Effects of age at photostimulation on reproductive efficiency and carcass characteristics. 1. Broiler breeder hens

The effect of age at photostimulation on carcass composition at photostimulation and at sexual maturity as well as its effect on subsequent reproductive performance in broiler breeders was investigated. A total of 600 broiler breeder pullets were reared in light-tight facilities. Skip-a-day feeding was used after 2 wk of age to limit body weight to levels suggested by the breeder. Limited daily feeding was initiated at the time of caging (time of photostimulation). The photoperiods used during rearing and lay were 8L:16D and 14L:10D, respectively. Forty birds were selected for study and moved to laying cages and photostimulated at 120, 130, 140, 150 or 160 d of age. Individual egg production records were kept until 60 wk of age. Twenty additional birds were killed for study of carcass composition and reproductive organ, morphology at the time of photostimulation and 20 others were killed at sexual maturity (first oviposition).As age at photostimulation increased, body weight and percent carcass lipid content increased while percent water and ash content decreased. No significant differences were found among treatment groups at photostimulation for carcass protein content. No significant differences were found in any carcass composition parameter at sexual maturity. All groups showed an increase in lipid content from photostimulation to sexual maturity, with the 120 d treatment group showing the largest increase. As age at photostimulation increased, the time from photostimulation to sexual maturity decreased. Total egg production, first egg weight, total egg mass produced, average fertility, hatchability and hatch of fertile did not differ significantly among treatment groups. Chick production was significantly higher in the 140-, 150- and 160-d treatment groups compared with the 120- and 130-d treatment groups. One explanation for the high rate of egg production seen in birds photostimulated at the older ages was that these birds reached sexual maturity with less between-bird variation. To take advantage of this improved flock uniformity, delaying photostimulation to 140 d of age or later is recommended. Key words: Chicken, broiler breeder, sexual maturity, egg production, hatchability, carcass composition