Abstract. The study of candidate genes, based on physiological effects, is an important tool to identify genes to
be used in marker-assisted selection programs. In this study, a group of halothane gene-free, non-castrated, male
Landrace pigs was used to study the association between polymorphisms in the PIT1 (n = 218), GH (n = 213) and
GHRH (n = 206) genes and fat thickness, average daily gain, and the EPD (expected progeny difference) for fat
thickness, average daily gain, and litter size. These genes are potential candidate markers because of their important
physiological effects. The pigs were genotyped by PCR-RFLP, and the statistical model used to analyze
the association between genotypes and the traits measured included genotypes as a fixed effect and age and
weight as covariates. PIT1 polymorphisms were associated with fat thickness (P = 0.0019), EPD for average
daily gain (P = 0.0001) and EPD for fat thickness (P = 0.0001), whereasGHpolymorphisms were associated with
fat thickness (P = 0.0326) and average daily gain (P = 0.0127), and GHRH polymorphisms were associated with
the average daily gain (P = 0.0001) and EPD for fat thickness (P = 0.0004). These results confirmed the potential
usefulness of these genes in marker-assisted selection programs for pig breeding.