The prolactin receptor gene was investigated as a candidate gene for reproduction traits in five PIC lines consisting of Large White (2), Landrace, Duroc, and Large White/Meishan origin. Least squares means for total number born (TNB) and number born alive (NBA) were calculated for each genotype in addition to an analysis of additive and dominance effects by line. The PRLR gene was significantly associated with TNB and/or NBA in three of the lines tested. The effect was greater than one pig for NBA in one line, although the effect clearly varied depending on the background genetics of the line. Additional data is needed to confirm the significant effects seen in these three lines. However, the effects observed to date suggest that this gene test has the potential to be a powerful tool when used in conjunction with traditional selection methods for some lines.