Effect of index selection for reduced backfat thickness and increased growth rate on sow weight changes through two parities in swine McKay, R. M. 1992. Effect of index selection for reduced backfat thickness and increased growth rate on sow weight changes through two parities in swine. Can. J. Anim. . The impact of continued selection for reduced backfat thickness and improved growth rate on weight changes in Yorkshire and Hampshire sows, from breeding as giits to weaning their second litter, was studied.Results suggest that some sow weight changes may have been influenced by selection pressure exerted.Key words: Sows, Canadian Yorkshire, Hampshire, liveweight change McKay, R. M. 1992. Effet de la s6lection pour la r6duction de l'dpaisseur du lard dorsal et pour I'augmentation du taux de croissance sur les modifications du poids des truies jusqu'ir la deuxibme mise bas. Can. J. Anim. . L'auteur a 6tudi6 I'effet d'une s6lection pour la r6duction de l'6paisseur du lard dorsal et pour I'am6lioration du taux de gain sur les modifications du poids des truies Yorkshire et Hampshire )r partir de leur premidre mise ir la reproduction jusqu'au sevrage de leur seconde port6e. Les r6sultats obtenus indiquent que certaines modifications de poids pourraient avoir 6t6 influenc6es par la pression de sdlection exercde. In either breed, there were only two sow weight changes that exhibited conclusive differences between the select and control lines. Though the presence of these differences does not prove conclusively that there was an effect due to the selection practised they also do not prove that selection had no effect. o-E--