Specificities of the Local Kids Genotypes Expression Towards Arid Conditions in Southern Tunisia
About 5000 kids weights registered during four years in 9 herds raised in the Tunisian arid area were used in the aim to identify some genetic specificities of the local population productive behaviour towards harsh conditions. The analysis of kids growth under arid regions conditions shows a particular aspect of the genotypes expression in arid environment. The nature of the non-genetic factor effects on kids phenotypes distribution and parameters reveals a direct impact on the application of quantitative genetic methodologies for animal improvement. The expression of the "best" genetic potentialities seams to be limited by a maximum level defined by environmental factors. The normal distribution of kidís performances is not verified, especially in dry years, where the right tail of the bell curve disappeared. The statistical importance of certain parameters such as the means and the variance is modified. The construction of the mixed model could, in this special case, induce a bias or increase the variance of the prediction error. These considerations impose a revision of hypotheses and methodologies of the quantitative genetics for the livestock improvement in arid regions.