Abstract
Four experiments were conducted with the following objectives; i) To examine the effects of temperature and of the interaction of temperature, diet and feed form on the meat yield of broilers when birds are grown to a fixed age, ii) To investigate the effects of temperature and of the interactions of temperature and stocking rate on the meat yield of broilers when birds are grown to specific liveweights, iii) To assess whether retarded growth rate at high temperature affects breast meat yield in broilers.
Within the temperature range of 17-31.5°C, feed intake per day and growth rate declined linearly with rising temperature in this study. Rearing temperature did not affect the feed conversion efficiency, except when it declined severe heat stress in a humid and high stocking density environment.
When broilers were reared to 49 days of age at constant temperatures of 17°c, 21°c, 25°C and 29°C and fed on either of three diets a 13MJME/kg meal or a 13MJME/kg pellet or a 15MJME/kg meal pelleting and the high energy diet improved growth rate and feed conversion efficiency regardless of temperature. The breast meat proportion (as % of liveweight) obtained in male broilers was higher at 17°C or 25°C and lower at 21°C or 29°C, but in females it was highest at 17°C, intermediate at 25°C or 29°C and lowest at 21°C. But temperature or diet had no significant effects on the total meat yield and on the ratio of breast to dark meat. yielded 3.5% more breast meat than the males.
Female broilers
The
When birds were grown to specific liveweights at different temperatures (20.3-31.5°C), the ratio of breast to dark meat yield declined linearly Increasing rearing temperature with the rise of rearing temperature. decreased protein content, but increased fatness and dark meat yield and therefore the total meat yield reared in floor pens (20.3-28.7°C). rate of increase in fatness for each °C was higher in females than in males and higher at high stocking rate (515cm-/bird) than at low stocking rate (1030cm2/bird). The ash content of the carcass had no relation with temperature. Breast meat yield was higher in females than in males and higher at low stocking rate than at high stocking rate at all temperatures. In individually caged broilers (21.7°C-31.5°c), there was also a linear decrease in breast meat with increasing temperature, but no variation in fatness and in the total meat yield was attributable to temperature.
Birds restricted to 60% of normal growth rate through quantitive feed restriction had higher contents of total meat, protein and ash, and less fat in their carcasses, but the ratio of breast to dark meat yield obtained at slower growth rate was not different from that found in broilers fed ad- libitum to achieve maximum growth rate