Body growth description of male and female from three broilers strains in hot climates
The body growth description is a useful tool for poultry industry's sectors, and factors like the genotypes and environment may affect this growth. The purpose of this study was to describe the body growth of male and female from Cobb 500, Ross 308 and Hubbard Flex. In total, 2,160 chicks were used, being the treatments distributed in an experimental design completely randomized in factorial arrangement (3 strains and 2 sexes) with six replicates of 60 birds each, at a stocking density of 30 birds/m?. The average temperature, minimum and maximum and relative humidity inside the shed during the experimental period were 28.1 ? 0.7 ? C; 22.0 ? 1.2 ? C; 34.2? 0.9 ? C and 73.6 ? 13.7%, respectively. The birds were weighed weekly, being selected a sample birds with weight close to the average weight of each pen (? 5%) for slaughter. The birds were fasted for 24 h and reweighed. There were fitted Gompertz equation for each strain, in each sex, to the fasted body weight (FBW). To verify the strain effect on the Gompertz curves parameters, weight at maturity (Wm), rate of maturing (B) and the time at which maximum growth rate is attained (t*), of FBW assessed within each sex, tests have been conducted to verify the equality of parameters and identity of non-linear models, as proposed by Regazzi (2003). The tests models were: no parametric restriction (?), parameter Wm in common (?1), parameter B in common (?2), parameter t* in common (?3), parameters Wm e t* in common (?4), parameters Wm e B in common (?5) and all parameters (Wm, B, t*) in common (?6). For the FBW, regardless of sex, the model ?2 was the most appropriated to describe the growth of birds, being the parameter B common between the strains (0.035 and 0.038 g/d/g for males and females, respectively). Males Hubbard showed the highest Wm (5607. 8 g ) and t* (43 d), following the males Ross (Wn = 5458.3 g and t* = 42.8 d) and Cobb (Wn = 4975.1 g and t* = 41.7 d). In the same way, the females Hubbard showed the highest Wm (4437.4 g) and t* (39.1 d), following the females Ross (Wn = 4119.5 g and t* = 38.4 d) and Cobb (Wn = 3900.4 g and t* = 37.3 d). The results showed that the strains have particularities in their growth, for this reason the choice of strain might be directed according the production goals.