Incidences and risk factors for prolapse removal in Spanish sow herds.

Prolapses in sows are an emerging concern in pig production. The objectives of this study were to estimate the incidence rate of prolapses and to determine risk factors associated with prolapse occurrences. Data included 905,089 service records in 819,754 parity records of 155,238 sows from 144 swine herds in Spain. Producers were required to record a removal reason, including type of prolapse. A 1:4 matched case-control study was carried out to investigate prolapse risk factors, and piecewise exponential models were applied to the data. The following factors were assessed: parity, number of services, service season, weeks after service, prior gestational length, total number of piglets born, and number of stillborn and mummified piglets. Almost 1% of sows (0.8%) were removed due to prolapses (95% confidence interval: 0.76, 0.85), and the annualized incidence rate for all prolapse cases was 3.8 cases per 1000 sow-years (95% confidence interval: 3.59, 4.01). Significant factors were the 16th week after service, being in parity 3 or higher, re-service, servicing in summer, autumn or winter, shorter gestational length, fewer piglets born and more stillborn piglets (P ≤  0.04). For example, the prolapse incidence was 30.6 times higher at 16 weeks after service than during the first 14 weeks (P <  0.01). Also, 60.9% of 1198 prolapses occurred during the first 0 to 4 weeks after farrowing. The prolapse incidence was 1.5-1.8 times higher in parity 3 or higher sows than in parity 0 sows (P <  0.01), and 1.3 times higher in re-serviced sows than in first serviced sows (P =  0.02). It was also 1.3-1.5 times higher in sows serviced in summer, autumn or winter than in those serviced in spring (P ≤  0.02), and 1.3-1.5 times higher in sows with a prior gestational length of 113 days or less than in sows with 114 days or more gestational length (P <  0.01). Lastly, the prolapse incidence rate was 1.2 times higher in sows with 11 or fewer piglets born than in sows with 12-16 piglets born (P =  0.04), and was also 1.4 times higher in sows with two or more stillborn piglets than in sows with no stillborn piglets (P <  0.01). However, there was no association between prolapse incidence and mummified piglets (P =  0.54). Consequently, producers should pay more attention to sows exposed to high risks, while trying to identify prolapse cases at an early stage.