Effect of Stocking Density on Selected Blood Physiological, Biochemical and Enzymatical Variables of Broilers Grown to 3 kg under Antibiotic-free Conditions

Background: Reducing stocking densities may play a key role in minimizing difficulties such as physiological welfare when reducing or ending antimicrobials in poultry diets. As the demand for poultry and associated products increases, one of the major concerns centers on the question of whether stocking density influences welfare responses that are characteristic of physiological welfare. This study investigated the effect of stocking density on selected blood physiological variables along with plasma biochemistry variables and enzymes activities of broilers fed antibiotic-free diets grown to 3 kg. Methods: A total of 888 1-d-old Ross ´ Ross 708 chicks were randomly distributed into 24 pens based on stocking density treatments assignment. The treatments consisted of 4 densities (29, 33, 39 and 42 kg/m2) with six replicates. Treatments were blocked within the room to account for any variations in room conditions. Treatment assignments were randomized within each block. Used litter bedding was obtained from commercial farms to mimic commercial conditions and litter microflora. Birds were provided a three phase-feeding program (Starter: 0-14 d, Grower: 15-28 d and Finisher: 29-42 d) antibiotic-free diets. Feed and water provided ad libitum. Blood samples were collected from the brachial wing vein of 3 males and 3 females’ birds per pen on d 28 and 42 and analyzed immediately for blood physiological variables. Blood plasma samples were analyzed for T3, T4, corticosterone, biochemical variables and enzyme activities. Result: The only effect of stocking density was observed on partial pressure of CO2 (pCO2) and uric acid which were within physiological ranges for this species. However, blood glucose and plasma corticosterone concentrations were not affected by stocking density, suggesting no signs of physiological stress. Stocking densities up to 42 kg/m2 with proper environmental management may be suitable for both poultry integrators and contract growers to enhance broilers production efficiency without compromising the welfare of broilers grown to 3 kg body weight.