Abstract
The present study aimed to compare the dynamics of growth of various chicken genotypes exposed to heat stress, low-input diets, and free-range farming by using Gompertz model to gain insights into their capabilities to face environmental and nutritional challenges. Three in vivo trials (T1: heat stress, T2: low-input diets, and T3: free-range system) were conducted, involving a total of 671 animals. Five chicken genotypes were employed in each trial: 2 Italian local breeds, Bionda Piemontese (BP) and Robusta Maculata (RM), along with their crossbreeds with Sasso hens (BP×SA and RM×SA), and a commercial hybrid (Ross 308). One-day-old male chicks were individually identified, and the 5 genotypes were randomly allocated to different challenging conditions: T1 involved 2 environmental temperatures (thermoneutral vs. high temperature); T2 involved 2 diets (standard vs. low-input); T3 involved 2 rearing systems (conventional vs. free-range). The chickens were weighed once a week from their arrival until slaughtering, and the data were used to build growth curves using the Gompertz model. Chickens from different genotypes were slaughtered at varying ages based on their maturity. In all trials, the challenging conditions significantly reduced adult body weight (A; -31.0%) and maximum growth rate (MGR; -25.6%) of Ross chickens. In contrast, in T1 and T2, no significant changes were observed in the main growth curve parameters of local breeds and crossbreeds, while under free-range conditions, there was even an increase in the A and MGR of these genotypes. The crossbreeding was effective in increasing A and MGR of BP (+30.5% in BP×SA), as well as in improving the precocity and MGR of RM (+19.5% in RM×SA). Our findings highlight the effectiveness of the Gompertz model as a tool for evaluating birds' adaptability and confirm the greater ability of local breeds and crossbreeds to adapt to different challenges. In conclusion, our methodological approach could be used to choose the genotype most suited to the environmental context and confirm the potential advantages of crossbreeding for enhancing resilience and sustainability.
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