Attempts to achieve low‐weight broiler breeder hens by severe growth depression during various periods up to 6 weeks of age and food allocation below the recommendations thereafter

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Abstract
1. Three experiments were carried out with White Rock (Anak) female chicks to evaluate the possibility of obtaining low‐weight breeder hens and to assess their reproduction potential. Such hens were obtained by early growth depression induced by either severe food restriction (SFR) from 1 or 2 to 3 or 4 weeks of age, or a low‐protein diet (LPD) fed from 0 to 6 weeks of age, or the use of diets containing 0·7 or 0·8% zinc as ZnO from 1 to 3 weeks of age, followed by food allocation below recommendation up to 22 or 67 weeks of age. 2. Body weights (BW) of the birds whose growth had been depressed were consistently and at time significantly lower than those of the control birds throughout the experiments. Age at first egg was delayed in hens previously fed the LPD and the diet containing the higher concentration of ZnO, and in those exposed to SFR from 2 to 4 weeks of age. BW at that time tended to be lower in birds whose growth had been depressed, although a significant effect was observed in only one experiment. 3. Egg production and egg size were not significantly affected by the various treatments, except for the lower production in hens fed the LPD at an early age. 4. Negative regressions (on an individual basis) were consistently observed between BW at 22 weeks of age and age at first egg, and between age at first egg and number of eggs laid. Positive regressions were observed between age at first egg and BW at that time. The regressions between BW at 22 weeks of age and number of eggs laid were positive but not always significant. 5. Severe growth depression at an early age (produced by food restriction or ZnO supplemented diet, but not LPD) followed by decreased allocation of food afterwards, could provide a means for reducing BW of broiler breeder hens without adversely affecting egg production. This procedure may save 2·5 to 6·6% of the food consumed during the life span of the birds.