Evaluation of welfare in Italian poultry breeds based on genetic parameters

Over the last years, control of animal welfare has become a major issue and even a point of contention in aviculture together with the sustainable development of breeding. In fact, in highly intensive livestock farming animals not always express their natural behaviour and they get a stress that reduces the performances both qualitatively and quantitatively. Consequently, there is an increased need to define specific stress markers. The measurement of plasma corticosterone level is widespread in aviculture. Alterations in hypothalamus-pituitary-adrenal (HPA) axis secretion are associated with an altered animal welfare. However, because of the great number and variability of the stressors in avian breeding, other indicators should be also studied. Also the molecular genetics studies allow to evaluate the stress condition. Mainly in medical field has been pointed out the existence of strong genetic component in the stress predisposition. This is particularly true for the genotype of loci involved with the glucocorticoid hormones function. In human was observed that the regulation of the glucocorticoid receptor gene NR31C (Nuclear Receptor subfamily 3, group C, member 1) expression is involved in the control of depressive syndromes. The aim of the work was to study the response of three different Italian poultry breeds (Ancona, Livorno and Naked neck) to a number of stressors by taking into account genetic markers and, in particular, to define glucocorticoid receptor gene expression in these animals. At this purpose, 180 animals (1 day old) of the three breeds before mentioned (60 for each breed) were raised in stressful conditions: the stress agent was represented by the rearing density (15 heads/m2 or 30 kg/m2). In order to get an indicator of the level of stress suffered by animals, was determined the level of plasma corticosterone at the age of 40 and 80 days. At 81 days all the chickens were slaughtered and samples of liver were collected from each bird, immediately frozen in liquid nitrogen and stored at -80°C. From the samples of the liver, total RNA was extracted and utilized for the synthesis of the cDNA necessary for the reactions of real time PCR that quantify the absolute level of expression of the NR31C gene. The reaction was conducted using a pair of specific primers and TaqMan probe. The rate of corticosterolo in the blood was then correlated with the levels of NR31C expression. The study is in progress but this stress indicator, for its genetic derivation, can be considered suitable for a scheme of divergent selection in order to create chicken genetic lines well adapted to different breeding systems. Particularly, for intensive breeding, can be constituted genetic types characterized by a low level of corticosterone and high expression of GR, while, for plain-air rural production, can be useful genetic types with opposite characteristics.