Data were compiled and analyzed to identify sows that are most likely to fail to express symptoms of estrus within 4–7 days after weaning. Five variables expected to influence estrus expression in sows were considered. Identification of those sows would allow producers to induce estrus by injection of gonadotropin hormone (PG600) at weaning. In that way reduction of nonproductive days is possible. Genetic line and parity had a significant effect on rebreeding rate in this study. Line C-15 females had significantly lower rebreeding rate when compared to C- 42 and C-22 females. A lower rebreeding rate for first parity females was observed. Administration of gonadotropins to females with a greater likelihood of a prolonged wean to estrus interval and lower rebreeding rate may help to improve reproductive performance of sows and decrease nonproductive days.