Determining when a female pig (sow or gilt) is ready to be bred is fundamental to successful swine production. This reproductive phase is called estrus, or “heat,” and is the period when the pig is receptive to the boar and ovulation occurs. Detecting this time frame ensures efficient resource use and maximizes the likelihood of conception.
Observable Physical Indicators
The initial indication of heat involves changes in the external reproductive anatomy. The vulva typically becomes swollen and reddened due to increased blood flow. This transformation is often more pronounced in gilts than in mature sows.
A clear, watery, or sometimes slightly cloudy mucus discharge may also be present around the vulva. While swelling and color change are preliminary signs, they do not confirm readiness for breeding. Recognizing these early physical signs requires closer daily monitoring.
Recognizing Behavioral Changes
As the hormonal surge continues, the pig’s behavior shifts significantly, providing stronger evidence of estrus. Common changes include increased restlessness and agitation, often manifesting as pacing or an inability to settle down. This shift often coincides with increased vocalization, such as frequent, low-pitched grunting.
The pig’s daily routine is often disrupted, with many showing a decrease in appetite during the peak of the heat cycle. Pigs in heat interact differently with pen mates, demonstrating interest in mounting other females. They may also readily accept being mounted by other pigs, a behavior known as the “riding test.”
A particularly telling sign is the frequent attempt to urinate, resulting in small, short streams of urine. These behavioral cues serve as reliable precursors to the definitive test for breeding readiness.
Timing and the Immobility Test
The estrous cycle in pigs averages 18 to 24 days, with 21 days being the most common interval. The period when the pig is fully receptive to the boar, known as standing heat, generally lasts between 48 and 72 hours. Pinpointing the optimal window within this standing heat is necessary for successful conception.
The definitive method for confirming breeding readiness is the immobility test, also called the Standing Reflex. This test relies on the pig’s instinct to stand rigidly still when pressure is applied to her back, simulating the weight of a boar. The test is most effective when performed near a mature boar, whose pheromones and vocalizations help induce the reflex.
To perform the test, firm pressure should be applied to the pig’s loin area, either by hand or by sitting lightly on her back. A positive reaction is confirmed if the pig locks her legs, arches her back slightly, and remains motionless and rigid. This standing response indicates the pig is experiencing peak estrus and is prepared for mating.
For maximum conception rates, the pig should be bred shortly after the onset of the standing reflex. Since ovulation occurs in the latter half of standing heat, a common practice is to breed the pig once every 12 to 24 hours for the duration of the immobility response. This strategic timing ensures viable sperm are present when the eggs are released.