Crossbreeding effects were estimated from a sample of nearly 370000 cows with known gene proportions from Czech Pied, Ayrshire or Holstein cattle. Single-trait animal models were calculated for milk, fat and protein yield, fat and protein content. The model of Dickerson including additive, maternal, heterotic and recombination effects was used. For milk yield, the additive genetic effect (defined as deviation from Czech Pied cattle) was 850 to 900 kg for Holstein and 240 to 480 kg for Ayrshire. The maternal effects were low and negative.