Animal (Jan 2009)
Competing risk analyses of longevity in Duroc sows with a special emphasis on leg conformation
Abstract
A competing risk approach was used to evaluate the influence of several factors on culling risk for 587 Duroc sows. Three different analyses were performed according to whether sow failure was due to death during productive life (DE) or to one of two causes for voluntary culling: low productivity (LP) and low fertility (LF). Sow survival was analyzed by the Cox model. Year at first farrowing (batch effect) significantly affected sow survival in all three analyses (P 0.1). The overall leg-conformation score significantly influenced sow longevity in LP (P < 0.001) and LF competing risk analyses (P < 0.001), showing a higher hazard ratio (HR) for poorly conformed sows (1.013 and 4.366, respectively) than for well-conformed sows (0.342 and 0.246, respectively). Survival decreased with the presence of abnormal hoof growth in LP and LF analyses (HR = 3.372 and 6.002, respectively; P < 0.001) and bumps or injuries to legs (HR = 4.172 and 5.839, respectively; P < 0.01). Plantigradism reduced sow survival in the LP analysis (P < 0.05), while sickle-hooked leg (P < 0.05) impaired sow survival in the fertility-specific analysis. Estimates of heritability for longevity related to LP culling ranged from 0.008 to 0.024 depending on the estimation procedure, whereas heritability values increased to between 0.017 and 0.083 in LF analysis. These analyses highlighted substantial discrepancies in the sources of variation and genetic background of sow longevity depending on the cause of failure. The estimated heritabilities suggested that direct genetic improvement for sow longevity seemed feasible, although only a small genetic progress was expected.
