Linear vs. piecewise Weibull model for genetic evaluation of sires for longevity in Simmental cattle

Abstract

This study was focused on genetic evaluation of longevity in Croatian Simmental cattle using linear and survival models. The main objective was to create a genetic model that is most appropriate to describe the longevity data. Survival analysis, using piecewise Weibull proportional hazards model, used all information on the length of productive life including censored as well as uncensored observations. Linear models considered culled animals only. The relative milk production within herd had a highest impact on cows' longevity. In comparison of estimated genetic parameters among methods, survival analysis yielded higher heritability value (0.075) than linear sire (0.037) and linear animal model (0.056). When linear models were used, genetic trend of Simmental bulls for longevity was slightly increasing over the years, unlike a decreasing trend in case of survival analysis methodology. Average reliability of bulls' breeding values was higher in case of survival analysis. The rank correlations between survival analysis and linear models bulls' breeding values for longevity were ranged between 0.44 and 0.46 implying huge differences in ranking of sires.

Genetic evaluation for functional longevity in Polish Simmental cattle

“…the environmental and genetic effects. Our estimates of Weibull parameters, the shape parameter (ρ) 2.25 and the intercept (ρlogλ) −15.14, were in the range of values reported by Sasaki (2013) for longevity traits in dairy cattle, and were similar to results obtained for Simmental populations (Jovanovac et al 2013;Raguz et al 2014). Such values of these parameters (with ρ > 1) demonstrate the age-linked increase of cows' culling risk.…”

“…The equivalent heritability (0.09; Table 2) accounting for the level of censoring (Eq. 4b), was higher than heritabilities between 0.06 and 0.08 reported in other studies of Simmental cattle longevity (Jovanovac et al 2013;Strapakova et al 2013;Raguz et al 2014). The moderate heritability supports the possibility of selection for functional longevity in Polish Simmentals.…”

Genetic Trend of Length of Productive Life in Holstein and Slovak Simmental Cattle in Slovakia

“…Increase in sire breeding values is distinguished. Genetic trends of LPL sires of two breeds in Slovakia were similar in compare with many authors (van Doormaal, 2009;Raguž et al, 2014;Egger-Danner et al, 2015;Stanojević et al, 2018;Morek-Kopeć et al, 2017). The negative genetic trends in functional longevity found Imbayarwo-Chikosi et al (2017) in South Africa Holstein cattle and Jenko et al (2013) in Slovenian Brown cattle, which could have been resulting from intense selection on high milk production.…”

“…The holstein sire variance obtained in Weibull model was similar as stated Sewalem et al (2005) (0.046) and Imbayarwo-Chikosi et al (2017) (0.047). Raguž et al (2014) and Morek-Kopeć and Zarnecki (2017) found higher Simmental sire variance in compare with our results (0.03 and 0.069).…”

“…Identical heritability found Caraviello et al (1999). Raguž et al (2014) and Morek-Kopeć and Zarnecki (2017) computed similar heritability in Simmental population (0.075, 0.09, respectively).…”