Sow mortality has been a growing concern over the last decade. The average annual replacement rate is around 50%, with most removals occurring on parity-zero or parity one females before a positive net present value is achieved. Most studies assess mortality within a limited time frame of a couple of years.

A study led by Mariana Kikuti, University of Minnesota, investigated sow mortality over the course of nine years. The study was presented as a poster at the 2022 Leman Conference.

Historical production data from April 2009 to October 2018 (totaling 470 weeks) were obtained from four commercial farms from one production system located in the US Midwest region, representative of current production practices.

Deaths and culls were compared based on their lifetime contribution time (female life days between the first service to the removal date) and parity at removal. Deaths were described by removal reasons, by month, days from last service, days from last farrow, and parity at removal.

Risk factors associated with mortality were assessed using two different models: 1) a Poisson model to estimate factors associated with the number of deaths per week and 2) a multilevel Poisson regression to model the sow’s individual risk of dying throughout their lifetime.

The researchers obtained 357,425 service records of 85,608 sows. Of these, 70,467 were removed during the study period (11,852 died and 58,615 were culled). The average annualized mortality per month ranged from 1.79% to 3.29% for all farms combined.

Risk factors

Deaths occurred at a median of 116 days from last service, or 26 days post-partum. The median parity upon death was two. Overall, the main reasons for death were locomotion (27%) and reproduction (24%).

A higher weekly number of deaths was associated with spring and summer, incidence rate ratio (IRR) 1.27 and 1.37, respectively, compared to winter.

Sows had a higher mortality rate when they had been exposed to at least one PRRS break during their lifetime (IRR 1.55) and when housed in groups (pens) during gestation (IRR 1.32); and lower mortality rate when housed in filtered farms (IRR 0.76), accounting for an interaction between parity at removal and PRRS outbreak exposure.

The majority of the deaths occurred during the summer months. There was a greater probability of high mortality during warmer weeks, likely related to factors aggravating thermal stress.

Most deaths occurred at younger parities during peripartum, which hinders cost-competitiveness of the sow farms operations, noted the researchers.