If you own a female pig, knowing how to figure out when she's in estrus can be handy for anticipating her readiness for mating activities. Female cats, dogs and horses all often make it clear when they're in estrus, and swine are generally no different in these situations.
When a male pig -- or boar -- places pressure on a female's rear, the position she takes on generally signifies whether she's in estrus. If her body suddenly becomes stiff and motionless as she stands, then there's a strong chance that she's in estrus -- and therefore prepared to mate with the boar. This position is known as lordosis reflex. Female pigs in this position generally exhibit noticeably curved backs and fully upright ears.
Desire for Proximity to Boars
Female pigs in estrus generally go out of their way to be around boars, even more than usual. If you notice a boost in this behavior in your pig, it often means that she's started heat -- or is right about to start it, at least.
A female pig's vulva also can provide clues regarding estrus status. If a vulva is red and puffy, estrus is likely the cause. Red, puffy vulvae are particularly prominent in gilts, or young female pigs that haven't given birth before. Mature female pigs that have produced offspring before are sows. You also might notice a light, transparent and gooey substance coming out of your pig's vulva -- an effect of rising estrogen. These signs typically emerge anywhere between two and three days prior to the beginning of estrus.
Female pigs frequently exhibit a variety of behavioral clues when they're in estrus -- clues that are often more subtle than looking for boars. They sometimes become persistently vocal, making lots of low and smooth guttural noises. They also often lose some interest in eating their food. Some female pigs in estrus simply become more vigilant and attentive in overall behavior. They also sometimes behave in overly antsy manners, such as nonstop circling. Female pigs in heat occasionally try to get on top of other female pigs in season, too.
Estrus Time Span
Estrus in youthful gilts generally takes around two days, maximum. The typical estrus time span is a little longer in more experienced sows, however -- think 60 hours or so.
- Penn Veterinary Medicine: Estrus in Swine
- Pork Information Gateway Factsheet: Estrus or Heat Detection
- Iowa State University Iowa Pork Industry Center: Estrus
- University of Kentucky Cooperative Extension Service: Manipulation of the Estrous Cycle in Swine
- University of Illinois at Urbana-Champaign ACES: Managing Swine Reproduction
- University of Wisconsin-Madison Department of Animal Sciences: Estrus Detection
- Penn Veterinary Medicine: Estrus Detection in Swine
- Domestic Animal Behavior for Veterinarians and Animal Scientists; Katherine A. Houpt
- Purdue University Extension: Estrus Detection in Farm Animals