Abstract. The proportional hazards method was used to estimate breeding values for functional length of productive life within the endangered Slovak Pinzgau population. The analyzed data set contained 21,985 cows, daughters of 254 sires. The risk of culling was higher for cows with lower milk production relative to herd average, higher age at first calving and in herds decreasing in size. In the first lactation the culling risk was highest at the beginning, and decreased during lactation. From second lactation onwards an increasing risk was observed. The effect of breed composition was found insignificant, and was not included into final model. A heritability of 0.05 was estimated for functional length of productive life. The average reliability of estimates was 0.25. No clear tendency in average breeding values by year of birth of bulls was observed.
Abstract. Genetic evaluation of sires for functional longevity was conducted using survival analysis techniques. The data set consisted of 49 659 Simmental cows with first calving from 1997 to 2008. A piecewise Weibull sire model was used to estimate breeding values of 251 bulls for functional length of productive life of their daughters. The model was stratified by parity i.e. a separate baseline hazard was computed for each stratum. Besides the random sire effect, the model included the fixed time independent effects of age at first calving, herd size and region as well as the time dependent effects of relative milk production and year*season of first calving. The highest impact on longevity was found for relative milk production. Cows with the lowest milk yields were at approximately 2.7 times higher risk of culling compared to cows with average milk production. Effects of age at first calving, herd size and country region had lower impact on longevity. Sire variance was 0.023 which results in a heritability of 0.06 for functional length of productive life. The average approximate reliability of estimated breeding values was 0.49. Genetic trend showed no clear tendency by year of birth of bulls.
National genetic evaluation of lengh of productive life in Slovakia was carry out from the year 2014 till 2018, three times per year (March, June and October). The survival analysis was performed using Weibull sire model. The heritability obtained from Weibull model was different between populations (0.13 in Holstein and 0.05 in Slovak Simmental, respectively). RBVs of Holstein sires born up to 1999 shows decreasing tendency in all five years. A desirable tendency started from the year 2000. Differences between RBV in particular years are due to descent censored records during the evaluated period. Similar trends showed in Slovak Simmental bulls RBVs. Culled cows reached average 305-day milk yield 6499 kg and 4645 kg in Holstein and Slovak Simmental breeds, respectively. The length of productive life there was 898 days in Holstein and 985 days in Slovak Simmental cows. Age at first calving reached 930 days in Slovak Simmental and 851 days in Holstein heifers. The progress of both traits in the years 2014–2018 was lower in Holstein population, +288 kg milk and +76 productive days than in Slovak Simmental cows.
Censored Bayesian models for genetic evaluation of age at first calving in Brazilian Brahman cattle