Production traits of Romanian Simmental cows at first lactation.

Ninety-nine first lactation cows of the Romanian Simmental breed were used in a 305-day lactation period to study the production traits of the breed and its potential for genetic improvement. The phenotypic parameters studied were milk, fat and protein yield, as well as fat and protein percentage; variance components were calculated. The milk yield in the dairy cow population was 4053 ± 1391.8 kg, whilst the fat and protein yield were 157.6 ± 55.3 kg and 131.6 ± 46.3 kg, respectively. Phenotypic correlation between milk yield and milk fat yield was high (r = 0.9973) and between milk yield and milk protein yield was relatively low (r = 0.1403). In addition, correlations obtained between milk yield, and milk fat and protein percentages were low (r = 0.0519 and r = 0.0022, respectively), whilst the correlation between milk fat yield and milk protein yield was weak (r = 0.1414), and between milk fat percentage and milk protein percentage was moderate (r = 0.5139). The strong phenotypic correlation between the milk yield and milk fat yield indicates that the population of dairy cows can be improved by selection using the independent level of selection.