7th World Congress on Genetics Applied to Livestock Production, August 19-23, 2002, Montpellier, France TRANSCORTIN : A STRONG POSITIONAL CANDIDATE FOR A QTL ASSOCIATED WITH CORTISOL LEVELS AND CARCASS COMPOSITION IN PIGS O. Ousova 1 , N. Iannuccelli 2 , D. Milan 2 , J. P. Bidanel 4 , C. Genêt 2 , M. Yerle 2 , J. Gellin 2 , P. Chardon 3 , P. Mormède 1 and M. P. Moisan 1 1 Laboratoire de Neurogénétique et Stress, INSERM U471-INRA UR502 Institut François Magendie, rue Camille Saint Saëns, 33077 Bordeaux, France 2 Laboratoire de Génétique Cellulaire, Centre de Recherche INRA de Toulouse-Auzeville, BP 27, 31326 Castanet Tolosan, France 3 Laboratoire d’Etude et de Recherche sur les Génomes, INRA, 78352 Jouy en Josas, France 4 Station de Génétique Quantitative et Appliquée, INRA, 78352 Jouy-en-Josas, France INTRODUCTION The Meishan pig breed has plasma cortisol concentration twice higher than control animals derived from Landrace (Mormède et al. 1984) and than the Large White breed (Désautés et al. 1999). In addition, the Meishan pigs are obese and display a reduced growth rate that may be a consequence of high cortisol levels. We searched for the genetic factors underlying these traits by QTL genetic mapping on F2 crosses between Meishan and Large White pig breeds (Bidanel et al. 2000). Here we report on the fine mapping of a QTL associated with cortisol levels, but also with carcass composition, and provide evidence suggesting that transcortin also called Corticosteroid binding globulin (Cbg) may be the causal gene. METHODS Genetic linkage analysis. Six hundred and twenty-six 6-week-old F2 piglets were exposed to a novel environment stress and blood samples were collected before and after the test. Plasma concentrations of cortisol were measured from these blood samples (Désautés et al. 1997). The same animals were genotyped with 137 markers covering the major part of the porcine genome. F2 males were slaughtered around 80 kg live weight and submitted to a standardised cutting of the carcass. Fifteen traits, i.e. dressing percentage, loin, ham, shoulder, belly, backfat, leaf fat feet and head weights, backfat thickness, muscle depth, ham + loin and back + leaf fat percentages and estimated carcass lean content were analysed. Genetic linkage analysis was performed for each chromosome using a multiple marker maximum likelihood procedure assuming a half sib family structure for F2 pigs (Le Roy et al. 1998). Radiation Hybrid mapping. Reactions were performed in independent duplicate on IMpRH panel (Yerle et al. 1998). PCR products were analyzed on 2% agarose gels in 1X TBE buffer after staining with ethidium bromide. A third amplification was carried out on clones for which discordant results were obtained. Vectors of amplification results were submitted to IMpRH database accessible at http://imprh.toulouse.inra.fr (Milan et al. 2000). CBG Binding assay. The binding capacity of CBG and its affinity for cortisol were measured at 4°C by a solid phase binding assay using Concanavalin A-Sepharose (Pugeat et al. 1984). The equilibrium association constant (Ka) and the capacity of CBG for cortisol were calculated Session 03. Pig breeding Communication N° 03-15