PROTEIN LEVELS IN GROWING DIETS AND REPRODUCTIVE PERFORMANCE OF COCKERELS.

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 die tary protein. The 4.5% protein level approximated a maintenance diet. Sexual matur ity 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 grow ing period. Recent reviews indicate that a marginal level of protein in the diet of laboratory animals may delay or inhibit the develop ment of the male reproductive system and depress fertility (1, 2). However, rela tively little work has been reported con cerning the relationship between nutrition and reproduction in male chicks. Parker and Arscott (3) have shown that energy restriction of adult male chickens reduced volume and fertilizing capacity of semen, and reduced body and testes weights. Parker and McSpadden (4) demonstrated that feed restriction resulted in decreased fertility, semen volume, sperm concentra tion and motility in adult male chickens. A recent report by Arscott and Parker (5) indicated that dietary protein levels of 10.7 and 6.9% fed to adult males had no detri mental effect on fertility or hatchability as compared with the 16.9% level. In fact, fertility was higher in the 6.9% group than in the 16.9% group. Protein restric tion has been reported to delay sexual ma turity in females (6). This study was con ducted to determine the effects of low levels of dietary protein during the grow ing period on the reproductive perfor mance of cockerels. EXPERIMENTAL Experiment 1. Seventy-two Single Comb White Leghorn (July-hatched) cockerels were placed at random into 12 repli cates of 6 birds each. Three replicates were fed each experimental diet. Four ex perimental diets were fed which were cal culated to contain 16.0, 9.0, 6.75 and 4.5% protein, respectively. The composi tion of the 16.0 and 9.0% protein diets is shown in table 1. The other 2 diets were formed from the 9.0% diet by dilution with glucose monohydrate.3 When dilu tions were made, increased levels of ground limestone, defluorinated phosphate and the micro-ingredient premix were added to maintain constant levels of cal cium, phosphorus, and supplemental vita mins. The cockerels were placed in finish ing batteries at 9 weeks of age and fed the experimental diets and water ad libitum for 14 weeks. Prior to being given the ex perimental diets, the cockerels had been Received for publication July 6, 1964. 1 Florida Agricultural Experiment Stations Journal Series no. 1900. 2 Presented in part before the meeting of the Poultry Science Association, August, 1963 (Poultry Sci., 42: 1319, abstract), and August, 1964 (Poultry Sci., 43: 1377, abstract). 3 Cerelose, Corn Products Company, Argo, Illinois. J. NUTRITION, 85: '65 29 by gest on July 3, 2011 jn.nition.org D ow nladed fom 30 WILSON, WALDROUP, JONES, DUERRE AND HARMS