Comparison of Methods for Handling Censored Records in Beef Fertility Data: Field Data

Abstract

The purpose of this study was to compare methods for handling censored days to calving records in beef cattle data, and verify results of an earlier simulation study. Data were records from naturalservice matings of 33,176 first-calf females in Australian Angus herds.Three methods for handling censored records were evaluated. Censored records (records on noncalving females) were assigned penalty values on a within-contemporary group basis under the first method (DCPEN). Under the second method (DCSIM), censored records were drawn from their respective predictive truncated normal distributions, whereas censored records were deleted under the third method (DCMISS). Data were analyzed using a mixed linear model that included the fixed effects of contemporary group and sex of calf, linear and quadratic covariates for age at mating, and random effects of animal andresidual error. A Bayesian approach via Gibbs sampling was used to estimate variance components and predict breeding values.Posterior means (PM) (SD) of additive genetic variance for DCPEN, DCSIM, and DCMISS were 22.6d² (4.2d²), 26.1d²(3.6d²), and 13.5d²(2.9d²),respectively. The PM (SD) of residual variance forDCPEN, DCSIM, and DCMISS were 431.4d²(5.0d²),371.4d² (4.5d²), and 262.2d²(3.4d²), respectively. ThePM (SD) of heritability for DCPEN, DCSIM, andDCMISS were 0.05 (0.01), 0.07 (0.01), and 0.05 (0.01),respectively. Simulating trait records for noncalvingfemales resulted in similar heritability to the penaltymethod but lower residual variance. Pearson correlationsbetween posterior means of animal effects for sireswith more than 20 daughters with records were 0.99between DCPEN and DCSIM, 0.77 between DCPENand DCMISS, and 0.81 between DCSIM and DCMISS.Of the 424 sires ranked in the top 10% and bottom 10%of sires in DCPEN, 91% and 89%, respectively, werealso ranked in the top 10% and bottom 10% in DCSIM.Little difference was observed between DCPEN andDCSIM for correlations between posterior means of animaleffects for sires, indicating that no major rerankingof sires would be expected. This finding suggests littledifference between these two censored data handlingtechniques for use in genetic evaluation of days to calving.