Genetic study of longevity in Swedish Landrace sows

Genetic parameters for length of productive life of Swedish Landrace sows w ere estimated using a proportional hazards model based on the Weibull distr ibution. Data were obtained from 7967 sows with at least one farrowing reco rded, using the Swedish litter-recording scheme, from 1986 through 1998 fro m nucleus and multiplier herds. Effects of litter size at first and last fa rrowing, 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 di fferently in several analyses (random versus fixed and time-independent ver sus time-dependent). The random effect of sires, incorporating full pedigre e information, was taken into account in all analyses as the source of gene tic variation (sire model). The length of productive lifetime (longevity) o f sows was the dependent variable and was defined as the number of days fro m first farrowing until culling. The suitability of the Weibull model was a ssessed by evaluating the log-cumulative hazard versus the log of longevity (in days), which indicated that the Weibull model could be fitted to the d ata satisfactorily. All explanatory factors except daily gain and side-fat had a significant effect on longevity of sows in all analyses. The effect o f herd x year had the largest influence among the factors included. Among t he 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 t ime-dependent herd X year effect in the model. Correlations between sires' breeding value estimates were 0.98 between time-independent models and rang ed from 0.96 to 0.98 among time-dependent models. It was concluded that the re is genetic variation that can be utilised for increasing longevity by se lection. (C) 2000 Elsevier Science B.V. All rights reserved.