Analysis of longevity and exterior traits on Large White sows in Switzerland1

Abstract

Records of length of productive life, from first farrowing to culling, of 16,464 Large White purebred sows from SUISAG were studied using survival analysis. The major aims of the study were to model the risk of culling within parity and to assess the influence of exterior traits, such as the number of teats or feet and leg scores, on culling. Culling was concentrated at the first day after each farrowing or at the first day after weaning. Weaning itself was mostly between 21 and 49 d after farrowing, with an average weaning age of 35 d. Because of the definition of culling date used, there was practically no risk of culling from these periods. The culling rates at different periods suggested a modeling of the baseline hazard function within parity instead of over the entire productive life of the animals. A piecewise Weibull function and a simple graphical method to validate its adequacy were proposed for sow longevity analysis. The risk of culling increased with older parities (P < 0.001) and with decreasing litter size at weaning (P < 0.001). The exterior traits analyzed (number of teats, and feet and leg scores, on a scale from 1 to 7) had a moderate effect on the risk of culling compared with other factors but were still influential on survival, productive life expectancy, and annual replacement rate. Sows with less than 13 good teats had 1.35 times greater risk of being culled than sows with more good teats (P < 0.05). Sows with an X-O rear leg score of 2 had 1.4 times greater risk of being culled than sows with an intermediate score of 4 (P < 0.05). Sows at the optimum score of 4 for the size of inner claws of the rear leg had 0.83 times less risk of being culled (P < 0.01) than sows with scores of 2 and 3. Furthermore, when a phenotypic index for feet and legs was used to group these variables, the effect was highly significant (P < 0.001). Therefore, a means to improve longevity is through phenotypic selection of replacement gilts based on exterior traits: gilts with 13 or less good teats or with extreme feet and leg scores should be culled. From a genetic point of view, sows with the best value in the current index for exterior traits had a lower risk of culling (P < 0.01), and therefore, it is possible to obtain a response for sow longevity via indirect selection for exterior traits. From 1999 to 2003, the trend has been to eliminate extreme animals on exterior traits. This may partly explain the improvement of sow length of productive life longevity from 560 d in 2000 to nearly 710 d in 2003 observed in the data set.

Competing risk analyses of longevity in Duroc sows with a special emphasis on leg conformation

“…This peculiarity led to high censoring percentages when competing risk analyses were performed. More specifically, censoring percentage ranged between 81.09% (LP) and 93.19% (DE), these values being clearly higher than the censoring percentages reported in other studies that focused on sow longevity (Tarré s et al, 2006a and2006b) although similar (Casellas et al, 2004(Casellas et al, and 2007 or smaller (Tarré s et al, 2005) than the ones obtained in young pigs or other species. Note that the analytical power of survival analysis substantially depends on censoring percentage (Vukasinovic et al, 1999;Yazdi et al, 2002).…”

“…As was expected, sow survival increased with the number of piglets born alive in the LP competing risk analysis, given its close relation to the number of weaned piglets. Note that litter size-related factors were revealed as one of the most important sources of variation influencing sow longevity in previous studies (Friendship et al, 1996;Yazdi et al, 2000a;Tarré s et al, 2006a). Sows with backfat thickness of more than 19 mm at the end of the growing period showed a higher risk of culling due to LP.…”

“…For each cause-specific analysis, four time-independent effects were included in the preliminary model: year at the first farrowing (2005 or 2006), farm of origin, backfat thickness at 6 months of age (categorized with cut-off points at 16 and 19 mm, following in part (Tarré s et al, 2006a)) and the linear and quadratic effects of age at first farrowing. Preliminary models also included three timedependent effects: the number of piglets born alive, and teat and leg-conformation scores modeled as time-dependent covariates that could change at the first two parities.…”

“…These results highlighted the underlying link between leg conformation and both sow productivity and fertility and their influence on sow survivability. It is important to note that leg-conformation scores and specific leg defects did not influence sow survival under the DE-specific competing risk analysis, although the overall influence of leg conformation on sow longevity is well established in the literature (Lopez-Serrano et al, 2000;Serenius and Stalder, 2004;Tarré s et al, 2006a;Fernà ndez Competing risk analyses in Duroc sows de Sevilla et al, 2008). It should also be considered that mobility problems would make it more difficult for sows to access resources as well as show a sow's normal behavior under the European Union directive 2001/88/EC (mandatory on European farms from January 1, 2013), which requires farmers to keep sows in group housing, from the 4th week of pregnancy until 1 week before farrowing.…”

Multivariate survival mixed models for genetic analysis of longevity traits

“…Longevity is an important trait often considered in animal breeding programs [31,30,33,37,27,35,17,9,6,32,1]. Even small changes in the longevity of a population under production might have remarkable economic, welfare and ethics consequences [30,12].…”