WildAgain Wildlife Rehabilitation, Inc.

Milk replacers for wildlife


Rancidity Issues with powdered milk replacers

The Peroxide Value (PV) of an oil or fat is used as a measurement of the extent to which rancidity reactions have occurred during storage. Other methods are available but peroxide value is the most widely used.


The molecular structure of fats and oils play a role in autoxidation. Oils with a high degree of unsaturation are most susceptible to autoxidation. The best test for autoxidation (oxidative rancidity) is determination of the peroxide value, as peroxides are intermediates in the autoxidation reaction. Autoxidation is a reaction involving oxygen that leads to deterioration of fats and oils which form off-flavours and off-odours. Peroxide value, which is the concentration of peroxide in an oil or fat, is useful for assessing the extent to which spoilage has occurred.


The peroxide value is defined as the amount of peroxide oxygen per 1 kilogram of fat or oil. Traditionally this was expressed in units of milliequivalents, which has been commonly abbreviated as mequiv or even as meq. Correlation of rancid taste and peroxide value depends on the type of oil and is best tested with taste panels. The odors and flavors associated with typical oxidative rancidity are mostly due to carbonyl-type compounds.


It should be noted that peroxide values are not static and care must be taken in handling and when testing samples. It is difficult to provide a specific guideline relating peroxide value to rancidity. Peroxide values of fresh oils are less than 10 milliequivalents /kg, when the peroxide value is between 30 and 40 milliequivalents/kg, a rancid taste is noticeable. High peroxide values are a definite indication of a rancid fat, but moderate values may be the result of depletion of peroxides after reaching high concentrations.

PetAg’s Esbilac® and KMR® powdered milk replacer products contain unsaturated fats that are highly perishable. Since these products contain no preservatives, rancidity could easily develop if the products have been exposed to high temperatures during transportation and storage, especially during the heat of the summer. They can also spoil if not properly handled by the consumer. Ppowdered milk replacer products produced by other manufacturers that contain preservatives are also susceptible to spoilage if not stored properly.

While a consumer’s detection of an off-odor or strong odor is a strong indication of the presence of rancidity (the oxidation of fats), a more scientific way is to measure the peroxide value of the product. Peroxide Value (PV) is the most widely used indicator of fat oxidation.  A peroxide value is required only for USDA certified edible animal fats, such as tallow or lard. However, the feed industry also uses PV to assess the stability or rancidity of fats used as feed ingredients, by measuring lipid peroxides and hydroperoxides formed during the initial stages of oxidation.  Values are reported as meq of peroxide per kg of fat. 


Figure F-1. Esbilac® powder - peroxide value test results..

Esbilac® test results

PV tests were conducted by Midwest Laboratories on eight Esbilac® powder samples (2 of the 'old' multi-step dry lots and 6 of the 'new' single-step spray dry lots). The results, as shown in the chart below, indicate the PV tests relative to the standards for the maximum level for edible vegetable and animal fats as established by the Codex Alimentarius Commission (Food and Agricultural Organization of the U.N. and the World Health Organization).

As shown in Figure F-1, neither of the samples of the ‘old’ Esbilac® powder exceeded the maximum standard value for PV. However, one third of the samples for the ‘new’ Esbilac® powder did exceed the maximum value, with one lot sample exceeding it significantly.


KMR® and rancidity

About the same time that rehabilitators were trying to identify possible problems with the ‘new’ Esbilac® powder, reports of rancidity were emerging about KMR® powder, another PetAg milk replacer, used to make formula for orphaned kittens. 

PetAg placed a statement on its website  (http://petag.com/news_detail.asp?RegID=15) that said:

“High heat stresses these types of products [KMR® and Esbilac®]. These high heat conditions may occur in transit, in warehouses, in in-store storage, in your automobile, or in your house. PetAg, Inc. tests all of these products before leaving its warehouse to assure that they meet specifications and are suitable for use. Changes occurring after leaving the PetAg warehouse can only be noted by the consumer.

BEFORE using KMR or Esbilac Powders you should always: Examine it visually for any off colors. If the color is extremely yellow, please call. Sniff to determine if the product smells right to you (milk replacement powders should have a bland, somewhat milky aroma). If the aroma is strong, smells old or smells like something other than milk, please call. Reconstitute the product in water and look at and sniff it again. If it does not mix well, it looks or smells different from what you are expecting, there may be a problem so please call.

If the animal you are feeding is hesitant to take the formula or develops diarrhea, please call. It may or may not be a problem with the formula but either way we would like to know so that we may be able to help you with pointers for feeding your newborn or send replacement product if necessary.” 

An interview with Darlene Frudakis, the PetAg President, conducted by 575magazine.com, an online news service, in December, 2009

 confirmed that there had been some spoilage with a few packages of KMR® powder. She said that PetAg had recently changed their manufacturing process in order to reduce the problems that could occur as a result of exposure to heat. While she did not describe the change in the interview, communication with PetAg confirms that they started producing KMR® powder in the summer of 2009 with the same single step dry method at the manufacturing facility where they are manufacturing the Esbilac® powder.


Products from other manufacturers

The chart at right indicates the Peroxide Value test results for some of the other powdered milk replacer products from other manufacturers, as well as from PetAg. As can be seen, the products that contain preservatives, as a group, have a much lower observed incidence of elevated Peroxide Values.

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.)


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