Factors affecting measures of longevity and stayability in Yorkshire sows

Adult sow lifetime is recognized as both an economic and welfare concern. However, there are not consistent definitions of sow longevity. The purpose of this study was to assess the relationship of developmental performance factors with longevity and to determine the genetic variation within six different descriptions of longevity. Longevity definitions included stayability (probability of producing 40 pigs or reaching four parities), lifespan (number of parities accumulated before culling), lifetime prolificacy (number of pigs born alive during a female's lifetime), herdlife (time from first farrowing to culling), and productive life (pigs produced per day of life).The edited data consisted of 14,262 records from Yorkshire females with at least one farrowing record, from both nucleus and multiplication herds across 21 farms. Within a subset of the data, information was available on the female's litter birth record and corresponding growth and composition data. Furthermore, complete pedigrees were available on 7,487 females. The data were subdivided into two data sets Data A: female's farrowing records, and Data B: Data A and the information from a female's litter birth record and her growth and backfat data. Due to a reduced number of records with complete pedigree information, two separate analyses were completed.Initially, a Cox proportional hazards model was used to determine the relationship of developmental factors and first farrowing record with longevity. Those factors that were significantly (P <0.0001) associated with longevity, regardless of definition, were age at first farrowing, litter size at first farrowing and last farrowing, number of stillborn in her first lifter, adjusted 21 day litter weight of first lifter, herd type (nucleus or multiplier), and standardized variables for backfat and growth. Within a contemporary group, fatter, slower growing gilts had a decreased risk of being culled. Additionally, sows that had more pigs born olive, fewer stillborn, and heavier litters at weaning in their first lifter had a decreased risk of being culled. Furthermore, sows from nucleus herds experienced a greater risk of being culled.Heritability was estimated for four different descriptions of longevity (lifespan, lifetime prolificacy, herdlife, and pigs produced per day of life) with survival analysis by using a proportional hazards model with an underlying Weibull distribution. A threshold model was used to estimate heritability for two descriptions of stayability on a subset of the original data (n=5,889) that did not include censored observations. Fixed effects within the two model types were similar to those reported previously. Random effects were sire and the interaction of herd by year. Fixed effects were consistent in their significance, regardless of statistical model or definition. Heritability estimates ranged from 0.039 to 0.050 and from 0.076 to 0.231 for true and functional definitions of survival analyses, respectively and from 0.117 to 0.200 for threshold analyses.Results indicated that there are early indicators that can be monitored to provide insight to the future productivity or length of productive life of Yorkshire females. Additionally, sufficient genetic variation exists, regardless of definition, to improve sow longevity. Pork producers can implement management protocols which can extend the productive life of breeding females resulting in improved profitability and animal welfare.