Body weight and semen production of broiler breeder males as influenced by crude protein levels and feeding regimens during rearing.

An appropriate dietary CP level and feeding regimen during rearing is considered important for controlling BW and improving semen production in broiler breeder males. A total of 640 day-old broiler breeder male chicks of two commercial strains (A and B) received treatments of a factorial arrangement of two CP levels (12 and 16%) of corn-soybean grower diets and two feeding regimens [changing feed to a grower diet from the standard broiler starter at 0.45 and 0.68 kg BW and then skip-a-day feeding]. Four- to 28-wk BW differed between CP levels during rearing, with heavier BW on the 16% CP diet than on the 12% CP diet in spite of isocaloric feed intake. Strains did not show a significant difference in BW prior to 40 wk of age. Feed restriction initiated at 0.45 or 0.68 kg BW had no effect in controlling BW after 4 wk of age. Uniformity of BW did not differ between CP levels. Semen volume was greater on the 12% than on the 16% CP diet from 28 to 36 wk of age. Semen concentration was not affected by CP levels, feeding regimens, or strains. Spermatozoa per ejaculate from 28 to 52 wk of age was correlated negatively with 8- to 20-wk BW. This negative relationship was attenuated with age, until at Week 46 or later spermatozoa per ejaculate was associated positively with BW after sexual maturity. No difference in percentage of males in semen production was noted between strains, CP levels, or feeding regimens. In brief, diet changes at 0.45 or 0.68 kg BW were not important in improving semen production, whereas the low CP diet (12%) had advantages in semen production over the high CP diet (16%). A negative relationship existed between semen production and BW during rearing; however, continued BW gain after sexual maturity was necessary to optimize semen production, especially during the late breeding period.