Analyse d'une expérience de sélection divergente pour le poids total de la toison chez le lapin angora

Abstract

In this thesis, we present our research to analyze the efficiency of an experiment of divergent selection in French Angora rabbit. Objectives of the experiment were a) to assess genetic parameter estimatesfor total fleece weight and correlated trait and b) to get an experience on management of a population of angora rabbits under selection with overlapping generations. This thesis is also the last research project of INRA after nearly 30 years of research on this animal. We present an overview of the genetic and non-genetic factors of quantitative and qualitative traits influencing fibre production. Among fixed effects, number of harvest was the most important. The genetic parameters and genetic trends were analysed using a BLUP animal model. For estimation of genetics parameters the repeatability model was used in which wool harvests from third until 12th have been considered as a repeated trait. Results showed that selection for high and low total fleece weight was successfully performed and a divergence of three genetic standard deviations was observed between the high and low lines after eight years of selection. Selection for total fleece weight significantly increased bristle length, secondary to primary follicle ratio and comfort factor and decreased compression, resilience, bristle diameter, and average fibre diameter. These changes resulted from moderate to high genetic correlations between total fleece weight and bristle length, and between fibre dimensions and secondary to primary follicle ratio, comfort factor, compression and resilience. Thus, selection for increasing total fleece weight results in an increase of both quantitative and qualitative traits of wool production in the French Angora rabbit. Measurement of total fleece weight is simple and easy at the farm level. Selection for this trait has positiveeffects on fleece characteristics such as bristle length, follicle population and fibre diameter. This thesis also contains new genetic parameters Angora fibres resulting from measurements by Optical Fibre Diameter Analyser that we provide a rapid method for measuring the characteristics of Angora fibre. Some of these measurements are interesting because of having a high genetic correlation with follicle traits of skin. The OFDA methodology is an interesting alternative to evaluate important characteristics such as fibre diameter, CV of fibre diameter and bristle content through measuring of comfort factor. We describe the demography and genealogy of the studied population. In addition, we study differential of selection for total fleece weight and body weight. The main characteristic of our approach is the use of new method for description of differential of selection in candidates of selection, parent and theoretical parents. Description of demography and the genetic structure in this study showed that in the two divergent lines, the similar management of reproducers has been done successfully during 8 years of selection. Our work contributes to the research in two areas that are estimation of genetic parameters with multivariate models of best linear unbiased prediction of breeding value and theoretical investigation of selection in populations with overlapping generations. This thesis is also of practical interest for Angora rabbit breeders for knowledge of effects of selection for total fleece weight and correlated traitsTOULOUSE-ENSAT-Documentation (315552324) / SudocSudocFranceF