Abstract
Abstract. The aim of the paper was to establish reproductive traits and their heritability during the three successive generations of Holstein-Friesian cattle. Research was conducted on the duration of pregnancy, service period and fertility intensity. In each generation there were 135 first calved cows. Service period and fertility intensity refers to the following calving. Significant differences were established (P < 0.05) regarding duration of pregnancy between I and II generation. Significant (P < 0.05) influence of season on duration of pregnancy and service period was established in I generation (1991), on duration of service period and fertility intensity in II generation (1996) and on duration of pregnancy and service period in III generation (2000). Season effect (summer) was established for all traits of fertility in II generation (P < 0.05). The season (spring) had influence on duration of pregnancy (P < 0.05) and summer had an influence on duration of service period and fertility intensity, and winter effected the duration of service period (P < 0.05) in III generation. Values of heritability coefficients are pretty low for all generations. Considerably greater values for heritability were established for service period and intensity of fertility of cows per generations.
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