Níveis de proteína na dieta para frangos de corte criados em termoneutralidade e estresse cíclico por calor

Abstract

Two experiments were conducted in order to evaluate the influence of protein diets (16%, 18%, 20% and 22% CP) on physiological parameters, metabolism and performance of broilers raised in thermoneutral environment (23 ± 2°C; 60 ± 2% RH) or heat stress (32 ± 2°C; 60 ± 2% RH). 360 male broilers were used, Cobb, from 22 to 42 days years old. Birds were installed in a climatically room. The physiological parameters evaluated were respiratory rate (RR), rectal temperature (RT), blood gas analysis, blood biochemistry and heterophil / lymphocyte. Were used to estimate the dry matter digestibility coefficients (DMDC), crude protein (CPDC), fat (EEDC), the values of AME, AMEn, MEm, and NE, beyond the performance parameters: feed intake, weight gain (BW), feed convercion (CF) and viability. In both trials, the experimental design with split plot, being the diet of the plot and the age of evaluation, the subplot. For the digestibility determinations, power and performance we used the completely randomized design with four trataments and six repetitions with 15 birds / each. In the first experiment (thermoneutral), the RT was not affected by CP levels of the diet, but by the age of the birds. Since the RR of the broilers was affected by diet, and the level of 22% CP in the diet caused a significant increase in RR from 16 and 18% CP. For biochemical parameters, there was only an increase in total cholesterol levels in olders broilers chickens, there was no significant effect of diets for these variables. The crude protein levels in the diet did not influence the total leukocytes levels, heterophilis, lymphocytes and consequently the heterophilis / lymphocytes rate was also not affected. There was better digestibility of CP with the most protein diets (20 and 22% CP) relative to the order (16 and 18% CP), with reflected the values of AME and NE, improving performance of the birds in BW and CF at 42 days years old. In the second experiment (heat stress), the results showed influence of high ambient temperature on the RR and RT, regardless of diet. The levels of total leukocytes were not affected by crude protein in the diet. But the age of the birds due to the cyclical heat exposure time, reflected in increased production of total leukocytes in broilers with 32 days of age and more to stress exposure time, showing a reaction of the immune system to the stressor. With respect to metabolic parameters and performance, reduced levels of crude protein diet, from 22% to 16% with the amino acid supplementation, and impaired the CPDC, EEDC, decreasing the energy available to the broilers, demonstrated by the worst results of BW and CF at 42 days years old on cyclic heat stress from 30°C to 34°C. Thus, it was concluded that the amino acid correction used in the feed of 16% CP, was not able to reflect the same performance in poultry in relation to the diet with 22% CP in the heat.