Finding models to improve production is a continuous process in order to secure stable and long-term milk production. The increase in milk production per cow results in the need for fewer cows, and consequently in a shortage of calves for fattening. Calves of dairy breeds that will not be used for the replacement of the herd, except as fattening calves, have no significant economic value. In recent decades, there has been an increasing interest in the technology of crossing dairy cows with bulls of meat breeds to ensure calves with more desirable fattening properties and higher selling prices. Out of 1,717 managers of dairy farms, it was determined that only 22,89% of managers were familiar enough with the technology of crossing dairy cows with bulls of meat breeds, and the hypothesis of lack of knowledge about the technology among dairy farm managers was confirmed. Due to a lack of knowledge or wrong information, only 9.4% of managers stated their willingness to implement the crossbreeding program. 15.8% of managers applied crossbreeding technology, of which 44.5% believe that crossbreeding can contribute to the profitability of the dairy farm. From the obtained results, it is concluded that there is a great need for the education of managers of dairy farms in the field of crossbreeding technology. The possibility of applying the crossbreeding technology was investigated by the replacement rate with the hypothesis that it is possible to crossbreed up to 30% of Holstein cows in the herd. The hypothesis was not confirmed due to the determined high replacement rate (44.64%), low fertility (67.4% - 69.6%), and the share of female calves kept in breeding compared to the number of calved cows (45.1% - 46%). Crossbreeding of up to 30% of cows in the herd of Holstein farms is possible only with the application of artificial insemination of cows with sexed Holstein semen to ensure sufficient female replacement offspring. The economic validity of the application of crossbreeding technology on 30% of the maternal herd of cows on Holstein farms was confirmed by analyses of economic indicators of farm operations obtained from a survey in 44 Holstein farms. Economic indicators confirmed the positive contribution of the application of crossbreeding to the successful business of Holstein farms, with the fact that the contribution was more significant in farms with a smaller number of cows and lower milk production per cow. The influence of breed structure and size of dairy herds on lactation income was analyzed using 386,916 standard lactation (305 days) of Holstein-only, Simmental-only farms, and farms with these two breeds (dual-breed farms). Holstein cows in Holstein farms had a higher production of milk (936.2 kg), milk fat and protein compared to Holstein cows in two-breed farms, and consequently, a higher average lactation income of HRK 1,772.75. Simmental cows in Simmental farms produce a smaller amount of milk (473.7 kg), milk fat and protein compared to Simmental cows in dual-breed farms, and consequently Simmental cows in two-breed farms achieve a higher average lactation income of HRK 1,055.31. The results indicate that Holstein cows have better, and Simmental cows have lower milk yield properties in single-breed farms, and consequently, Holstein cows achieve higher and Simmental cows lower lactation income in single-breed herds. The size of the farm has a great influence on milk yield properties, probably because milk production on farms with a larger number of cows is carried out at a higher level of technology and management, therefore cows on larger farms have more desirable milk yield properties. The hypothesis that the breed structure and herd size of farms affect the milk yield and lactation income of dairy cows was confirmed. The influence of calf gender on milk yield properties of Holstein and Simmental cows was also investigated. The analysis showed that cows that gave birth to female calves in the first lactation had higher milk yield (p<0.0001), but a slightly lower proportion of milk fat and protein (p<0.01). A positive influence of the female calf on milk yield in the second lactation was also determined (p<0.0001). The hypothesis that by managing the gender of calves it is possible to increase milk production and lactation income of dairy cows was confirmed. Cows of both researched breeds that gave birth to female calves in their first pregnancy had better milk yield properties and consequently, higher lactation income.