Genetic study of longevity in Swedish Landrace sows

Genetic parameters for length of productive life of Swedish Landrace sows were estimated using a proportional hazards model based on the Weibull distribution. Data were obtained from 7967 sows with at least one farrowing recorded, using the Swedish litter-recording scheme, from 1986 through 1998 from nucleus and multiplier herds. Effects of litter size at first and last farrowing, age at first farrowing, daily gain from birth to performance test (similar to 170 days of age), weight, and side-fat thickness at performance test were included in the model as fixed and time-independent explanatory variables. The effect of herd X year (of birth) combinations was treated differently in several analyses (random versus fixed and time-independent versus time-dependent). The random effect of sires, incorporating full pedigree information, was taken into account in all analyses as the source of genetic variation (sire model). The length of productive lifetime (longevity) of sows was the dependent variable and was defined as the number of days from first farrowing until culling. The suitability of the Weibull model was assessed by evaluating the log-cumulative hazard versus the log of longevity (in days), which indicated that the Weibull model could be fitted to the data satisfactorily. All explanatory factors except daily gain and side-fat had a significant effect on longevity of sows in all analyses. The effect of herd x year had the largest influence among the factors included. Among the various analyses, estimates of heritability for longevity ranged from 0.109 to 0.268 on the original scale. The estimates were similar within each group of models, averaging 0.13 for the time-independent and 0.25 for the time-dependent herd X year effect in the model. Correlations between sires' breeding value estimates were 0.98 between time-independent models and ranged from 0.96 to 0.98 among time-dependent models. It was concluded that there is genetic variation that can be utilised for increasing longevity by selection. (C) 2000 Elsevier Science B.V. All rights reserved.