In this study, 55 Holstein cows were used to study biochemical parameters of milk from machine-milked cows, comparing early and late lactation phases. The experiment started on the first day of lactation and lasted for 10 months. To determine milk composition, samples were obtained from each cow on the last day of the first week in month 1 and 2 (early lactation) and month 7, 8, 9 and 10 (late lactation). There was a decrease of milk fat content from the second month and a gradual increase after the 7 th month of lactation. The values for milk fat, pH and total solids were highest during the 9th and 10th months after delivery. The rate of decline of milk biochemical parameters was lower during the last months (between 7-10 months) than during the first months of lactation. In this study, the means of biochemical parameters in milk from machine-milked cows were different from those reported for hand-milked cows and the suckled dairy cows during lactation period. However, the curves followed the same trend regardless of the milking method. From the results, the stages of lactation have significant influence on the milk fat level. Accurate knowledge of lactation curves has an important relevance to management and research on dairy production systems. When definite goals become more clearly established, certain breeds or herds may be determined to be more desirable when selecting for increased total milk yield and biochemical milk parameters.

Key words 
Machine milking, early and late lactation, milk biochemical properties

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