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Calcium (Ca) in Powdered Milk Replacers


Dietary considerations 


Calcium is one of the more commonly known minerals in the body - and considered essential for bones. Similarly, when wildlife rehabilitators talk about calcium, they seem to focus almost completely on its role in bones.  This makes sense, since calcium is the most abundant mineral in the body, and 99% of calcium is stored in bones and teeth. However, calcium's role is far broader than that, since almost every cell in the body uses calcium in some way. Calcium is essential for many functions: blood circulation and clotting, muscle contraction (including heart rhythm), nerve impulse, fluid balance within cells, and more. Calcium is also an essential part of the mother animal’s milk for her growing offspring. The calcium in her milk is provided in the appropriate amount to be in balance with the other minerals. All the minerals in her milk are produced in an easily digestible form, necessary for an immature and developing digestive tract.


During rehabilitation, young suckling mammals obtain the calcium in the milk replacer formulas and also later in solid foods during weaning. Both of the manufacturers of such milk powders AND rehabilitators work to keep the amount of the calcium at an appropriate amount, as well in balance with other minerals, such as phosphorus and magnesium. In addition to being in an appropriate amount or concentration, the calcium needs to be in a form and quality that is digestible and utilizable by the animals.


Calcium concentration imbalances


Hypocalcemia is defined as “low levels of calcium in the blood.”  While a mild calcium deficiency may not show obvious signs, a more severe calcium deficiency will likely result in symptoms such as fatigue, stiff and spasming muscles, skin problems, thin bones that fracture without trauma, and seizures. Most rehabilitators are aware of cases when a wild animal has developed health problems directly related to a calcium deficiency, often after being fed a diet too low in calcium.


After receiving a diagnosis, a treatment plan could be implemented that may include supplemental calcium, depending on the cause and the severity of the case. The amount and type of calcium must be carefully selected for the species and age of the animal. Other factors must also be considered, such as digestibility of the calcium. For example, calcium carbonate is more readily available, less expensive, and has a higher concentration of elemental calcium, but is more difficult to digest and may result in digestive disorders. Calcium citrate is easier to digest but is more expensive and has less elemental calcium.  Liquid calcium glubionate has both a high level of elemental calcium and is easily digested, but it is expensive and extremely difficult to find.


On the other hand, there also are cases when an animal may consume too much calcium (hypercalecemia) – which can result in lethargy, fatigue, gastrointestinal problems, cardiac irregularities, muscle weakness, and possibly bone weakness.  Too much calcium can also inhibit the absorption of phosphorus.  And since both calcium AND phosphorus are necessary for bone growth, too much calcium can be as damaging to bones as too little.


Deficient or excessive amounts of calcium can present issues, as well as cause imbalances with other minerals, resulting in further complications. Vitamin D also plays a key role in both calcium and phosphorus absorption. Thus it is absolutely essential that decisions to adjust calcium levels be made with both a complete knowledge of: (1) the nutritional needs of the species, (2) the appropriate amounts of calcium needed, (3) the digestibility of the calcium, (4) the balance needed with the other minerals.  Errors in supplementation can pose serious and potentially fatal risks for the animal.  Some rehabilitators may have considered popular antacids that are easily available ‘over the counter’ as a possible form of calcium supplementation. Be aware that they can potentially result in toxic concentrations if not prescribed, administered, and monitored closely. Check multiple professional sources, ask questions, consider risks, and use caution when making decisions choosing and using any calcium supplements, even those commonly designed for and used in humans.


In the past, many rehabilitators have relied on the manufacturers to provide milk powders with appropriate calcium amounts (concentrations). They also depended on the calcium being produced in a form that is digestible in very young animals, for which the milk powder is produced. The chart below shows that calcium levels have varied in concentration levels in some milk powders over the last 10+ years, based on independent lab tests. However, these tests do not address the animal’s digestibility of the calcium – reinforcing the notion that chemical concentration levels viewed in a vacuum may be misleading. Nor does the chart include the critical calcium phosphorus ratio. Due to these variables and unknowns, it would be prudent for rehabilitators to (1) continue to learn about the products they are using, (2) take note if the animal’s health could suggest any issues with calcium levels, and (3) use caution when considering any supplemental calcium. It is also important to remember that around 2/3rds of the calcium in the milk replacer is bound up in the casein protein molecule as amorphous calcium phosphate. However, it only becomes available once the dried casein is fully reconstituted. Following the complete reconstitution process is critical, as described here. See a list of references and further reading below the chart.


Since the correct range of concentration values for all species are different, and since wild species milk composition is very limited, reference values for whole and lowfat dry milk are provided in the chart.


Since averages can at times be misleading, a closer look at a few of the products where multiple test values are available between time periods, can reveal how the concentration values may have changed over time. Then if those changes are significant, either increase or decrease, the reader may want to focus on the most recent profile of the product. 


Even though some of the changes reflected below may be significant over time, simply trying to adjust with supplements requires considerable knowledge and has the potential to worsen an adverse situation. Please review the section on mineral supplementation in the minerals overview.

Calcium changes over time.jpg

References and further reading (not intended as an exhaustive list)


Brown, Susan. 2014. Key Minerals for Bone Health. Bone Nutrition. July.


Cashman, Kevin and Albert Flynn. 1999. Optimum Nutrition: Calcium, Manganese, and Phosphorus. Proceedings of the Nutrition Society. V. 58, pp. 477-487.


Fowler, M.E. 1986. Metabolic Bone Disease. Zoo and Wild Animal Medicine, 2nd ed. M.E. Fowler, ed. Saunders Co. Philadelphia, PA.

Inzucchi, Silvio. 2015. Understanding hypercalcemia: its metabolic basis, signs and symptoms.  Journal of Postgraduate Medicine. V. 115 (4) pp. 69-76. 


McRuer, David, and Kenneth Jones. 2009. Behavioral and Nutritional Aspects of the Virginian Opossum (Didelphis virginiana). Veterinary Clinics of North America: Exotic Animal Practice. V. 12 (2), pp 217-236.


McRuer, David. 2011. My My Don’t You Have Squishy Bones: Metabolic Bone Disease: Preventing and Treating this Syndrome in Wildlife Patients. Wildlife Center of Virginia. Presentation handout.


Moe, Sharon. 2008. Disorders Involving Calcium, Phosphorus, and Magnesium. Primary Care. V. 35(2) pp 215-vi. 


Murname, Robert. 2002. Common Nutritional Disorders of Wildlife. NWRA Principles of Wildlife Rehabilitation, 2nd Ed. Adele Moore and Sally Joosten, ed. National Wildlife Rehabilitators Association, St. Cloud, MN.

The information included on this website for dietary minerals is extremely narrow in its scope and nature. It is limited to certain charts and graphs displaying content values (% of total) of various powdered milk replacers as tested by an independent chemical lab. Extremely brief overview information is provided as to the primary nutritional and medical benefits of each mineral, as well as a limited discussion of issues that may arise from concentration levels in the body that may be considered deficit or toxic. Entire textbooks on dietary minerals are written for the medical and veterinary professions, in addition to the internet providing ready access to both scholarly and popular literature. Some of those references are included above.


The data values presented above only represent the test values for the presence and concentration of the mineral conducted according to standard chemical testing methods in a controlled laboratory setting. Any point test value is accompanied by a measurement uncertainty range of +/-20%. The concentration values are in no measure an indication of how much of the mineral may be provided to an animal in reconstituted formula or its bioavailability (its degree of digestibility, absorption, or ultimate utilization). Additionally, no testing was performed as to the source of the mineral in the product (such as inorganic salts) or the grade of any added supplements containing the mineral.


What the data can do is inform the reader as to (1) concentration levels in a product as most recently tested (2) changes over time and between lots, and (3) comparisons of relative concentration levels between products. It is merely data that may serve as a starting point when deciding on a milk replacer product(s) and a recipe, or information to consider if certain medical symptoms appear that could be a result of absence or excess of a specific mineral in the formula. The reader is encouraged to consult veterinary or nutritional professionals prior to providing additional supplementation of any mineral.

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