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Rancidity In Milk Replacer Powder.

Take a Sniff.



Preparing formula for wild mammal orphans in rehab is often done in a hurry or sometimes delegated since it is considered ‘a necessary but easier task’ and assumed to be ‘low risk.’ Also, since most milk powders have been reliable and the results predictable, mixing them has not seemed to need special knowledge or skill.


In the last six months, WildAgain Wildlife Rehabilitation, Inc. has tested 100+ milk replacer powders – and many more over the years. Since 2008 to present, WildAgain has arranged for a certified independent lab test to test milk powder samples for many things. Those lab tests provided considerable information, but rarely showed elevated peroxide values that would indicate spoilage due to rancidity.

During recent testing of the milk powders, a strong odor was detected from a newly opened can of Goats Milk Esbilac® (GME®). The odor was initially attributed to differences in goat versus cow milk. However, the intense odor prompted WildAgain to request the lab to test the powder for rancidity, along with other tests. Rancidity was confirmed. Five different lots of GME® produced in 2018-19 that were tested showed rancidity. Future test results for milk powders will be posted, including tests on rancidity.


A quick review


1) Any foods containing fats/oils are susceptible to rancidity because their chemistry can make them vulnerable to oxygen damage.


2) “Rancid” is a very general term used to describe a fat that has ‘gone bad’ or spoiled. 


3) Rancidity can occur during shipping or during storage at warehouses (or other locations e.g., rehab facilities).


4) Rancidity can cause a change in odor, palatability, and nutritional quality and value. 


5) Rancidity can compromise safety for consumption. Eating a few meals of a rancid product may cause GI upset, including diarrhea, bloat, nausea and loss of appetite. Regular consumption (such as multiple formula feedings per day) can result in those symptoms progressing or even more serious problems – especially in the very young or those with compromised health.


6) Some wild mammals will refuse to eat rancid foods, including formula, sensing the unpleasant and 'off-odor' and taste. However, if the animal only has the choice of rancid formula or no food at all, it may consume the rancid product instead of starving. If a wild mammal baby is tube fed, it does not have the option to refuse a rancid food.





It is up to the rehabilitator to ensure that the powdered milk replacers are fresh – and not rancid. Hence it is essential for the rehabilitator (or whoever makes the formula) to pay attention to the milk powders in order to prevent use of powders that could be rancid. Rancid milk powder may also have a strong “spoiled” odor, or a more subtle odor, similar to the smell of crayons or soap. Others describe it as wet cardboard, oil paint or wood varnish.


The recent findings from just a handful of samples certainly do not suggest that all GME® powders are rancid. But in light of 5 out of 5 samples of GME® all showing elevated levels of rancidity, it is important that rehabilitators need to examine all of their milk powders (not just GME®), including taking a good ‘sniff’ to detect any off-odors. ﷯


For more a longer discussion on rancidity (including specific product tests) and how to prevent it, click on the rabbit at right.



Action steps if you detect rancidity


If the milk powders have those odors, consider the following steps to take:


1) If the powder at any point prior to use, whether freshly opened or 6 months old since opening, has only a very slight 'off' difference in odor, it may be OK to use if blended with other products to make a formula. If the animals being fed are continually reluctant to eat it or exhibit adverse reactions or symptoms, discontinue use.


2) If a more pronounced and offensive odor is detected, probably consider not using the product.


3) Another step is to contact the point of purchase (retailer, manufacturer) and discuss the problem. Ask for a replacement. Return the product if requested, as the manufacturer may want to perform lab tests.


4) Ask your network of rehabilitators to see if the problem is occurring elsewhere and how prevalent with the specific product and lot number.

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