Effects of dietary energy levels on performance and carcass yield of two meat- type broiler lines housed in hot and cool ambient temperatures

Abstract Two meat-type broiler lines, Line A and Line B were fed experimental diets from 22-42d with objectives to determine the effects of dietary metabolizable energy (ME) levels on feed intake (FI), performance, body composition (BC), and processing yield as affected by environmental grow-out temperatures. Two thousand and fifty male chicks from Line A and 2,050 male chicks from Line B were reared in 90-floor pens, 45 chicks per pen utilizing primary breeder nutrition and husbandry guidelines for starter (1-10d) and grower (11-21d) phases. Experimental finisher diets consisted of five increasing levels of apparent nitrogen corrected ME (2800, 2925, 3050, 3175 and 3300 kcal/kg set at 19.5 % crude protein and 1.0 % dLys at each level) to represent 80, 90, 100, 110, and 120 % ME of Evonik AminoChick® energy level giving 2 X 5 factorial design and were fed from 22-42d. All other amino acid levels in diets were formulated to a fixed ratio of dLys level. There were nine replicate pens for each diet and each line. The experiment was conducted twice – once in hot season (barn averages: 77.55 ˚F and 86.04 % RH) and another in cool season (barn averages: 69.91 ˚F and 63.98 % RH) of the year. Results showed that FI and feed conversion ratios (FCR) decreased (P 0.9). However, there was no difference (P > 0.05) in % weights (of live weight) for wings, breast filet, tenders, or leg quarters across ME levels for both lines except % fat pad that increased (P 0.05), whereas higher BW and improved FCR were observed for Line A. Line A had higher % fat mass in both seasons. In summary, performance and yield results as affected by dietary ME levels were line specific and were affected by grow-out seasons. The optimal dietary ME level for the ME range studied (2800-3000 kcal/kg) at a constant recommended amino acid level lies in determining the best performance and profitability indices by taking into account the grow-out production inputs and processing yield outputs.