Altrenogest is an orally active progesterone-like compound that can be used to effectively synchronize estrus in cyclic gilts. In sows, progestagen treatment can aid in maximizing farrowing crate utilization by reducing the variation in services per week, increasing the number of pigs weaned per week, reducing variation in weekly weaned pig output and increasing overall breeding herd productivity. A negative energy balance in primiparous sows at weaning is often associated with extended weaning-to-estrus intervals and the syndrome known as the ‘second parity dip’ in sow fertility. Feeding progestagen to weaned sows essentially extends the weaning-to-service interval and allows the sows additional time to recover after weaning. This has been shown to improve the percentage of sows in estrus within 7 days of withdrawal, increase ovulation rate and/or embryo survival, and litter size (Kemp et al., 2006. University of Alberta/University of Minnesota Leman Pre-Conference Reproduction Workshop). The duration of progestagen treatment after weaning needed to produce optimal sow productivity is still unclear. Periods of 3 to 5 days after weaning are traditionally used in batch-farrowing systems (Martinat-Botté et al. 1995. Journees de la recherche porcine en France 27:51-56). However, changing physiology of the weaned sow (Kemp et al., 2006) suggests that longer periods of progestagen treatment may produce results more analogous to the response to ‘skip-a-heat’ breeding. In this experiment groups of multiparous sows (n = 749) weaned in two consecutive three-week periods in June and July were organized into two breeding weeks using the following strategies: M0 (n = 250): Wean weeks 3 and 6 (no progestagen treatment); M7 (n = 250): Wean weeks 2 and 4 (progestagen treatment for two days before and five days after weaning.); and M14 (n = 249): Wean weeks 1 and 3 (progestagen for two days before and 12 days after weaning). The results suggest that feeding progestagen was effective in delaying and synchronizing the return to estrus in weaned sows, and the duration of the treatment affected subsequent sow productivity. Sows treated with progestagen for 12 days after weaning produced the highest percentage of sows bred within 10 days of progestagen withdrawal and pregnant at day 50 of gestation. Also, feeding progestagen resulted in an increase in the number of fetuses at day 50 of gestation similar to that seen in previous ‘skip-a-heat’ studies. These results suggest that a longer progestagen treatment period than the five days typically used in batch-farrowing systems, would be likely to produce the same benefits to sow productivity as seen in response to ‘skip-a-heat’ breeding.