Powdered Milk Replacers Rancidity - Detection and Mitigation (updated Sept 2022)

Human taste buds are very sensitive to the unpleasant odors or unpalatable flavors of rancid foods, and thus we choose to avoid eating them. Taste is directly influenced by the sense of smell, and the human olfactory is comprised of about 5-6 million receptors. For reference, rabbits have about 100 million and dogs a whopping 220 million.  Young mammals also have a keen sense of smell.  However, when they are being fed a milk replacer formula as a single food source, their hunger may transcend their instinct to avoid a rancid formula.  There are various reasons that animals may resist or refuse to eat a previously successful diet or formula.  One possibility could be that the food or product is rancid.  This can occur either in a newly opened package or an opened container that has had excessive exposure to oxygen. With animals being tube fed, taste is not a factor, but rancidity can cause adverse medical issues.

 

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Dietary consequences

 

Consuming just a few meals of a rancid product may cause gastrointestinal upset, including diarrhea, nausea and loss of appetite. However, consumption of rancid products over a longer period can result in much more serious problems.  These can include severe digestive disturbances, poor growth rate, weight loss, skin problems, hair loss, anorexia, emaciation, intestinal hemorrhage, degeneration of the heart, enlarged liver, death, and more.

 

While conducting research on milk replacer powders, WildAgain consistently examines the powder colors, texture, agglomeration, and odors. If off-odors are detected, arrangements are made for the independent lab to conduct peroxide value tests (described below) to assess rancidity. Most of the cans/packages that were tested for rancidity by the lab during the 2008-2010 time frame did not show elevated peroxide values that could indicate spoilage. During the testing of late 2019 and early 2020, cause did not arise to test for rancidity. However, subsequent testing has shown elevated rancidity as shown in the chart below, especially in GME and KMR. 

 

It should be noted that elevated peroxide value levels may occur in any milk powder produced by any manufacturer, including products that contain preservatives. Since spoiled food can cause a variety of health problems, wildlife rehabilitators are encouraged to use effective storage practices and closely examine the milk replacer powders as part of their general practice.

 

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Storing milk replacer powders

 

Milk replacer powders, like other foods, are perishable. While gastrointestinal upset may develop for people and other mammals that eat spoiled food, the consequences of eating spoiled food may be more serious for the very young. Thus it is essential that wildlife rehabilitators using milk replacers take the following precautions to prevent product spoilage:

 

1.) Always check the storage recommendations for milk replacer powders or formulas.  These can be found on product label or on the manufacturer’s website.

 

2.) Store unopened milk replacer powders in a cool room, refrigerator or freezer. Packages of opened milk replacer powders should be stored in refrigerators or freezers. Milk replacer products tend to have high levels of fats. Such fats may spoil if the powder is exposed to high heat.  This can occur in warehouses, transit vehicles (trucks, cars, ships, planes, cars, etc.), stores, storage facilities, homes or even on a kitchen counter during a hot summer day. Some rehabilitators prefer to order milk replacer powders during cooler seasons to reduce the risk of exposure to high temperatures during shipping.

 

3.) Oxidation is another cause of rancidity in milk products. This could occur if the milk replacer powder is exposed to considerable air, such as if the package is left open. Some rehabilitators purchase milk replacer powders in bulk and then divide it into smaller packages, either for distribution to other rehabilitators or for easier storage in freezers. If milk replacer powders are ‘repackaged’ into smaller containers, vacuum sealers may reduce the potential for oxidation and lengthen storage.

 

4.) Keep milk replacer powders in a dry environment.  They may also spoil if they become wet or are exposed to excessive dampness. This could cause excessive clumping, discoloration, mold, or other signs of spoilage.

 

 

Rancidity tests (peroxide values)

 

The following chart shows the product lots that have been tested by the lab for the peroxide value. The dotted blue line on the chart indicates the maximum levels established for edible oils and fats by Codex. The specific reference for this value is included in the Codex Standard for Named Animal Fats (CODEX-STAN 211-1999) and the Codex Standard for Named Vegetable Oils (CODEX-STAN 210-1999.)