Estimation of genetic, environmental and phenotypic trends of milk production traits in Holstein cattle of Hamedan province

The present study was conducted to estimate genetic parameters and genetic, environmental and phenotypic trends of milk production traits in Holstein cattle of Hamedan province. In this study 11986 305-d records of first three parities of Hamedan province Holstein cattle, which were gathered during 1990-2011, were used. Variance-covariance components and breeding values were estimated using animal mixed model, based on Average Information algorithm of Restricted Maximum Likelihood (AI-REML). Herd-year-season and parity were fixed effects and directs additive and permanent environmental factors were considered as random effects. Heritability estimates for milk yield, fat corrected milk yield, fat percentage, protein percentage, fat yield and protein yield were 0.16, 0.14, 0.20, 0.11, 0.15 and 0.13 and their repeatability estimates were 0.44, 0.39, 0.31, 0.20, 0.35 and 0.39, respectively. Genetic trends of these traits were, 3.42 kg/yr, 2.51 kg/yr, -0.002 %/yr, -0.000 %/yr, 0.082 kg/yr and -0.020 kg/yr, environmental trends were 85.89 kg/yr, 67.61 kg/yr, -0.028 %/yr, -0.007 %/yr, 1.12 kg/yr and 1.62 kg/yr and their phenotypic trends were 89.54 kg/yr, 70.26 kg/yr, -0.030 %/yr, -0.007 %/yr, 1.22 kg/yr and 1.69 kg/yr, respectively. The results of this study showed that the production traits of Hamedan province Holstein cattle did not have noticeable genetic improvements in past years and most of milk and fat yield increment have been induced by improvement of environmental conditions.