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Zoologic® 33/40 - Part 1. Testing data and comparison to the new Esbilac®

PetAg® manufactures and sells a collection of milk replacer products under the Zoologic® brand name. This line of milk replacers is targeted for use with wildlife species that "...may be used alone or blended with other products in the Milk Matrix family to formulate a milk replacer with nutrient levels that closely match a species' natural milk." This formulation has been widely used by many rehabilitators, zoos, and others around North America since the early 1990's. While the product does not seem to have changed in the past 10+ years, a new round of testing has been conducted with side-by-side comparisons to PetAg®'s Esbilac® which is specifically made for use with puppies, and is also a 33/40 formulation. This article (Part 1) discusses those lab and performance test results, as well as the comparison to Esbilac®. Part 2 discusses and offers suggestions on the recent tests, highlighting similarities and differences between the two products (PDF).

Zoologic Milk Matix 33_40.jpg


Zoologic® 33/40 was tested in conjunction with WildAgain's recent round of in-depth product testing of powdered milk replacers used by wildlife rehabilitators. This product is widely used by small mammal rehabilitators, animal caretakers at zoos, and others in North America. It appears that very little has changed in this product in at least 10 years.

Part 1. This analysis provides the chemical analysis of a 10-month sample (manufactured in 2022) of Zoologic® 33/40. It also provides function testing on some of its formula preparation performance characteristics such as measurement and reconstitution. It does not assess how the product will perform when fed to orphaned wildlife in rehabilitation, though some of the information can certainly be used to help make decisions regarding use of the product. As a reference point, some of the chemical characteristics are compared to recent lots of the product tested during 2019-2021.

Part 2. An accompanying article discusses some of these test results and offers suggestions that wildlife rehabilitators may consider when using Zoologic® 33/40.

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 prebiotics or probiotics are listed, which differentiates it from the new formulation of Esbilac®.

√ Proximate analysis. Concentrations of protein, fat and fiber exceed the expected Guaranteed Analysis values. They are also higher than Esbilac®. The 3.6% of crude fiber is of interest, since there is no discernible source of fiber listed in the ingredients on the label. These higher values resulted in carbs value at 9.3%, about 40% lower than Esbilac®.

√ Ash. Very little has changed with dietary minerals tested from prior samples of Zoologic® 33/40 . The concentrations for calcium and phosphorus are about 10% higher than those found in Esbilac®.

√ Fatty acids. Zoologic® 33/40 has a higher concentration of saturated fats and a corresponding lower concentration of polyunsaturated fat than found in Esbilac®.

√ Rancidity. The 2022 sample tested at a low value of 4.1 for Peroxide Value (PV) at 10 months post-manufacture, well below established guidelines for edible oils. Previous PV tests for Zoologic® lots 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. Zoologic® 33/40 continues to have the characteristic very loose, fluffy and sticky consistency as in prior years, and similar to other PetAg® powdered milk replacers, including the new Esbilac® formulation (2022). Measuring powder by volume or parts rather than weighing continues to cause error rates of +/-  -9 to +4% from the calculated average weight of the product.

√ Reconstitution (dispersal and dissolution). Reconstitution is completed after an 8-hour resting period from time of preparation (mixing) to final use (feeding), improving final reconstitution by ≈87% versus an 'instant mix' without resting time. Without the rest period (and instead quickly prepared for an instant use/feeding), 3% of the powder remains dry and not fully reconstituted.

Ingredients (as listed on the package label)

The following table lists the ingredients in Zoologic® 33/40, which seem to have not changed materially over the last 10 years. As to Primary Ingredients, all fat is provided exclusively from vegetable oil. It is cow milk based for proteins, especially casein, which would normally predict 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. [Interestingly, a label from a 2008 lot indicated egg yolk as a protein source but is now substituted with dried milk protein.]

The list of Secondary Ingredients shows many small-quantity additives and supplements for minerals, vitamins, amino acids and flavorings. Included in the list are mono and diglycerides, maltodextrin, and lecithin as functional components to aid with reconstitution.

Zoologic® 33/40 and Esbilac® appear remarkably similar in formulation, with the exception that Zoologic® 33/40 does not contain the fermentation products for probiotic benefits or the inclusion of powdered cellulose likely intended to provide prebiotic digestive benefits. While Esbilac® (2022) "contains prebiotics + probiotics for healthy immunity and digestion," prebiotics and probiotics are not included in the Zoologic® 33/40 formulation.

Zoologic 3340 Ingredients.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 (GA). The red shaded values indicate where the lab analysis determined that the component concentrations failed to adhere to the minimum or maximum guarantees.

The table compares the 2022 sample to the new Esbilac®. Notably, the concentrations of protein and fat are higher in the Zoologic®. They are also equally higher than the last 6 lots of Zoologic® 33/40 tested during 2019-2021. Because of these higher levels, carbohydrates are correspondingly lower. Crude fiber is remarkably higher at 3.6% versus a GA of 0%, with no source of the fiber indicated from the list of ingredients. Metabolizable energy content (ME Kcals) is virtually unchanged at 5.57 kcal/gram of powder, down slightly from an average of 5.59 kcal/gram from prior lots.

The 2022 values are now included in the Wildlife Formula Calculator. With the protein and fats now testing slightly higher, it is advisable to review any existing formula recipes based on the latest information.

Zoologic 3340 Proximate Analysis.jpg

Ash (dietary minerals)

The following table shows the results of the dietary minerals analysis performed by the lab. The table reflects slightly higher concentrations of Calcium and Phosphorus than for Esbilac®. When compared to prior lots of Zoologic®, mineral concentrations have remained very consistent since at least 2019.

Zoologic 3340 Minerals.jpg

Fatty acid profile

The fatty acid profile is shown in the following table. Zoologic® 33/40 has a higher concentration of saturated fats and a correspondingly lower amount of polyunsaturated fat when compared to Esbilac®. It is notable that the Zoologic® 33/40 has a remarkably higher concentration of saturated fats compared to Esbilac®, especially the C:8 thru C:14 medium chain triglycerides. The higher saturated fats (especially in the medium chain triglycerides of caprylic and capric acids) would be of significant benefit to a species such as the Eastern cottontail, which has a dietary need of a higher concentration of medium chain triglycerides (MCT C:8 - C:12).

Zoologic 3340 Fatty Acids.jpg

Peroxide Value (PV) test results

The sample was tested for rancidity, returning a PV of 4.1 at 307 days after manufacture. This is well within the max PV of <10 for edible oils. Prior samples of Zoologic® 33/40 products have consistently tested <5 for PV. Subsequent testing is also needed to determine if Zoologic® 33/40 continues to demonstrate acceptable shelf stability during the remainder of the quoted 24-month product life span.

Physical characteristics and measurement error [tests performed by WildAgain]

Zoologic® 33/40 continues to have the characteristic very loose, fluffy and sticky consistency as in prior years, and similar to other PetAg® powdered milk replacers, including the new Esbilac® formulation (2022). This is likely a result of the spray-drying manufacturing process. Measuring this type of powder by volume or parts rather than weighing continues to cause error rates of +/-  -9 to +4% from the calculated average weight of the product. Weighing the powder eliminates this unnecessary user-induced error, provides for a uniform formula at each mixing and preparation (Mixing Guide), and helps ensure consistent nutrition in the formula. The bulk dry weight of the product has remained very consistent over the last several years.

Zoologic 3340 Texture.jpg
Zoologic 3340 weights.jpg

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

The Zoologic® 33/40 sample demonstrated remarkably good wetting and sinking of the dry powder, being almost completely submerged in the warm water after 5 minutes as shown in the images below. (The sample appeared totally wet after only 1 minute.) The image at left shows only a very minimal amount of unwetted powder remaining at the surface after 5 minutes. The image at right shows a view beneath the surface where sinking and dispersal is evident. This is somewhat surprising, at least in part, due to the casein-rich formulation of the product. The strong wetting and sinking properties are likely due to the spray drying processing that deforms and creates sponge-like surfaces of the dry milk particles. The clumping below the surface (characteristic of casein-rich powders) demonstrates that mechanical mixing would be required to achieve more complete dispersal and dissolution. The sample was then stirred with a small whisk for 5 minutes until all dry powder and submerged clumps were not visibly present.

Zoologic 3340 Wetting and Sinking.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 sieve on top (500um). The first image below shows the unwetted powder retained (trapped) by the 500um sieve when poured immediately after mixing (left image is poured immediately after mixing looking mostly smooth and silky but with some small clumps apparent). However, once sprayed with water to break the surface tension of the liquid (the image to the right), more clumps of unwetted powder became obvious, even though visually it had appeared that the formula just prepared had been completely mixed and free of any dry powder clumps. The second pair of images is a direct pour of the formula (left image) after it had been allowed to rest 8 hours in the refrigerator, and then reheated to 110 degrees F. The right image is after a quick water spray, showing a significantly smaller amount of unwetted powder remaining. Comparisons shown in these images demonstrates significant improvement (in terms of less, unwetted, dry powder) after allowing the formula to simply rest a full 8 hours.

Zoologic 3340 Inital Pour.jpg
Zoologic 3340 Pour at 8hours.jpg

Reconstitution tests - observed results

When the prepared formula sample of Zoologic® 33/40 was allowed to rest for 8 hours, an 87% improvement in dissolution resulted, with less dry material accounting to only 0.4% of the original amount in the test. 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. The chart also shows the comparison to Esbilac® which also showed significant improvement after an 8-hour rest, yet still resulted in almost 2% of the original powder remaining unwetted and in particle sizes exceeding 125um in size.

Zoologic 3340 Instant Mix Chart Rev.jpg

The following images provide a visual presentation of how Zoologic® 33/40 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.

Zoologic 3340 500um sieve.jpg
Zoologic 3340 250um sieve.jpg
Zoologic 3340 125um sieve.jpg

"What's it all mean?"

See Part 2 for analysis, discussion, and impressions of this new round of testing of Zoologic® 33/40 and comparison to Esbilac®.


Zoologic® 33/40 is manufactured and sold by PetAg® as a part of a family of substitute powdered milk replacer products for use with wild animal species.

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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