Genetic analysis for milk yield and reproduction traits of Simmental breed cows

The influence of systematic environmental factors to reproductive and dairy traits, genotypic and phenotypic parameters were studied at four cattle farms in Serbia (Yugoslavia). This research involved 1731 cows that had at least one and up to three lactations maximum. The test included 3856 lactations. The research showed that farm, year, season and the number of calvings in order significantly influenced (P0.01) age variation at fertilization, age at calving and duration of pregnancy. The influence of season was not statistically important (P0.05). The year and calving season significantly influenced servis period and the interval between two calvings (P0.05). Significant impact of the interval between calvings was made by the year of calving (P0.01). Highly important influence to dairy traits was demonstrated by farm, year, season and the number of lactations in order (P0.01) some other influences were not significant. Coefficients of heritability were calculated from the variances by the use of the least square method and for reproductive traits they varied between 0.051 for the interval between calvings and 0.383 for both the first and the second age at fertilization. By the application of the least square methods and BLUP model for the father (bull) were determined low up to average values of the coefficient of heritability except for the milk fat in the third lactation with very high heritability (0.733 and 0.588). This thesis presented the important genetic, phenotypic and environmental correlations between dairy and reproductive traits. The obtained results showed strong up to complete correlation between additive genotypic values of bulls per lactations, contrary to low positive or negative variations among controls. The highest average effects of additive genes for bulls was obtained by BLUP-SM 1 at the first lactation together, whereas the most precise estimation was received by all three lactations together.