Characterisation of the growth curve of free-range turkeys using linear and non-linear models in locally adapted versus commercial hybrid genotypes

Organic and free-range farming are becoming increasingly common practices in the turkey meat industry, although limited research has been conducted in uncontrolled environments. Therefore, the present work aims to define the growth pattern of an indigenous landrace and a commercial strain grown outdoors in southern Spain. To achieve this aim, the weights of Andalusian turkeys (1,826 and 1,797 records for males and females, respectively) and commercial toms (584 records) were recorded to test 19 linear and nonlinear mathematical functions. The suitability of the models was defined using the coefficient of determination (pseudo-R2), mean squared error, the Bayesian information criterion, the Akaike information criterion, and the corrected Akaike information criterion. 17, 16, and 13 models out of 19 fitted the growth curves of Andalusian females, Andalusian males, and commercial males, respectively. Most of the models showed Pseudo-R2 values greater than 0.90. According to the sigmoid models, the asymptotic weights were estimated to be close to 11.5, 5.5, and 23.0 kg for Andalusian males, females, and commercial males, respectively. The Andalusian females showed the earliest precocity at inflection and optimal slaughter age (3 and 5 months, respectively), while the Andalusian males showed the latest precocity (4 and 7 months, respectively). As expected, based on literature on other fast-growing strains, the commercial flock exhibited the greatest weight (8.96–11.44 kg) and growth rates (143.30–210.38 g/day). However, delayed ages at inflexion and optimal slaughter (3.7 and 5.8 months, respectively) and lower maturity indexes were obtained compared to those in the bibliography. On the other hand, the age at inflection and maturity indices of Andalusian birds were similar to those of the commercial flock, in line with reports on other local breeds. Therefore, the environment had a significant impact on commercial birds reared outdoors, reducing their growth potential and efficiency. On the other hand, the growth of Andalusian birds seemed unaffected.