Mortality and Survival Probability of Breeding-Female Pigs in Southern European Commercial Herds

Decreasing the mortality risk in breeding-female pigs is critical to enhance maternal health and animal welfare in commercial herds, and it also helps prevent decreased productivity, economic losses and reduced worker morale. The objectives of the present study were to characterize death occurrences in female pigs, to examine the survival probability for gilts and sows in commercial herds, and to quantify factors associated with by-parity mortality risks for farrowed sows. The data included 558,486 first service records of 113,517 females in 121 herds, served between 2008 and 2013. Two herd categories were defined on the basis of the lower 25^th percentiles of the herd means of annualized lifetime pigs weaned per sow: low-performing herds (< 21.7 pigs) and ordinary herds (> 21.7 pigs). By-parity annualized mortality incidence rates for pregnant pigs and farrowed sows were calculated by using pig days as the denominator. Two-level survival analysis was performed for served female pigs to obtain by-parity survival probabilities. Also, log-binomial regression models were used to examine risk factors and risk ratios associated with by-parity mortality risks for farrowed sows. The mortality rate of the 113,517 removed females was 14.4%, with overall mean annualized mortality incidence rates (%) of 4.5 and 19.3% for pregnant female pigs and farrowed sows, respectively. Survival probabilities for served females rapidly decreased at around farrowing in all parity groups. Also, lower survival probabilities for served female pigs were associated with increased age at first-mating, females fed in low-performing herds, females that farrowed more stillborn piglets and females having WMI of 7 days or higher (P < 0.05). Increased mortality risks for farrowed sows were associated with summer farrowing, being fed in low-performing herds and having more stillborn piglets (P < 0.05). The relative risk ratios of parity 1 to parity 5 farrowed sows dying were 1.33-1.59 if they were being fed in low-performing herds, compared to those being fed in ordinary herds. Also, the relative risk ratios of sows that farrowed stillborn piglets dying were 1.56-2.67 across parity, compared to sows that had not farrowed stillborn piglets. However, herd size was not associated with mortality risk (P > 0.88). In conclusion, in order to prevent female pig death occurrences, producers need to provide more care and attention to female groups at high risk of dying, such as females in peripartum periods, pregnant gilts in late gestation, sows farrowing in summer and those being fed in low-performing herds.