An index for the estimation of chicken adaptability to free-range farming systems of different slow-growing genotypes

Simona Mattioli^1,2*Laura Menchetti³Elisa Angelucci²Alice Cartoni Mancinelli²Alessandro Dal Bosco²Laura Madeo⁴Francesca Di Federico²Luigia Bosa²Livia Moscati⁴Cesare Castellini²

• ¹University of Perugia, Perugia, Italy
• ²Department of Agricultural, Environmental and Food Science, University of Perugia, Perugia, Italy
• ³School of Biosciences and Veterinary Medicine, camerino, Italy
• ⁴Istituto Zooprofilattico Sperimentale dell'Umbria e delle Marche Togo Rosati, Perugia, Italy

Estimation of chicken adaptability to extensive rearing system (ERS) is a complex issue, many aspects should be considered: natural and/or welfare-based behaviours, kinetic and foraging attitude, resistance to environmental changes (i.e., thermotolerance) and to the disease. However, it is necessary to find a rapid and straightforward way to define the degree of adaptation of a chicken genotype in a commercial farm context. With this purpose, the objective of the present research was to develop an index of adaptability constituted by few and simple traits. Two-hundred chickens of four different slow-growing genotypes (SGs; 25 chickens x 2 replicates x genotype) were outdoor reared: Red JA57 (RJ), Naked Neck (NN), Lohmann Dual meat-type (LD), and an Italian Crossbreed (Robusta Maculata x Sassò, CB). Behavioural observations were recorded 2 times/week on outdoor pens from 36 to 81 days, whereas plumage condition, hock burns, footpad dermatitis, blood parameters, proximate composition and technological traits of breast and drumstick meat were recorded at slaughtering age (81 days) from 15/chickens genotype. On-farm productive performance were recorded weekly. The almost 200 variables collected were classified into four pillars (i.e., behaviours, body conditions, meat quality, in vivo health) and reduced into 9 main variables by using Discriminant (DA) and Principal Component Analysis (PCA). The Index score was calculated as the sum of the variables weighted by the loading obtained in the final PCA. Finally, the Cronbach's alpha test was used to measure the internal consistency and reliability of the index. The present investigation demonstrated that measuring only 9 traits (breast malondialdehyde, breast yield and live weight, allo-grooming, resting and running behaviours, n-6 polyunsaturated fatty acids (PUFA), and saturated fatty acids (SFA) of drumstick, blood PUFA, Heterophile/Lymphocyte ratio) of different pillars could be an efficient, rapid, and economical strategy to assess the adaptability of a chicken genotypes to ERS. The final classification showed that CB and LD genotypes had the worst indices, whereas NN and RJ showed the best ones. However, it is necessary verify the reliability of the present approach in different rearing conditions and with other genetic strains.