Performance of two male broiler breeder strains raised and maintained on various constant photoschedules

The purpose of the present study was to examine the interaction of constant photoschedules and genetic background on performance of male broiler breeders. Day-old cockerels from two BW strains were placed on litter floors in light-controlled chambers. Light treatments (LT) (60 lx) consisted of 2, 4, 8, 16, and 24 h light/day. At 9 wk of age, birds were individually caged and evaluated biweekly for semen production. Venous blood samples were collected at 16, 32, 48, and 64 wk of age. Data for testes weight, histology, and morphometry were obtained at 64 wk. Age at first semen production showed a cubic response in the levels of LT with earliest semen production from 4 and 8 h light (187.0 and 188.2 days, respectively). The BW was linear in the levels of LT within week; average BW was generally greater for birds on short LT than for birds on longer LT. Semen concentration was also linear in the levels of LT within week; increased semen concentration occurred with short LT. Changes in semen weight and spermatozoa count per ejaculate across the levels of LT differed for strain. A larger percentage of males produced semen in the less than or equal to 8 h LT than in the 16 or 24 h LT. Plasma testosterone was lower at 16 wk compared with later ages, and a positive linear relationship existed between testosterone level and hours of light. There was a cubic LT effect for testes weight per BW with larger values for less than or equal to 8 h LT compared with 16 or 24 h LT.