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Abstract
The reproductive development of 2 meat strains (Cobb 500 and Cobb MX) of broiler breeder males provided different levels of total feed intake during rearing was evaluated. Six hundred day old cockerels from each strain were divided among 4 feeding treatments (full fed; and concave, standard, and convex restricted feed levels) with each treatment and strain housed separately. The concave and convex feeding treatments were 5-10% above and below standard strain guidelines. All cockerels were full fed to 3 weeks of age, with the 3 feed restricted treatments implemented at 22 days and continued to 20 weeks of age. At 21 weeks of age 44 cockerels from each restricted feeding treatment and strain were moved to individual cages, photostimulated and fed to maintain target body weight. Total testes weight relative to total body weight was greater in the full fed cockerels than the restricted fed birds after 8 weeks of age. There were no differences in relative testes weight between any of the feed restricted birds. For the entire rearing period, the overall relative testes size was greater for the MX males. Regardless of the feeding regimen total testosterone concentrations reached detectable levels 2 to 4 weeks earlier in the MX males than the Cobb 500 males. The ontogeny of detectable plasmatestosterone levels was also negatively correlated with total feed intake. The results suggest that sexual maturation in the MX strain may occur at a faster rate than in the Cobb 500 strain.