Certain reproductive and performance traits of first calving Simmental cows, as well as the demonstration of those traits depending on the participations of different proportions of Red Holstein-Friesian genes (HF), were investigated. The investigation included 176 first calving cows, divided according to percentage of HF genes, in 5 groups (0%, 12,5%, 25%, 37,5%, 50%). Statistical analysis of data was done by method of Least squares (LSMLMW, Harvey, 1989). The effect of age at first fertilization was highly significant variated between groups of first calving cows and the youngest was in the fifth group (the group with 50% of HF genes), which were fertilized at 520,8 days. The average age at first conception for alln examined groups was 536,7 days. Least squares results shown that different proportion of HF genes was not significant (P>0,05) body weight of calves. The least body weight of calves was in group of first calving cows with 50% HF genes. The duration of pregnancy was 283,3 days and between different groups were not significant (P>0,05). The biggest values of service period and lactation were in the fifth group. The average period of lactation was 321,32 days and the longest (348,5 days) were established in fifth group cows 50% IIF genes. The average milk yield was 4224,34 kg with 3,83% milk fat or 4116,6kg 4%FCM. Cows with 50% HF genes produced more milk compared to the cows in other groups. Established results have shown that with increasing proportion of HF genes service period between calving interval and duration of lactation were longer. Also, with increasing of proportion of HF genes the milk yield and yield milk fat were raised while percent of milk fat was lower.Ispitivane su reproduktivne i proizvodne osobine prvotelki i meleza dobijenih meliorativnim ukrštanjem simentalske i crveno-bele holštajn-frizijske rase. Ukupno je ispitivanjem bilo obuhvaćeno 176 prvotelki podeljenih u pet grupa-sekcija, razvrstanih prema udelu gena crvenog holštajna (HF-RED) u simentalskoj rasi. Analiza uticaja udela gena crvenog holštajna (0%, 12,5%, 25%, 37,5%, 50%) na posmatrane reproduktivne i proizvodne osobine obavljena je metodom najmanjih kvadrata (LSMLM.W, Harvey 1987). Dobijeni rezultati pokazuju daje udeo gena crvenog holštajna imao značajnog uticaja (P lt 0,01) na sve ispitivane proizvodne osobine (trajanje laktacije, proizvodnju mleka i mlečne masti u celoj i standardnoj laktaciji, procenat masti u mleku i proizvodnju 4%MKM) kao i uzrast grla pri prvoj oplodnji i trajanje servis-perioda. Masa teladi pri rođenju i trajanje bremenitosti nisu značajno (P>0,05) zavisili od učešća HF-RED gena
