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The Freezing Point of Milk -- A Potentially Hot Topic
Dairy Pipeline: July 1999
Ernest Hovingh
Extension Veterinarian
Virginia-Maryland Regional College of Veterinary Medicine
Virginia Tech
(540) 231-5234
ehovingh@vt.edu
The most obvious way in which the freezing point (FP) of bulk tank milk can be altered is by the deliberate or accidental addition of water to the milk after it leaves the cow, and this is why there are regulations and standards in place. However, in some circumstances a cow can produce milk that has an abnormal FP, and if this happens with enough cows in a herd it could affect the bulk milk freezing point. The FP of milk is determined by a large number of factors, many of which are inter-related. FPs can vary by time of day, season of the year, stage of lactation and breed. Geographic region (north vs. south) and 'heat stress' can also have an effect. Dietary factors can also play a very significant role in determining the FP of milk -- research has shown that milk from cows fed energy deficient diets (as well as diets with low energy densities) or diets with low salt concentrations had an elevated FP. Given the complexity of the factors affecting the FP of milk it is difficult to make general recommendations for producers who may be concerned about their bulk milk freezing point. After ensuring that there are no deliberate or accidental additions of water to the milk ('chasing' residual milk with water or improper drainage of milk lines for example) and that the milk is not freezing in the bulk tank, a nutritional assessment should be carried out. Finally, the health status of the cows should be examined to determine if there are any metabolic or udder health abnormalities, or if there is a significant amount of heat stress. This approach should help to identify the most common causes of an altered freezing point of bulk tank milk.