In modern pork production, most sows are bred at their first heat (estrus) after weaning. However, some herds may benefit from allowing all first parity (P1) sows to rest for one estrous cycle (~21 days) before rebreeding, a practice commonly known as “skip-a-heat.” Research presented at the 2025 Al Leman Swine Conference in St. Paul, Minnesota, suggests that this strategy can improve second parity (P2) reproductive performance. According to Paul Thomas (AMVC), a field study demonstrated several advantages, including 0.7 to 1.2 more liveborn pigs in the second parity, a 3.5 percentage-point increase in farrowing rate, and 27.7 non-productive days (NPD) for rested sows compared with 13.2 days for sows bred immediately after weaning. No data are available regarding effects on parity structure.
The biological rationale for skipping a heat is straightforward. First parity sows typically experience the greatest body weight loss during lactation because their feed intake is often lower than that of older sows. Allowing these females an additional 21-day rest before rebreeding provides them the opportunity to regain body condition, which may be especially beneficial for sows that farrowed overweight or were lactating during the hot summer months. The extra recovery time may also improve uterine health, ovulation rate, sperm transport, embryo implantation, and placental development. Together, these factors could contribute to improved longevity and retention in the breeding herd, increasing the likelihood that a sow reaches her third parity, the point at which she is generally considered to have paid for her development costs.
Despite these potential benefits, several practical challenges should be considered. Resting P1 sows require approximately 28 days of feed compared with about 13 days when bred after weaning. Additional breeding pens or crates are needed to house these females during the resting period. Skipping a heat can reduce the number of farrowings in the group with which the sows were originally scheduled and may require the culling of additional older sows in the group they eventually join. Labor requirements, however, are expected to change little because management largely involves feeding and monitoring body condition for an extra three weeks
A short-term simulation (Table 1) assuming 100 weaned P1 sows per batch indicates that skipping the first post-weaning heat approximately doubles feed, housing, and labor costs compared with immediate breeding. Feed accounts for about 64% of the cost, labor for 22%, and housing and equipment for the remaining 14%. While increased litter size in the second parity helps offset these expenses, the financial margin remains relatively narrow.
Click here to see more...