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Variation in the Constituents of Milk Under Arizona Conditions. I. Variations of Individual Cows within Breeds by Calendar Months

Department Of Dairy Husbandry

A. B. Caster and R. H. Kellner¹

Department of Agricultural Chemistry and Soils, University of Arizona, Tucson

ABSTRACT

1. In general, a corresponding rise was noted in the total solids, serum solids, and protein when the butterfat content increased, except that in some cases samples were abnormally high in fat and low in serum solids.
   
2. An increase in the protein content was accompanied by increased butterfat, total solids, and serum solids, and by a decrease in the ratio of fat to serum solids.
   
3. An inverse relationship existed between milk production and total solids, serum solids, and butterfat percentages of the milk.
   
4. In general, an inverse relationship was present between the lactose and the protein percentage of the milk.
   
5. The total solids, butterfat, and serum solids content of the milk was higher in winter and lower in summer. The difference presumably is due mainly to the higher environmental temperatures of the summer months.
   
6. The lower butterfat test of the Guernsey milk is due primarily to the higher environmental temperature. Milk from Guernsey cows had the greatest variation in fat test by season of the three breeds studied.
   
7. Environmental temperatures appear to exert a greater influence on milk and butterfat production than does the advancing stage of lactation.
   
8. The percentage of samples of milk falling below the minimum state requirement for serum solids and fat, respectively, were: Holstein, 47.5 and 22.7; Guernsey, 2.2 and 0.6; Jersey, 2.5 and 0.
   
9. Using averages for all animals as the basis of calculation, the butterfat content of milk decreased 0.1 per cent for each 10° rise in mean maximum temperature between 65 and 105° F. under Arizona conditions.
   
10. A Jersey cow family was found to produce milk 0.31 per cent lower in lactose than normal for the Jersey breed.
    

¹ Resigned July 1, 1942.