Slovenia is one of the smallest countries with its own breeding programs for Simmental, Brown, Holstein and Beef breeds. Import of foreign genetics is not always the best strategy to improve performance due to the presence of the genotype x environment interaction. In assessing the impact of the environment on the genotype we can use two genetic parameters – genetic correlation and heritability. Excellent rearing conditions with great comfort, high quality feed and good management provide an environment, where largely reflects the genotype (high genetic correlation) and higher heritability. Analysis of the production results and some conformation traits of the offspring of Holstein bulls, which were divided depending on their origin between Slovenia, USA, Canada, Germany and other European countries, indicates the differences of offspring according to the origin of the bulls – father of cows. The offsprings of Slovenian Holstein bulls are both in performance as well as in conformation traits estimates quite similar to the offsprings of German or other European Holstein bulls. In the group of Slovenian Holstein bulls’ offsprings we detected a lot of variability in properties. The offsprings of the USA and Canadian Holstein bulls have achieved better production properties in all categories and also had better conformation traits. We have also found that the offsprings of USA and Canadian Holstein bulls performed above average compared to their peers. But we can’t conclude that their offspring is better from the rest, also due to the lack of the offspring by North-American bulls compared to other groups. Even though the mothers of Slovenian Holstein offsprings had on average poorer production properties and were not assessed as good, their offspring as a result of insemination with Slovenian bulls did not fall behind of the offsprings of Holstein sires from other European countries. Implementation of own selection is therefore reasonable.
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