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Fox Valley 32/40 - Part 1. Updated lab tests and performance data.

Fox Valley Nutrition manufactures and sells a wide array of milk replacer products for livestock, domestic pets and wildlife in rehabilitation. The 32/40 formulation is a widely used product by many rehabilitators around North America. While the product does not seem to have changed in the past 10 years, a new round of testing has been conducted since this product is used in many wildlife rehabilitator's formula recipes. This article (Part 1) discusses those test results and provides a side-by-side comparison between a 2022 lot and the average of the last 10 lots tested from 2019-2021. Part 2 discusses and offers suggestions on the recent tests, highlighting any major changes (PDF).

Fox Valley 3240 Label.jpg


In conjunction with WildAgain's recent round of in-depth testing of other powdered milk replacers used by wildlife rehabilitators, Fox Valley32/40 was also tested, as it is widely used by small mammal rehabilitators in North America. Very little appears to have changed in the product in at least 10 years.

Part 1. This analysis provides the chemical analysis of a 2022 sample of Fox Valley 32/40 and some of its primary formula preparation performance characteristics such as measurement and reconstitution. It does not assess how the new product will perform when fed to orphaned wildlife in rehabilitation, though some of the information certainly can be used with decisions and use. As a reference point, many of the chemical and physical characteristics are compared to the last 10 lots tested from 2019-2021.

Part 2. An accompanying article discusses some of these test results and offers some suggestions that wildlife rehabilitators may consider when using Fox Valley 32/40.

The following list highlights some of the key findings prior to a more detailed presentation of test results and analysis. 

√ Ingredients. No change in the list of ingredients in at least 10 years. Protein is cow milk based, primarily from casein. No pre- or probiotics, or preservatives, are listed.

√ Proximate analysis. Only slight changes other than a 5 percentage point increase in fat concentration, which now adheres to the Guaranteed Analysis.

√ Ash. As for dietary minerals, very little change. This sample did contain dietary copper, a key mineral, which has been intermittently absent in previous test samples. 

√ Fatty Acids. The profile shows a remarkably high concentration of saturated fats (≈90%) and a corresponding low amount of monounsaturated fats. A benefit for cottontail rabbit formulas.

√ Rancidity. The 2022 sample tested at a low value of 3 for Peroxide Value,  well below established guidelines for edible oils. Previous PV tests for several Fox Valley products have all tested <5 indicating excellent shelf-stability in terms of very low onset of rancidity in a high-fat content milk powder.


√ Physical characteristics. Powder finely textured, granular, and non-sticky.  Measuring powder by volume or parts rather than weighing continues to cause error rates of + / - 4 to 6% from the calculated average weight of the product. Interestingly, the weight of the powder has steadily increased over the last 10+ years, requiring periodic recalculation of previously used formula recipes. 


√ Reconstitution (wetting and sinking). Very poor performance when correctly adding powder to warm water, with test samples only very minimally submerged in 2 minutes. A full 5 minutes of mechanical dispersal (stirring/whisking) is definitely required to start the reconstitution process.

√ Reconstitution (dispersal and dissolution). Reconstitution is then only completed after an 8-hour resting period from preparation (mixing) to final use (feeding), improving final reconstitution by ≈90%. Without the rest period and quickly prepared for an instant use/feeding, almost 7% of powder remains dry and not fully reconstituted. 

Ingredients (as listed on the package label)


The following table lists the ingredients in Fox Valley 32/40. It seems to have not changed in the last 10 years. As to Primary Ingredients, all fat is provided exclusively from vegetable oil. It is cow milk based for proteins, especially caseins, which is predicted to show poor wetting and sinking during reconstitution. Carbs are provided through the corn syrup solids (glucose), though some lactose is likely supplied through the dried skim milk.

The list of Secondary Ingredients shows many small-quantity additives and supplements for minerals, vitamins, amino acids, and flavorings. 

No fermentation products are included which differentiates Fox Valley from several of the other milk replacers that have begun to add probiotics as well as some prebiotics.

Fox Valley 3240 Ingredient list.jpg

Proximate analysis

The following table shows the results of the proximate analysis performed by the lab as compared to the Guaranteed Analysis (max/mins). The red shaded values indicate where the lab analysis determined that the component concentrations failed to adhere to the maximum or minimum guarantees. 

The table compares the 2022 sample to an average of the last 10 samples tested (from 2021 back to 2019). The most notable difference is a 5 percentage point increase in fat to 40.7% that now adheres to the Guaranteed Analysis. Crude fiber has remained the same, though the source is unclear from the list of ingredients. Metabolizable energy content (ME Kcals) is virtually unchanged, up just slightly to 5.45 kcal/gram of powder, likely due to the increase in fat content.


The 2022 values are now included in the Wildlife Formula Calculator. While only slightly changed, it is advisable to review any existing formula recipes based on the latest information.

Fox valley 3240 proximate analysis.jpg

Ash - dietary minerals

The following table shows the results of the dietary mineral analysis performed by the lab. The table reflects very little change in concentrations of Calcium and Phosphorus. All other dietary macro minerals showed only slight differences. The micro minerals did show some differences, but in such minute concentrations, these could be partly attributed to standard lab testing measurement tolerances.

Fox Valley 3240 Minerals.jpg

Fatty acid profile

The fatty acid profile is shown in the following table, which also confirms that the amount and type of vegetable oil contained in the product have most likely remained unchanged from prior years. It is notable that the Fox Valley 32/40 has a remarkably high concentration of saturated fat relative to other milk replacers. The total saturated fats representin almost 90% of the total fat in the product. The product has a notable concentration of the saturated fats especially in the medium-chain triglycerides of caprylic and capric acids. This would be of significant benefit to a species such as the Eastern cottontail that has a dietary need of a higher concentration of medium chain triglycerides (MCT C:8 - C:12).  

Fox Valley 3240 Fatty Acid Profile.jpg

Peroxide Value (PV) test results

The sample was tested for rancidity, returning a PV (Peroxide Value) of 3 at 142 days after manufacture. This is well within the max Peroxide Value (PV) of <10 for edible oils. Prior samples of 32/40 and other Fox Valley products have consistently tested <5 for PV. Subsequent testing is also needed to determine if Fox Valley 32/40 continues to demonstrate acceptable shelf stability during the quoted 24-month product life span.

Physical characteristics and measurement error [tests performed by WildAgain]

Fox Valley 32/40 continues to demonstrate the characteristic very fine, granular and non-sticky consistency similar to other Fox Valley powdered milk replacers. This is likely a result of absence of a spray-drying manufacturing process. 

Fox Valley 3240 Texture.jpg

Physical characteristics and measurement error [tests performed by WildAgain]

The very fine texture of the powder continues to minimize measurement error challenges when measuring a given amount of powder to include in a formula recipe. However, mixing by parts using a scoop or other volume measure results in measurement error ranging from +4% to -6%, a slight improvement from prior samples tested. Weighing the powder eliminates this unnecessary user induced error, provides for a uniform formula at each mixing and preparation (Mixing Guide), and helps insure consistent nutrition in the formula.

Also of note is the tendency for the product to 'gained weight' over the years, with a slight trend from 2009 to present to a heavier product.

Fox Valley 3240 weights.jpg
Fox Valley 3240 Weight history.jpg

Reconstitution tests - wetting and sinking [tests performed by WildAgain]

The Fox Valley 32/40 sample demonstrated remarkably poor wetting and sinking of the dry powder, being at best only very minimally submerged in the warm water after 5 minutes as shown in the images below. The image at left shows the large amount of undispersed powder. The image at right shows a close-up view a very well defined powder:water interface that has yet to wet. This is presumably due, at least in part, to the casein-rich formulation of this product.   This demonstrates that mechanical mixing would be required to achieve more complete dispersal and reconstitution. The sample was then stirred with a small whisk for 5 minutes until all visible dry clumps were not present.

Fox Valley 3240 Unwetted Powder.jpg

Reconstitution tests - dispersal [tests performed by WildAgain]

The formula was whisked by hand for 5 minutes until all visible dry powder had been determined to be dispersed so no small clumps were visually present – and it appeared smooth, ‘milky’ – and presumed ‘ready to feed.’ The formula was then poured through the stack of sieves, with the largest mesh size on top (500µm). The first image below shows the unwetted powder retained (trapped) by the 500µm sieve when poured immediately after mixing (left image is poured immediately after mixing while the right image is poured after an 8-hour rest in the refrigerator). Both looked smooth and silky. However, once sprayed with water to break the surface tension of the liquid, clumps of unwetted powder became very obvious, even though visually it had appeared that the formula just prepared had been completely mixed and free of any dry powder clumps. The left image a direct pour of the formula right after it was mixed, while the right image is a pour of the formula that had been allowed to rest 8 hours, and then reheated to 110 degrees F. Comparisons shown in these images demonstrates significant improvement (in terms of less unwanted, dry powder) after allowing the formula to simply rest a full 8 hours

Fox Valley Reconstitution Compare 500um sieve.jpg
Fox Valley 3240 Reconstitution Compare Sprayed.jpg

The following image is a close-up of the formula that had been mixed and rested for 8 hours. Prior to the water spray to break the surface tension, the formula appears to be thinner in overall consistency reflecting the benefits of the rest period. This means more of the liquid passed through the 500µm sieve because of a more complete reconstitution. However, as shown, there still remained some small clumps of dry powder, though in less quantity than the formula not afforded the opportunity to rest prior to use.

Fox Valley 3240 Reconstitution Closeup.jpg

The instant mix (no rest sample) showed a surprising and disturbing outcome in the smaller mesh sieve. After removing the 500µm and 250µm sieves from the stack, the 125µm sieve was found to have retained enough unwetted, dry powder to actually obstruct flow of liquid through the sieve. Very little residue was retained in this sieve for the 8-hour rest sample. The images below show the amount of sludge-like residue after spraying with water to break surface tension. The left image is the 'instant-mix' sample with considerable unreconstituted powder remaining, and thick enough to mostly obscure visibility of the lab sink drain under the sieve. The right image shows the 8-hour sample with only minimal unreconstituted power remaining, with the sink drain clearly visible through the fine mesh of the sieve.

Fox Valley 32_40 Residue 125um sieve.jpg

Reconstitution tests - Observed results

When the prepared formula sample of Fox Valley 32/40 was allowed to rest for 8 hours, a 91% improvement in dissolution resulted, with less dry material remaining amounting to less than 1%. The following chart clearly shows the benefit of the 8-hour rest period. This degree of improvement is consistent with other casein-rich powdered milk replacers.​

Following the chart below is a visual presentation of how Fox Valley 32/40 performed in the sieves, comparing the instant mix to the 8-hour rest samples. They are presented in order of the largest mesh sieve to the smallest.

Fox Valley 3240 Recon Efficiency.jpg
Fox Valley 3240 500 sieve.jpg
Fox Valley 3240 250 sieve.jpg
Fox Valley 3240 125 sieve.jpg

"What's it all mean?"


See Part 2 for analysis, discussion and impressions of this new round of testing of Fox Valley 32/40.





Fox Valley 32/40 is manufactured and sold as a substitute powered milk replacer product for use with wildlife.

Product assays performed by the independent lab adhere to the Official Methods of Analysis of AOAC INTERNATIONAL (Association of Official Analytical Chemists) and the Official Methods and Recommended Practices of the AOCS (American Oil Chemists Society).

The authors have no conflicts of interest with the independent lab, or any of the products or manufacturers discussed in this article.

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