THE EVALUATION OF THE GROWTH-PARAMETERS OF 6 STRAINS OF COMMERCIAL BROILER-CHICKENS

1. An experiment was conducted to measure the potential growth of male s and females of 6 commercial broiler stocks, from which information t he growth rates of these genotypes could be characterised by the Gompe rtz growth equation. 2. Feeding and environmental conditions were desi gned to ensure that the birds remained comfortable throughout their gr owing period, which was to 26 weeks of age. A choice of diets differin g in protein content was offered from 3 weeks of age. Because of leg w eaknesses among the male broilers after 11 weeks of age, and because m any females reached sexual maturity at about this age, the growth anal yses were conducted on weights collected up to 11 weeks of age only. A t this weight, broilers had achieved approximately 0.76 of their matur e weight. 3. Birds representative of each genotype were killed for car case analysis at weekly intervals to 9 weeks of age, and every two wee ks thereafter. The contents of gut fill, feathers, water, protein, ash and lipid were measured on each of these birds; from these, equations were derived for each genotype that allowed the estimation of the wei ghts of these components in the birds remaining on the experiment. 4. The body weight, body protein, body water and feather weight of the 12 genotypes were described in terms of the mature weight of these compo nents, their rates of maturing and the time taken to reach the maximum rate of growth of each component. These descriptors of the growth of each component were then compared between genotypes. 5. No statistical ly significant differences existed in the rates of maturing of the dif ferent genotypes, either between strains or between sexes. Highly sign ificant differences were evident between strains and between sexes in their mature weights, indicating that their rates of growth differed. 6. Estimates of mature feather weights indicated that this component o f the body comprised 0.062 and 0.050 of the mature body weight of fema le and male broilers respectively. The protein content of feathers inc reased steadily, and the water content decreased steadily, throughout the growing period. 7. Differences between the genotypes evaluated in this experiment indicate that the nutrient and environmental requireme nts of these genotypes would differ. A description of each genotype, t herefore, is an essential component of any simulation model that attem pts to determine the optimum economic feeding programme and environmen tal conditions for broilers.