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Litter size plays a major role in the economics of swine production. Even modest increases in average litter size can have considerable effects on overall profitability. Two major components of litter size, 1) ovulation rate, and 2) embryonic survival, have been used in a selection index project ongoing for several generations at the University of Nebraska-Lincoln (UNL). To better understand the mechanisms of one component, ovulation rate, we are investigating the role of the gonadotropin-releasing hormone (GnRH) receptor in determination of this important trait. Although other factors may influence determination of ovulation rate, this receptor has an established physiological importance to the processes comprising ovulation rate, recruitment of follicles and regulation of ovulation. In addition, the GnRH receptor gene is located near a chromosomal marker for ovulation rate in the pig, providing a genetic rationale to study this receptor. Recently, the sequence for the porcine GnRH receptor gene has been determined, allowing comparisons between lines of pigs divergent for ovulation rate. Identification of unique genetic changes in swine strains with increased ovulation rates, such as the Chinese Meishan and the index selection line at UNL, may allow for a better understanding of prolificacy. This critical information may also be utilized to enhance litter size in other lines of pigs and improve efficiency of pig production.