Three hundred commercial Single Comb While Leghorn (SCWL) pullets of two strains differing in age at first oviposition (early maturing = EARLY; later maturing = LATE) were reared and photostimulated at 18 wk. Selected birds of each strain were killed at weekly intervals from 17 to 23 wk, at sexual maturity, or at 68 wk of age for the study of carcass and reproductive organ traits. Egg production was recorded for surviving hens to 68 wk of age. The two strains differed in age at sexual maturity (EARLY, 137.5 d; LATE, 142.1 d). The EARLY strain birds appeared to allocate a greater proportion of nutrients to reproductive development (oviduct) from 19 to 22 wk of age than did the LATE group, which showed greater breast muscle development during this same period. The LATE strain hens were significantly heavier than the EARLY hens at sexual maturity, and this difference in BW persisted to the end of the laying period. Although total egg production did not differ between strains, the LATE strain hens had a longer prime egg-laying sequence length (LATE, 70.2 d; EARLY, 52.6 d) as well as a longer mean sequence length (LATE, 12.8 d; EARLY, 8.7 d). Egg weight did not differ between strains. These data suggest that LATE lines of egg-type hens offer equivalent production efficiency due to improved rates of lay, albeit starting later.
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