Sow longevity influences farm economy and can be considered an important indicator of animal welfare. Body features such as leg conformation can play a key role in sow longevity, although little is known about its effect on culling decisions. Within this context, longevity data from 587 Duroc, 239 Landrace, and 217 Large White sows were analyzed with special emphasis on the effect of leg conformation. Sow longevity was analyzed twice for each breed, testing the effect of a subjective overall score for leg conformation, or the presence or absence of 6 specific leg conformation defects. Each preliminary model also included a teat conformation score with 3 levels, farm or origin, backfat thickness at 6 mo of age, and 2 continuous sources of variation, namely the age at the first farrowing and the number of piglets born alive at each farrowing. Overall leg conformation score influenced (P < 0.01) sow longevity in Duroc, Landrace, and Large White sows, with a greater hazard ratio (HR) for poorly conformed sows (1.56, 2.16, and 1.79, respectively) than for well-conformed sows (0.32, 0.66, and 0.68, respectively). Abnormal hoof growth reduced survivability in Duroc (HR = 2.78; P < 0.001) and Landrace sows (HR = 1.88; P < 0.01); the presence of splayed feet (P < 0.05) or bumps and injuries (P < 0.001) increased the risk of culling in Duroc sows (HR = 2.08 and 3.57, respectively), whereas the incidence of straight pastern increased the HR in Large White sows (HR = 2.49; P < 0.01). In all 3 breeds, longevity decreased for plantigrade sows, with a greater HR in Duroc (HR = 3.38; P < 0.001) than in Landrace (HR = 1.53; P < 0.10) and Large White sows (HR = 1.73; P < 0.05). Teat conformation did not influence sow longevity (P > 0.10). Estimates of heritability for longevity in Duroc sows ranged from 0.05 to 0.07 depending on the algorithm applied. Leg conformation had a substantial effect on sow longevity, where an accurate removal of poorly leg-conformed candidate gilts before first mating could improve sow survival and reduce culling costs. These moderate estimates of heritability indicated that survivability of Duroc sows could be genetically improved by direct selection for leg conformation.

A Bayesian threshold animal model was applied to evaluate the prevalence over 2 farrowings and genetic background of overall leg conformation score and the presence or absence of 6 specific leg defects (abnormal hoof growth, splay footed, plantigradism, straight pasterns, sickle-hocked legs, and the presence of swelling or injuries) in purebred Landrace and Large White sows. Data sets contained phenotypic records from 2,477 and 1,550 Landrace and Large White females, respectively, at the end of the growing period. Leg conformation data from first and second farrowings were available for 223 and 191 Landrace sows and 213 and 193 Large White sows, respectively. Overall leg conformation deteriorated with age, with statistically relevant differences between females at the end of the growing period, first farrowing (FF), and second farrowing (SF). In a similar way, the prevalence of the 6 specific leg defects increased between the end of the growing period and FF (with the exception of straight pasterns in the Landrace population). Differences between FF and second farrowing were statistically relevant for hoof growth (highest posterior density regions at 95% did not overlap), plantigradism, sickle-hocked legs, and overall leg conformation score in Landrace and for sickle-hocked leg and overall leg conformation score in Large White. The statistical relevance of the genetic background was tested through the Bayes factor (BF) between the model with the additive genetic component and the model with 0 heritability (nonheritable). Heritability (h(2)) was discarded (BF < 1) for sickle-hocked leg in both breeds, whereas decisive evidence (BF > 100) of genetic background was obtained for overall leg conformation score in Landrace and Large White sows (h(2) = 0.27 and 0.38, respectively), hoof growth in both breeds (h(2) = 0.22 and 0.26, respectively), and plantigradism (h(2) = 0.34) and the presence of swelling or injuries in Landrace (h(2) = 0.27). Note that a BF > 100 implies that the model with infinitesimal genetic effects was more than 100 times more suitable than the model without genetic effects, a conclusive estimate within the Bayesian framework. The remaining traits (splay footed and straight pasterns) registered BF values ranging from 11.6 to 35.1 and h(2) values ranging from 0.09 to 0.19. These results indicated a moderate genetic determinism for leg conformation in Landrace and Large White sows.

No 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 , 0.05 for DE and P , 0.001 for LP and LF) whereas farm of origin accounted for relevant variation in the LP and LF analyses. LP culling increased with backfat thickness of more than 19 mm at the end of the growth period ( P , 0.05), bad teat condition ( P , 0.05) and reduced piglets born alive ( P , 0.001). For the LF competing risk analysis, culling increased with age at first farrowing ( P , 0.1). Special emphasis was placed on the influence of leg and teat conformation on sow survivability, although they did not affect sow failure due to DE ( 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 5 3.372 and 6.002, respectively; P , 0.001) and bumps or injuries to legs (HR 5 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.