PIT1, a member of the POU-domain family of genes, is a positive regulatoryfactor of growth hormone, prolactin, and thyrotroph-stimulating hormone beta inseveral mammals. Therefore, PIT1 was chosen as a candidate gene to investigateits association with growth and carcass traits in pigs. The five Iowa StateUniversity reference/resource three-generation families consisting of crosses ofMeishan x Duroc, Meishan x Hampshire, Meishan x Landrace, Minzhu x Hampshire,and Minzhu x Landrace were used. The three PIT1 polymorphisms were based on twoRFLP using a PIT1 POU-domain cDNA probe and the restriction enzymes BamHI andMspI and a PCR/RFLP using RsaI. Birth, 21-d, and 42-d weights, average dailygain, several backfat measurements, longissimus muscle area, muscle color,marbling, and firmness scores were evaluated for their association with thethree PIT1 polymorphisms. Mixed-animal-model analyses were used with theinformative family data in which the PIT1 polymorphisms were segregating.Results from mixed-model analyses revealed that pigs with the MspI CC genotype(P < .01) were associated with heavier birth weight (.12 kg) than DD genotypepigs. The MspI CC genotype pigs were also significantly associated with greateraverage backfat (.41 cm, P < .01), greater first-rib backfat (.45 cm, P < .01),greater last-rib backfat (.32 cm, P < .07), and greater last lumbar backfat (.46cm, P < .10) than the DD genotype pigs. The CC genotype represents primarilyChinese alleles and may be useful for future genetic improvement in syntheticlines involving Chinese and American pigs.(ABSTRACT TRUNCATED AT 250 WORDS)