cjs-202303-0003 ArticleInAPeriodical 2023 Czech Journal of Animal Science 68 3 99-110 FaltaDaniel ZapletalováLenka HanušOto KučeraJosef VečeřaMilan ChládekGustav FilipčíkRadek KopecTomáš Stefanus LateganFrancois The interaction between the milk production, milk components with a low frequency of analysis and factors affecting the milk composition in dual-purpose Simmental cows The aim of this study was to improve the understanding of the contribution of components typically found in milk, but which are not often included in analyses, to the nutritional status of dairy cows. This was undertaken by analysing the amount and composition of milk produced by Simmental dairy cows, a dual-purpose breed farmed in the Czech Republic. Apart from the more frequently analysed group of components in milk, a less frequently analysed group of components were also investigated. This group, typically, consists of the following components: urea, casein, citric acid, beta hydroxy butyrate (BHB) ketones and free fatty acids. The average content of urea, casein and citric acid in milk is 25.75 mg/100 ml, 2.96%, 0.15%, respectively. The influence of environmental factors on these indicators was evaluated, as well as the degree of hereditary establishment. These less frequently analysed components (indicators), as well as the more frequently analysed components of milk, are subject to several external influences, especially the influence of the breeder, the year and the season of calving. The content of these components varied significantly statistically during the lactation period and also in the order of lactation. The influence of a cow's individuality and the degree of additive genetic background are evident, with estimated heritability coefficients ranging from 0.04 for the BHB ketone content to higher values, e.g., 0.28 for citric acid or 0.31 for the lactose content in milk. The relationships between the components of milk and the daily milk yield were also evaluated, and statistically significant negative correlations were found between the content of casein and the daily milk yield (-0.47) and between the lactose content and the number of somatic cells (-0.37).