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Description: This Hampshire boar is walked in front of the sows (left) to determine which sows are in heat. The boar hesitates in front of a sow that he detects by olfaction is in heat (estrus). With the boar in front, as a major sign of estrus, the sow then responds by arching her back in response to gentle pressure on her back. Typically, such sows are inseminated about 12 hours after first detected in estrus, and again daily until they no longer show estrus.