Using Milk Fat and Protein Percentages to - Evaluate Herd Nutrition and Health
Using Milk Fat and Protein Percentages to
Evaluate Herd Nutrition and Health

Dr. Allen Young
USU Dairy Extension Specialist

    Lately I have dealt with several problems related to fat and protein levels in milk and felt that a quick primer might be useful.

    I don’t know why the usefulness of milk fat and protein went “out of style.” I constantly hear dairy farmers say they don’t need them. They say that milk weights and somatic cell counts are the only important information that they need. I obviously disagree or I wouldn’t be writing this article. Milk component percentages are very sensitive indicators of changes/problems in feeding and health. In a condensed form, here is what I think evaluating these components can do for you.


    The level of fat in milk is primarily an indicator of acetic acid formed in the rumen. The primary source is from fiber (found mainly in forages). Supplemental dietary fat can also change milk fat composition. It can also be an indication of weight loss or gain by the dairy cow. Excessively low or high fat % can indicate altered rumen function which can be a warning of serious health problems developing in the cow.

    Reduced milk fat %, probably due to decreased fiber intake, can lead to such health problems as acidosis and laminitis. If your milk fat % is lower than 3.0 % (Holsteins), then you can’t afford to sit by and watch. You need to determine the cause of the problem. Many times the problem can be traced back to forage which has been chopped or blended too fine, sorting by the cows, or poor hay that the cows won’t eat. The worst acidosis and laminitis case I have ever seen was one where the farmer was feeding severely rain damaged hay in the feed bunk and grain through the computer feeder. The cows were eating the grain, but almost totally ignoring the hay. In addition to watching fat %, abnormal fat:protein ratio is another good indication that you are heading for a problem. Fat:protein inversion (i.e., protein level equal to or greater than fat level) can indicate that the rumen is not functioning properly and can be an early warning sign which allows you to make corrections before major damage is done. Herds in which I have seen acidosis and laminitis have had a significant number of cows with inversions and changes in the fat:protein ratio.

    Lately I have been told that the fat % from DHIA is no good and that it is of no use because it is grossly different from the fat % recorded by the milk plant. If this is the case it is usually due to problems in sample collection at the dairy. Almost all such problems I have seen lately are a result of difficulties with the milking equipment in the parlor which make it nearly impossible for the DHIA technician to do a proper job and get a sample which is representative of the level of fat in the milk. If the DHIA test and milk plant values are not reasonably close, it is the responsibility of the dairy producer to make sure that the discrepancies between the two are worked out. Not making an effort to correct problems with sample collection is a major management short-coming and wastes your money.


    I doubt that most people complain about milk protein levels being too high, but they are definitely missing out on income if the protein level is too low. If milk protein levels are too low (less than 3.0% for Holsteins), then it is probably due to one of two possible reasons. The first is a ration protein level that is too low. For the vast majority of producers, that is not a likely scenario. The second is that the level of energy in the ration is too low. This is a more likely probability.

    A good “one-two punch” for monitoring ration protein levels is to use milk protein % in conjunction with the Milk Urea Nitrogen test (MUN). Between the two, you should be able to get a fairly clear picture of how well your cows are utilizing the ration that you are feeding. In the future, MUN will become even more important in providing a benchmark for the level of true protein in the milk, rather than just relying on total protein.

    Lastly, lactation curves for milk components (fat and protein) are normally the inverse of the milk lactation curves. This means that component curves decrease to 50 - 60 days in milk and then begin to increase again as days in milk increases. Milk curves peak at about the same time as component curves reach their lowest point.

    Although this is a very brief example of what components can do for you, I hope it makes you think about how you might use this information to help make better management decisions. Alterations of the rumen environment can lead to costly health and economic problems. Monitoring milk components is your first line of defense, and is more sensitive to ration/eating disorders than anything else you might use.