This study was conducted in five dairy farms with different capacity (farms A with 47, B 12, C 10, D 14 and E 24 Simmental cows, aged between 4 and 5 years and body weight about 600 kg) in order to determine a relationship between rearing system, Animal Needs Index (ANI) and milk traits. Loose system of cow rearing was used in open stalls in farms A and C, while in other farms cows were tied in closed stalls. In two farms, there were outdoor pens, permanently available to cows on farm A, and during daytime on farm D. Rations for dairy cows were equal in all five farms and suitable for daily milk production about 20 kg with 4.0 % milk fat and 3.5 % milk protein. It was established that total ANI scores for farms were A 35.5, B 9.5, C 24.5, D 26.5 and E 10.5. The welfare levels in farms B and E were not sufficient, in farms C and D were very good, while in farm A it was excellent. A very significant influence of rearing system on cow welfare was found (p<0.001). A significant influence of rearing system (p<0.01) on average daily milk yield, milk yield in standard lactation, milk fat (kg), yield of 4 % fat corrected milk and yield of proteins (kg) were noticed. The influence of the rearing system on milk fat content (%), dry matter (%), protein (%) and lactose (%) was not statistically significant. Differences between ANI score, daily and standard lactation milk yield were very significant (p<0.001), as well as differences between ANI and the amount of milk fat (kg), protein (kg) and amount of 4 % fat corrected milk.