Although never investigated, gonadotropin-releasing hormone II (GnRH-II) may be associated with the interaction between nutritional status and reproduction in swine. Therefore, we examined the role of GnRH-II in return to estrus following lactation of first parity sows. The objectives of our study were: 1) Determine GnRH-II levels between first parity sows fed a restricted or ad libitum lactation diet and 2) Do reproductive characteristics improve following GnRH-II treatment of first parity sows with a negative energy balance at weaning? In Objective 1, first parity sows (n = 17) were farrowed, weighed, and backfat thickness was determined by ultrasound. Standard farrowing traits were recorded including weights of corresponding piglets. After farrowing, litter sizes were standardized within treatment and sows were fed either an ad libitum or restricted (80% of ad libitum) standard lactation diet for 25 days. At weaning, sows were weighed, tenth rib backfat thickness was determined by ultrasound, and a blood sample was taken. Three sows from each treatment were sacrificed and tissue samples from the hypothalamus, anterior pituitary gland, ovaries, oviduct, uterus, fat and mammary glands were collected from each sow. The remaining sows in each treatment were exposed twice daily to boars for 15 days to determine wean-to-estrus interval and days in estrus. Blood samples were analyzed for GnRH-II concentrations and gene expression assays for GnRH-II were performed on each tissue sample. As expected, average daily feed intake was reduced in restricted compared to ad libitum fed sows. However, sow weight loss, sow backfat loss, litter weight gain, average piglet weight gain, wean-to-estrus interval and days in estrus did not differ between treatments. Although there were no differences between treatments for GnRH-II gene expression in any of the tissues collected, GnRH-II levels in the blood were significantly higher in restricted vs. ad libitum fed sows. In Objective 2, first parity sows (n = 30) were weighed and farrowed and standard farrowing traits as well as feed intake were recorded. At weaning, a blood sample was collected and sows were weighed and treated with either saline or a synthetic version of GnRH-II. Once daily boar exposure was provided for 15 days to determine wean-to-estrus interval. Next, blood samples were analyzed for GnRH-II concentrations. Unexpectedly, GnRH-II treatment had no effect on wean-to-estrus interval, exhibiting similar effects as saline. Therefore, we examined correlations between farrowing/weaning traits with GnRH-II levels in the blood at weaning. Interestingly, GnRH-II concentrations were negatively correlated with average daily feed intake and total feed consumed. Based on results from both studieswe were unable to link GnRH-II levels at weaning with subsequent return to estrus. However, we did find an exciting result, sows with reduced blood levels of GnRH-II at weaning ate more feed during lactation. Although further studies are warranted, GnRH-II concentrations measured in the blood may represent an early indicator (i.e., prior to lactation) of appetite issues in lactating sows. In addition, synthetic agents designed to reduce GnRH-II concentrations could be given to stimulate appetite in non-eating sows, enhancing sow productivity and therefore, profitability of pork producers. Dr. Brett R. White – phone: 402-472-6438; email: email@example.com.