Variation in the Constituents of Milk Under Arizona Conditions. II. Influence of the Month of Lactation in Cows of Different Breeds

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Abstract
A study concerning the effect of the stage of lactation on constituents of milk was made using 11 Jersey, 11 Guernsey and 12 Hol-stein cows. Lactations began in various months throughout the 30-month exptl. period. Data represent 7-10 monthly tests of each lactation. Lactose and protein data were obtained on 4 Jersey, 5 Guernsey and 9 Holstein cows. The data, presented graphically by months of lactation, show increases in total solids, serum solids, fat and protein after the 2d month except in Guernsey milk which had a decrease in the 8th month. A large percentage of the Guernsey cows were in the 8th month of lactation during spring and summer. Serum solids of Jersey milk varied least, followed by Holstein and Guernsey. Milk produced under Arizona conditions averaged lower in all constituents than Illinois-produced milk except for the fat content of Holstein milk.