Variation in the Constituents of Milk Under Arizona Conditions. III. Variation in Milk from Jersey, Guernsey, Holstein, and Mixed Herds

Abstract

Total solids, serum solids, fat, and protein values were highest in winter and lowest in summer. The milk from Jersey and Guernsey herds, containing 4.91 and 4.36 per cent fat, respectively, showed no definite trends in lactose content in relation to other constituents. The milk from the Holstein and mixed herds had a slightly lower lactose value during the summer, with an increase in the fall and winter months. The serum solids content of milk from Holstein cows Was below 8.5 per cent during 6 months of the year. This decline occurred in summer and was accompanied by decreases in total solids, fat, and lactose. Serum solids content of the milk from Jersey, Guernsey, and mixed herds also averaged lowest in summer, but was still above the legal minimum, except for mixed herds, which had an average of 8.48 per cent serum solids in August. The average chloride values were 0.152 for the Holstein herds, 0.134 for the mixed, 0.128 for the Guernsey, and 0.110 per cent for the Jersey herds. The chloride values were highest in summer and lowest in winter. Cows on marginal rations and consequently not in good physical condition produced milk which is considered normal in composition and averaged only slightly lower in total solids, fat, and lactose, essentially the same in serum solids, and slightly higher in the protein content and in specific gravity. Herd samples of milk representing one day's production may be abnormally low in serum solids but well above the minimum in fat. © 1947, American Dairy Science Association. All rights reserved.