Protein Levels in Growing Diets and Reproductive Performance of Cockerels

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Abstract
Two experiments were conducted with Single Comb White Leghorn cockerels to determine the effect of dietary protein during the growing period on sexual maturity and various reproductive characteristics. Dietary protein levels of 16.0, 9.0, 6.75 and 4.5% were fed beginning when the cockerels were 9 weeks of age and 7 weeks of age in experiments 1 and 2, respectively. A 17% protein breeder diet was fed from 23 weeks until 37 weeks of age. Body growth was depressed with each decrease in dietary protein. The 4.5% protein level approximated a maintenance diet. Sexual maturity was delayed in the low protein groups, without apparent permanent damage to the reproductive system. After the recovery diet had been fed for 7 weeks, there was little difference between dietary groups in the number of birds producing sperm or in semen scores. By the end of the recovery period the low protein groups had higher sperm concentrations and greater testes weights. Fertility was higher in the 9.0 and 6.75% protein groups than in the 16.0 and 4.5% protein groups at the end of the recovery period. Hatchability of fertile eggs was not affected by protein levels during the growing period.