Reasons for unsatisfactory breeding
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Sows do not show estrus. It is important for the majority of sows to avoid excessive investigation into the causes of estrus after weaning. Instead, farm managers should compare weaning-to-mating intervals with historical data. A normal weaning-to-mating interval should be less than 10 days, ideally under 7 days. If this interval is too long, it delays farrowing and reduces the number of pigs produced per sow annually. Common causes include the "thin sow syndrome," often due to poor nutrition during lactation in young sows. Checking the parity distribution can help identify if the issue lies within the younger sow group. Don’t assume that low breeding efficiency is always caused by infectious diseases—antibiotics may not be the solution. Post-weaning estrus issues are usually management-related, not disease-driven.
Observing the sow’s vulva for redness, swelling, and mucus discharge is key. However, inexperienced staff may miss these signs, leading to missed breeding opportunities. Morning and evening observations are most effective, as they increase the chances of detecting estrus and improving fertility rates. Heat stress can delay post-weaning estrus, as sows may lose appetite and fail to get enough nutrients, worsening the thin sow syndrome. Keeping sows and boars together or providing them with proper feeding can stimulate estrus.
Poor breeding performance in boars is often due to improper management. Young boars may initially show sexual inactivity, but this is usually temporary. High temperatures can reduce libido and mating behavior, especially on hot, humid afternoons. Conditions like foot dysplasia, arthritis, or leg injuries also affect their ability to mate. Boars that are permanently unable to breed should be culled.
Estrus after mating indicates a failure in pregnancy. A typical return-to-breeding rate is below 15%, but higher rates extend the farrowing interval and lower annual productivity. Sows that show estrus between 18–24 days post-mating may have had an early miscarriage. Delayed breeding is a major cause of low pregnancy rates. The best time to breed is 21–22 hours after the start of estrus. Observing once daily makes it hard to detect estrus accurately, as sows ovulate 24–36 hours after showing signs. In large farms, it's difficult to track each sow’s ovulation. Breeding once a day leads to low pregnancy rates, while two observations spaced 4–12 hours apart significantly improve both pregnancy and litter size.
Boar use also affects breeding success. Underused boars may have poor semen quality. Young boars (under two weeks) produce little sperm in their first ejaculation. Frequent use (up to four times per week) does not harm fertility. Infectious diseases such as Porcine Reproductive and Respiratory Syndrome (PRRS), Parvovirus, and Brucellosis can cause high return-to-breeding rates.
Empty sows are those that do not come into heat despite being pregnant. This can occur due to misdiagnosis or lack of accurate estrus detection. Empty rates are typically around 5%, but can rise due to poor detection or disease. Misidentification of pregnancy can lead to inflated pregnancy rates and higher empty rates. For example, a 90% pregnancy rate with only 80% farrowing rate suggests possible issues with diagnosis or early pregnancy loss. Diseases like Brucellosis can cause reproductive problems, as can PRRS, which is also linked to high return rates and low birth rates. Accurate estrus detection and regular health monitoring are essential to minimize empty sows and improve overall farm productivity.