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

1. Three experiments were carried out with White Rock (Anak) female ch icks 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 (SF R) 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 belo w 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 tim e significantly lower than those of the control birds throughout the e xperiments. Age at first egg was delayed in hens previously fed the LP D and tile diet containing the higher concentration of ZnO, and in tho se 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 signific ant effect was observed in only one experiment. 3. Egg production and egg size were not significantly affected by the various treatments, ex cept for the lower production in hens fed the LPD at an early age. 4. Negative regressions (on an individual basis) were consistently observ ed 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 obser ved between age at first egg and BW at that time. The regressions betw een BW at 22 weeks of age and number of eggs laid were positive but no t always significant. 5. Severe growth depression at an early age (pro duced by food restriction or ZnO supplemented diet, but not LPD) follo wed by decreased allocation of food afterwards, could provide a means for reducing BW of broiler breeder hens without adversely affecting eg g production. This procedure may save 2.5 to 6.6% of the food consumed during the life span of the birds.