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The Effect of Environmental Temperature on the Percentage of Fat in Cow's Milk

Department of Dairy Husbandry, University of Missouri, Columbia, Missouri

ABSTRACT

1. Daily data on the University of Missouri dairy herd for a period of 258 days are presented showing the average fat test and environmental temperature. The temperatures ranged from 85.5° to 24.5°F., or a net range of 62°. The average fat tests ranged from 3.171 to 3.600 per cent, or a total difference of 0.489 per cent, and it was generally found that the lower the temperature the higher the fat test. This increase in the fat test amounted to 0.079 per cent for each 10° lowering of the temperature. However, because of the many variables, this result is not considered of as much significance as the results of the controlled temperature trials.
   
2. Seven controlled temperature trials, on two Jersey cows, were run at 10° intervals of temperature, with all other conditions remaining normal. The range of temperature was from 92.7° to 27°F. When the seven periods were taken as a unit, there was a total temperature range of 65.7°, and a total increase in the fat test of 0.624 per cent, or an average increase of 0.095 per cent for each 10° lowering of the temperature.
   
3. In the controlled temperature trials there was a constant increase in the per cent of fat as the temperature dropped below 70°F. From 72.5° to 27° there was a temperature range of 45.5° and a total increase of 0.863 per cent fat, or an average increase of 0.189 per cent fat for each 10° lowering of the temperature. This is almost exactly in accord with preliminary studies at this Station by Ragsdale and Brody, who reported a rise of 0.2 per cent fat for each decrease of 10°F., between the temperature units of 70° and 30°F.
   
4. Above 70°F., there was an actual increase in the fat test. The reason for this is not known, but it is believed to have been due to increased metabolism, induced by higher temperature or the result of disturbing the animals by the sudden changes from one temperature to another. The latter is indicated by the fact that the first day's test in each trial was abnormally high. When these first days were eliminated the increase in the fat test was not nearly so pronounced. It would seem that there is a range of temperature between 70° and 90°F. within which the lowest testing milk is produced. A variation in the environmental temperature either way will bring about an increase in the per cent of fat in cows milk.
   
5. It is believed that the controlled temperature trials are more nearly indicative of the effect of environmental temperature on the percentage of fat in cows milk than the daily herd averages where there were many variables. It is therefore concluded that all other conditions remaining constant, there is an increase of approximately 0.2 per cent fat in cows milk for each 10° lowering of the temperature within the limits of 70° and 30°F. In the second part of this experiment all conditions, other than temperature were apparently effectively controlled and remained constant throughout every change in temperature. Temperature, then, was the only variable.
   
6. It is concluded that temperature is a major factor in the seasonal variation of the per cent of fat in cows milk.
   

¹ Submitted in partial fulfillment of the requirements for the degree of Master of Arts in the graduate school of the University of Missouri, 1925. The author is indebted to Profs. A. C. Ragsdale and Samuel Brody for aid in outlining the problem and for helpful suggestions and criticisms in the preparation of this manuscript.