Dietary Minerals - Overview


Why all the attention on minerals in milk replacers?


Dietary minerals are inorganic elements that are essential parts of any diet – including mother’s milk and substitute formulas fed to young mammals. Some, like calcium and phosphorus, are more well-known and more abundant in the body.  Other minerals, defined as “trace” minerals (such as manganese, copper, and zinc) are found in smaller amounts in the body.  They may be less familiar, but they too have key functions. While there is some information on the functions, roles, importance, amounts, interactions, balances, etc. of these trace minerals, much of the knowledge is limited and evolving as it pertains to human and a few domesticated species. There are even more unknowns about their role with wild mammals, which display anatomical and nutritional differences (e.g., herbivores vs carnivores, marsupials vs eutherians, monogastric omnivores vs hindgut fermenters).


Acknowledging there are unknowns, it is still useful to consider the role of minerals in the milk replacer formulas being fed to wild mammal babies in rehab. This section provides some very introductory information. It is up to the reader to learn more and consider how the information applies to wild mammals in care – and to their formulas.


1) It cannot be overstated that while minerals are known to be essential to health – and diet - there is still much to learn.


2) There continue to be questions about the mineral amounts/balance needed for humans, especially infants, and even more for other species.


3) In addition to the presence and amounts of these minerals is the importance of “bioavailability.” This refers to the degree of digestion, absorption and utilization – or to what extent are these minerals usable to the body.  Bioavailability can vary depending on the species, age and health of the animal.


It also should be noted that formulas commercially produced for human infants tend to contain larger amounts of those minerals than does human breastmilk. One suspects that manufacturers trying to include the appropriate range of minerals may add slightly larger amounts due to the lower  bioavailability in manufactured formula.


Many publications describe how foods manufactured for animals (including milk replacer products) tend to be lower in quality, which can include decreased digestibility.  So it seems useful to review quality, amounts, and types of minerals used in milk replacers for animals. This includes individual products and lots produced currently, as well as trends over time.


The term "ash" is used throughout this website, included on many nutrient composition test analysis, and even appears on food product labeling. It refers in general terms to the “mineral content of a food product.” When measuring mineral content, a sample of the product is burned at a high enough temperature to quickly and completely oxidize all protein, fat, carbohydrates and fiber. Since elemental minerals do not burn, what is left is their "ash." The residue is then analyzed for its specific mineral/elemental content. The body accomplishes this same oxidation through healthy metabolism, though over a much slower time period.


What minerals are tested in milk replacer powders?


There are many minerals that can be tested in milk powders. WildAgain made a decision to use the proximate analysis for milk composition that included the select minerals highlighted at the top of the page, since those elements could have a significant effect on growing mammals (click on any of the minerals in the header of this page to learn more about each one). ALL of the vitamins/minerals present in the milk powders were not tested because it is difficult to know if the amount reported is appropriate, how it would be balanced with other minerals, or to determine bioavailability. Reviewing and analyzing results of tests on select minerals in the milk replacers conducted over 10+ years offer some clues about the levels and ranges. It is also essential to consider the health and growth of the animals consuming the products in assessing the product’s performance, or if there are concerns.


Standard Reference Material (SRM) 1549 Nonfat milk powder from the National Institute of Standards and Technology is intended primarily for use by scientists in calibrating instrumentation and evaluating the reliability of analytical methods for the determination of constituents in milk, milk powders, and other biological matrices. The SRM1549 sample data is for 100 grams. It includes a table (at right) from the Certificate of Analysis for concentrations of the macro and micro minerals used as reference points in powdered milk. The macro minerals are displayed in concentrations (by % of total) and the micro minerals are shown in concentrations (as parts per million (mg/kg)).


It must also be noted that manufacturers may change mineral composition of food products. For example, they may do so: (1) if new information suggests a benefit of changing the amount or balance of a mineral to a different level; (2) to provide a more bioavailable form; (3) due to a change in their manufacturing method; (4) potential concerns. These changes could affect the mineral amounts, which may or may not affect the ability of the animal to effectively absorb/digest it.


This reinforces the importance of regularly monitoring the animal’s health. It is helpful to become familiar with conditions related to deficiencies or excesses of particular minerals. That is challenging since many of the symptoms can be rather general and may be caused by a large variety of factors related to diet and other conditions. Plus, it can be very difficult to note subtle differences with various species and ages, especially tiny animals (e.g., weighing less than 25 grams).  In some cases, the caregiver may not be able to specify the change or potential problem, other than, “Something doesn’t seem quite right/normal – even if I don’t know exactly how.” Those can be useful early clues that can help identify patterns or potential problems and decide on further steps (e.g., closer monitoring, consultation) or if/when any changes might be required.


Mineral deficiencies and excesses - examples of what to look for and how to make an initial assessment


Since calcium is one of the most well-known minerals, let’s start with it. Some believe that a calcium deficiency would be instantly obvious. However, calcium deficiencies develop gradually – and do not show immediate or obvious signs. More obvious symptoms are more likely when the calcium reaches very low levels (hypocalcemia), including fatigue, stiff and spasming muscles, skin problems, thin bones that fracture without trauma, seizures. Care must be taken with diagnosis and case-taking (including diet history), since those same symptoms can be a result of other conditions and causes – and need other treatments.


Often when an animal displays mobility or bone-related issues, it is assumed to be directly related to a calcium deficiency. However, it is important to still consider other potential conditions and causes, rather than immediately providing supplemental calcium, which could inadvertently lead to consuming TOO MUCH calcium (hypercalcemia). This can result in lethargy, fatigue, gastrointestinal problems, cardiac irregularities, muscle weakness, and possibly bone weakness. Plus, too much calcium also can reduce or even prevent the absorption of phosphorus – which can affect bone growth. Such considerations must always be considered supplementation treatment plan is undertaken.


Deficiencies or excessive amounts of calcium can present issues, as well as cause imbalances with other minerals resulting in further complications. Magnesium and Vitamin D also play key roles with calcium and phosphorus.


Thus it is absolutely essential that decisions to adjust calcium levels be made with a complete knowledge of the species and patient and the nutritional needs, including the amounts needed and the degree of digestibility.  Errors in supplementation can pose serious and potentially fatal risks for the animal. While a few may have considered popular antacids that are easily available ‘over the counter’ as a possible form of calcium supplementation, they may potentially result in toxic concentrations if not prescribed, administered and monitored closely. Check multiple professional sources, ask questions, consider risks and apply caution when making decisions choosing and using any calcium supplements, even those commonly designed for and used with humans.


Phosphorus is another of the better-known minerals in the body. If phosphorus levels get too low (hypophosphatemia), fatigue and low energy can result, as well as muscle weakness. In addition, those with low phosphorus may have kidney issues and poor gastrointestinal absorption. A phosphorus deficiency that occurs concurrent with low levels of calcium and vitamin D can further result in skeletal weakness and pain, ataxia, anemia, and increased risk of infection. Again, since such conditions can be caused by various factors, it can be challenging to determine if a phosphorus deficiency may be involved.


An excess of phosphorus (hyperphosphatemia) can also cause issues, which can be variable.  Some patients might not show symptoms, while others may actually exhibit symptoms similar to those with LOW phosphorus, including joint and muscle pain, muscle weakness. Since the public may feed some wild animals a proportionately large amount of foods such as seeds and nuts that are high in phosphorus, it is not uncommon for rehabilitators to admit animals with phosphorus levels approaching toxicity. So again, the caregiver and veterinarian need to consider the symptoms and background (including diet history), and carefully decide on next steps – which could be adjusting diet rather than or in conjunction with administering any supplement or medication.


What about trying to change mineral levels, especially through supplementation?


It is very difficult to know exactly what mineral levels are needed for a species and age of wild mammal, as that data is not readily available. Without that information, many questions arise: (1) What is the target range for the species and age? (2) What level of the mineral does the animal have already? (3) How was it tested and is that test accurate? (4) What is the mineral type, quality, amount, size, and so forth since there are many variations? (5) What is the bioavailability of the mineral in the food? The list of questions can be quite extensive.


Revisiting the calcium deficiency example discussed above, the first step would be a veterinary consultation. 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 level 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.


Trying to adjust the mineral level for the animal can mean inadvertently giving it too much or little. Giving an inappropriate amount or type of a mineral can cause serious and even life threatening problems – some of which are not reversible. In such cases, the minerals are being used to treat a health condition, that is as a  ‘medicine.’  While many mineral supplements are easily available ‘over the counter’ does not mean they should be underestimated or used without extensive knowledge of the product, benefits, risks, etc. for the species and ages of the patients.


Keep studying...


There are many resources available as you seek further information. If you want to know more about a specific dietary mineral, click on the element symbol on the top of this page. These links to additional pages provide a brief overview  for each mineral, it's health benefits, a brief mention about deficiencies and excesses. They also provide links and resources for further study.




Certificate of Analysis for Standard Reference Material ®1549 Nonfat Milk Powder (National Institute of Standards and Technology - US Dept of Commerce)



Click on any of the minerals above for more info


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