Energy dynamics of broiler in thermoneutral or heat stress environments with different levels of metabolizable energyTwo experiments evaluated the effect of different levels of metabolizable energy (ME) on nutrient metabolizability, energy balance, and broiler performance under thermoneutral and cyclic heat stress conditions. A total of 672 male Cobb™ broilers were used, with ME levels of 2980, 3080, 3180, and 3280 kcal/kg in the diets. In a thermoneutral environment (experiment 1), higher ME levels improved the ether extract metabolizability coefficient, apparent metabolizable energy corrected for nitrogen balance (AMEn), and net energy (NE). However, increased ME from oil inclusion did not affect feed intake, apparent ME intake, retained energy, total and fasting heat production, caloric increment, or the efficiency of energy use for AMEn and NE. It did enhance weight gain, productive efficiency index, and feed conversion but reduced viability and increased feed cost per kg of live chicken. Under cyclic heat stress (experiment 2), the metabolizability coefficient of crude protein and ether extract rose with increased ME. Higher ME reduced the caloric increment up to an estimated 3021.5 ME and increased AMEn and NE. Improved feed conversion was noted, but feed cost per kg of live broiler also rose. In conclusion, the increase in energy levels positively affected the performance parameters of broilers from 20 to 41 days of age, particularly feed conversion, but it also raised production costs.
Key words:
respirometric chamber; digestibility; net energy; heat stress; caloric increment