Evaluation of the potential growth and body composition of the Cobb 700 genotype.

1. The potential growth of the chemical and physical components of males and females of the Cobb 700 strain was measured from hatch to 15 weeks of age.2. A four-phase ad libitum feeding programme was used to feed 200 chicks of each sex. All birds were weighed weekly. Ten birds per sex were sampled at 0, 7, 14, 28, 42, 56, 70, 84 and 105 d of age. They were weighed before and after plucking to determine the weight of feathers. Physical parts were measured on defeathered birds, whereafter these components were combined, minced, freeze dried to measure water content, and then analysed for protein, lipid and ash content.3. Mature body weights of males and females averaged 8.38 and 6.94 kg, respectively, mature body protein weights averaged 1.48 and 1.19 kg and mature body lipid contents averaged 1.08 and 1.54 kg, respectively.4. Rates of maturing of the empty feather-free body weights of males and females averaged 0.0417 and 0.0402/d, respectively. All chemical and physical components within a sex, other than feathers, had the same rate of maturing. The rate of maturing of feathers, calculated by iteration, in males was lower than in females (0.0324 vs. 0.0357/d) and the mature weight was higher (435 vs. 372 g).5. The ratios of the chemical components to feather-free body protein at maturity for males and females were, for water, 3.80 and 3.34; for lipid, 0.73 and 1.29; and for ash, 0.13 and 0.19, respectively. Separate equations were required for males and females to describe the allometric relationship between lipid and protein in the feather-free body.6. Mature body weights of broilers in this trial were considerably higher than those measured using the same protocol 28 years ago, whereas rates of maturing have remained the same.

The response of turkeys to dietary balanced protein during two periods of growth.

1. Two experiments were conducted to measure the response of growing turkeys to dietary protein content. In the first, 960 sexed British United Turkey (BUT 6) poults were used to measure the response to balanced protein from 3 to 6 weeks of age. In the second, 1440 sexed BUT and Hybrid Converter poults were raised from 14 to 17 weeks.2. In both experiments, six levels of dietary protein were fed, with feed intake, body and feather weight gain and changes in body composition measured. The levels of protein chosen ranged from 0.53 to 1.2 of the Aviagen requirements for growing turkeys.3. In the first experiment, six poults were sampled from each sex at the start of the experiment for carcass analysis, and four were sampled from each strain and sex in the second. At the end of each experiment, eight poults from each treatment were sampled. Body composition analyses were made on individual defeathered birds.4. Weight gain increased linearly with protein intake in the early period and exponentially in the later period. In both periods, feed intake decreased as protein content reduced.5. In the early period, body lipid content increased from 20.2 to 41.5 g/kg body weight, as dietary protein content decreased, but there was no change in the later period. Efficiency of utilisation of dietary protein declined linearly with an increase in dietary protein content, from 0.87 to 0.46 g/g in the first, and from 0.43 to 0.27 g/g in the later period.6. The inability of the growing turkey to increase feed intake on marginally limiting feeds may have been due to a genetic constraints to store excess energy consumed as body lipid, resulting in the observed decrease in feed intake as dietary protein content is reduced.