive weight gain is undesirable and turkeys are fed low-energy and low-protein diets to limit body weight gain before photostimulation. The body weight of broiler breeder cocks and drakes is substantially limited during rearing to enhance mating efficiency and fertility. Low-protein or low-energy diets are used to limit excessive body weight gain in stags as this facilitates semen collection and improves health. In males of all three species, body weight is allowed to increase slowly during the mating period to maintain fertility. The welfare consequences of feed restriction in breeding birds are discussed and alternatives to quantitative feed restriction are outlined. It is concluded that the long-term solution to the need for substantial feed restriction in breeding birds is genetic selection for a decreased propensity of multiple ovulation.