Effects of dietary crude protein content and food intake on the production of semen in two lines of broiler breeder males.

1. The effects of dietary crude protein (CP) concentration and feeding rate on semen production and quality from 21 to 66 weeks of age were assessed in a factorial experiment with 48 caged broiler breeder males from 2 strains. 2. The probability of obtaining semen and semen volume were lower in one of the two strains but the concentration and yield of spermatozoa were similar. 3. There was no evidence that males which were fed on an increasing quantity of food produced more semen or a greater concentration of spermatozoa than males on a fixed allocation of 120 g/d food. 4. The concentration of spermatozoa was lower in males fed on a diet containing 160 compared with 120 g CP/kg. On termination of the experiment, average testes size was small and testicular function was absent in a large proportion of the males on the high protein diet.