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The objective of this study was to analyse the effect of the most important factors affecting growth (body weights of 5-, 12- and 20-week old males and females) in Oravka chickens. In total, 359 individuals of conservation flock (operated by the National Agriculture and Food Centre – Research Institute of Animal Production Nitra) were studied. The mixed model included fixed effects of sex, age, rooster/breeding season, an interaction of sex and age nested within rooster/breeding season and random effect of bird due to repeated weights of each individual. All fixed effects highly significantly (P < 0.01) influenced body weight of birds; repeatability attributable to among-individual variation was estimated to be about 35 % proportion of variance. With respect to rooster/breeding season, body weights in 5-week old birds (between 384.62 ± 32.11 g and 572.04 ± 23.39 g for males vs. between 343.33 ± 35.73 g and 497.71 ± 26.10 g for females) were non-significant (P > 0.05); body weights in 12-week old birds (between 1299.51 ± 26.85 g and 1464.29 ± 23.39 g for males vs. between 1071.90 ± 25.27 g and 1134.83 ± 25.57 g for females) were either non-significant (P > 0.05) or significant (P < 0.05); body weights in 20-week old birds (between 2237.24 ± 31.17 g and 2633.76 ± 47.84 g for males vs. between 1615.77 ± 34.80 g and 2056.84 ± 37.56 g for females) were at least significant (P < 0.05).