Níveis de energia metabolizável em rações para frangos de corte em ambiente de conforto térmico ou sob estresse por calor

Abstract

Two experiments were performed to evaluate the effect of different levels of ME (metabolizable energy) in the diet on performance, physiological and metabolic parameters of broilers submitted to environmental conditions of thermoneutrality (TNE: 23 ± 2 °C, 60 ± 2% RH) and cyclic heat stress (CHS: 23-32 ± 2 °C; 60 ± 2% RH). We studied 336 Cobb male broilers in the growing phase in each experiment. The diets used in both experiments were isonutritives, except for ME, which were as follows: 2980, 3080, 3180 and 3280 kcal/kg in the diet. In the first experiment, physiological, biochemical and hematological parameters ofchickens raised in TNE did not influence the levels of ME. Age affected the pH, HCO3 -, HB, Hct, Na+, K+, GLU, CHOL, TRI, LAC, PT, LEUC, HET, LYMP and H/L of broiler raised in TNE. The increase in the level of ME reduced the relative weight of gizzard, spleen, and liver plus gallbladder, however, it did not affect the relative weight of other evaluated organs. MElevels improved the digestibility of ether extract (EE) for broilers raised in TNE. Increased ME obtained by the inclusion of oil in the diets did not show any effect on the apparent ME consumption corrected by the nitrogen balance (AMEn), retained energy, total heat production, heat production in fasting, heat increment (HI), efficiency of use of crude energy (CE) for AMEn and efficiency of utilization of AMEn for net energy (NE) in broilers in TNE. The feed intake and feed cost per kg of live broiler in the period of 19 to 41 day-old showed no difference between the treatments. The weight gain (WG), the daily consumption of ME and productive efficiency index (PEI) increased, while feed conversion (FC) and viability decreased with increasing levels of ME for broilers in TNE. In the second experiment, the levels of ME affected only the partial pressure of carbon dioxide (pCO2), without influencing the other physiological, biochemical and hematological parameters of broiler in CHS. Ageaffected pH, pCO2, HB, Hct, GLU, CHOL, TRI, LAC, PT, ALB, LEUC, HET, LYMP and H/L of broilers in CHS. ME levels increased the relative weight of the gut, but did not influence the relative weight of other organs. The digestibility of crude protein and EE increased with the increasing of ME levels for broilers in CHS. The increase of ME reduced the HI up to the ME level of 3151.72 in the diet and increased the AMEn and the NE of broilers fed in CHS. The increase of ME in the diet improved the FC and increased the cost of feed per kg of live broiler raised under CHS.