| Summary: | Using three-breed rotational crossbreeding in a purebred Holstein (HO) herd raises two questions: Do the different genetic classes of cows generated by crossbreeding perform differently? Are there any economic benefits of combining them within a herd? This study aimed at comparing the performance between the different genetic classes resulting from the use of three-breed rotational crossbreeding, and simulating the effect of combining them on herd profitability. Based on a dataset of 14 French commercial dairy herds using three-bred rotational crossbreeding from a HO herd over a 10-year period, we defined three genetic classes according to the theoretical value of heterosis and the percentage of HO genes. We performed linear models and estimated least square means to compare HO cows and the first and second generation of crosses (F<sub>1</sub> and G<sub>2</sub>, respectively) on eight performance characteristics related to milk yield and solids, udder health and fertility. We used these to simulate profitability of five herd compositions differing according to HO, F<sub>1</sub> and G<sub>2</sub> proportions. We showed that HO, F<sub>1</sub> and G<sub>2</sub> cows had different and complementary performance profiles. HO had a win-lost trade-off between milk yield and fertility, G<sub>2</sub> had the opposite trade-off and F<sub>1</sub> had a win-win trade-off. Differences regarding milk solids and udder health were less clear-cut. We highlighted that combining HO with F<sub>1</sub> or with both F<sub>1</sub> and G<sub>2</sub> (below 30%) could be more profitable than using purebred HO or crossbred herds in a conventional milk price scenario. These findings provide evidence on the benefits of functional diversity generated from the use of dairy crossbreeding in dairy herds.
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