Sows not showing signs of estrus can be a major concern in pig farming. After weaning, the majority of sows should be monitored to determine if they are entering estrus. By comparing weaning-to-mating intervals with historical data, farmers can identify potential issues. Ideally, this interval should be less than 10 days, preferably 7 days or fewer. If the interval is too long, it delays farrowing and reduces the annual number of pigs per sow. A common cause is the "lean sow syndrome," often linked to poor nutrition during lactation in young sows. Checking the parity distribution can help identify whether the issue lies within the younger sow population. It's important not to assume that poor breeding performance is due to infectious diseases; antibiotics may not be the solution. Post-weaning estrus problems are typically related to management rather than disease.
Observing the sow’s vulva for redness, swelling, and mucus discharge is essential, but inexperienced staff may miss subtle 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. High temperatures can delay estrus after weaning, as heat stress reduces appetite and nutrient intake, contributing to lean sow syndrome. Keeping sows near boars or providing them with proper feeding can stimulate estrus.
Boar-related issues also affect breeding success. Poor management during development can lead to low libido in boars. Young boars may experience temporary sexual impotence during their first mating, but this usually resolves over time. Heat stress, foot problems, arthritis, or injuries can all reduce a boar’s mating ability. Severely affected boars should be culled to maintain productivity.
When sows show estrus after mating, it often indicates pregnancy failure. The normal return-to-breeding rate is below 15%, and a higher rate extends the farrowing interval and lowers the number of pigs per sow annually. Sows that fail to maintain pregnancy within 18–24 days post-mating may have had early miscarriages. Delayed breeding is a key factor in low pregnancy rates. The best time to breed is 21–22 hours after the onset of estrus. In large farms, daily observation and single breeding sessions may result in lower pregnancy rates. Breeding twice at 4–12 hour intervals significantly improves pregnancy rates and litter size.
Boar usage also impacts breeding success. Overuse can reduce semen quality, especially in young boars. However, using boars up to four times a week is generally safe. Infectious diseases like Porcine Reproductive and Respiratory Syndrome (PRRS), Parvovirus, and Brucellosis can cause high return rates.
Empty sows—those that appear pregnant but do not deliver—are another challenge. This can happen due to misdiagnosis or lack of proper estrus detection. Empty rates are usually around 5%, but can rise due to poor detection or infectious diseases. Inaccurate pregnancy diagnosis can inflate or deflate the true pregnancy rate. For example, a 90% pregnancy rate with only an 80% farrowing rate suggests possible issues in diagnosis or early abortions. PRRS can cause both high empty rates and low birth rates. Proper management and accurate monitoring are crucial to maintaining reproductive efficiency.
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