Different penalty methods for assessing interval from first to successful insemination in Japanese Black heifers

The objective of this study was to determine the best approach for handling missing records of first to successful insemination (FS) in Japanese Black heifers.

Of a total of 2367 records used, 206 (8.7%) of open heifers were missing. Four penalty methods based on the number of inseminations were set as follows: C1 (FS average according to the number of inseminations), C2 (constant number of days; 359), C3 (maximum number of FS days to each insemination) and C4 (average of FS at the last insemination and FS of C2). C5 was generated by adding a constant number (21d) to the highest number of FS days in each contemporary group. The bootstrap method was used to compare among the 5 methods in terms of bias, mean squared error (MSE) and coefficient of correlation between estimated breeding value (EBV) of non-censored data and censored data. Three percentages (5%, 10% and 15%) were investigated using the random censoring scheme. The univariate animal model was used to conduct genetic analysis.

Heritability of FS in non-censored data was 0.012±0.016, slightly lower than the average estimate from the five penalty methods. C1, C2, and C3 showed lower standard errors of estimated heritability but demonstrated inconsistent results for different percentages of missing records. C4 showed moderate standard errors but more stable ones for all percentages of the missing records, whereas C5 showed the highest standard errors compared with noncensored data. The MSE in C4 heritability was 0.633×10–4, 0.879×10–4, 0.876×10–4 and 0.866 ×10–4 for 5%, 8.7%, 10%, and 15%, respectively, of the missing records. Thus, C4 showed the lowest and the most stable MSE of heritability; the coefficient of correlation for EBV was 0.88; 0.93 and 0.90 for heifer, sire and dam, respectively

C4 demonstrated the highest positive correlation with the non-censored data set and was consistent within different percentages of the missing records. We concluded that C4 was the best penalty method for missing records due to the stable value of estimated parameters and the highest coefficient of correlation.