| dc.description.abstract | The aim of this study was to investigate the phenotypic and genotypic evolution of the milk production of a Serbian Holstein Friesian population, also in the aspect of possible future tendencies.
The study is based on milk recording data and data collected by employees of the dairy farm. It includes information of 20,357 lactations, from 1971 to 2008. The number of animals has been increased by approximately nine times. In the population under study the average 305-day lactation milk yield of 6000 kg was increased to about 7340 kg. Parallel the average 305-day lactation fat yield was increased from 208 to 250 6 kg. The average 305-day lacta-tion fat content however decreased from 3.51% to 3.44 % 6.
For the heritability of the traits milk yield in kg, fat yield in kg and fat content in % the values 0.23, 0.32 and 0.39 were calculated. Correspondingly the following-repeatability coeffi-cients were estimated: 0.48, 0.67 and 0.78. The large difference in size between the herita-bility and the repeatability could be a hint for a large permanent environment. The genetic correlations between milk yield in kg and fat yield in kg was 0.91, between milk yield in kg and fat content in % it was -0.50 and between fat yield in kg and fat content in % it was -0.11. The last two values are relatively low.The trend line`s regression coefficient for the breeding value milk yield in kg was 26.66, it means an annual growth of 26.66 kg in average. For the breeding value fat yield in kg, the coefficient was 0.56. The reason for the absolute growth of the fat yield as well of its breed-ing value is the absolute increase in milk yield. The trend line`s regression coefficient for the breeding value fat content in % was -0.0014. The breeding value has decreased by an average of 0.0014 percentage points per year. The main conclusion is that there is barely genetic potential present to feature the trait fat content in % in this population. | en |
