Non-additive effects on milk production in Czech dairy cows.

Crossbreeding effects on milk production traits of Czech dual-purpose and dairy cattle breeds were estimated. Nearly 370,000 cows with known gene proportions from Czech Pied, Ayrshire or Holstein cattle were selected from the national milk recording data base. Single-trait animal models were calculated for milk, fat and protein yield, fat and protein content. The model of Dickerson including additive, additive maternal, heterotic and recombination effects was used for the part of the animal model describing the crossbreeding effects in all calculations. For milk yield, the additive genetic effect (defined as deviation from Czech Pied cattle) was 850-900 kg for Holstein and 240-480 kg for Ayrshire. The maternal effects were low and negative. Low significant positive heterotic effects were observed being up to approximately 100 kg for Czech Pied x Holstein. The recombination effects were negative and statistically significant for Czech Pied x Holstein. The results for fat and protein yield were similar to the results for milk yield. For fat and protein content, nearly no statistically significant crossbreeding effects were found.