Mineral/Vitamin Supplementation

IT’S JUST COMMON SENSE

PART II

By WHITETAIL INSTITUTE STAFF

Some may think that common sense in today’s day and age is a rare occurring phenomenon. In fact, it is arguable that common sense should be put on the endangered species list. 

In Part I of this series, we discussed both the use and the non-use of common sense in terms of mineral/vitamin supplementation in deer. If you missed our last issue, I will briefly recap the discussion. 

There are two rules of thought in the use of mineral/vitamin supplementation in white-tailed deer management. One camp states that mineral/vitamin supplementation is a valuable, if not vital, tool in improving antler growth, doe lactation, fawn growth and overall herd health. The other camp states that there is not enough scientific data to conclusively surmise that mineral/vitamin supplementation can be used to positively affect the characteristics previously stated. In the first part of this series, we focused on how deer use minerals and vitamins in relation to antler growth, doe lactation, fawn growth and overall herd health. 

For instance, we pointed out the fact that antlers are comprised of approximately 55 percent mineral.  This alone is a strong argument for the importance of mineral supplementation. We also discussed the functions of specific minerals and vitamins such as copper, which is vital in the production of the protein found in antlers and vitamin D, which is involved in calcium transport. The summary of Part I was that minerals and vitamins are needed in large amounts in various phases in a deer’s yearly cycle. Common sense thinking is that supplementing your deer herd with needed minerals and vitamins could do nothing but help all deer reach their genetic potential. 

PART II

As we previously stated, the main argument of those doubting the importance of mineral/vitamin supplementation in whitetails is that not enough scientific data has been accumulated to prove an actual need. The reason for this stems from the difficulty in conducting conclusive experiments on wild deer. In order to determine nutrient requirements, there must be two groups of deer each eating the exact same diet. Then in one group (test group) the nutrient being tested is altered up or down, while the other group (control group) remains on the same diet. All of the animals are fed these diets for a particular period of time and then tested for differences in characteristics such as antler growth, body weight, etc. 

The test is done over and over using differing levels of the nutrients until an optimal level is found. As you can probably already see, conducting a test such as this on free ranging, wild whitetails is nearly impossible. First, deer have access to other food sources, which might or might not contain the nutrient being tested. Furthermore, many other variables are present in the wild, which may skew the test results. So in a nutshell, if we can’t scientifically test it, then how will we know conclusively the effects of mineral/vitamin supplementation. 

However, to say that there has been no scientific research showing a difference in deer that consume high levels of minerals, compared to deer that consume low levels of minerals, is not exactly accurate.  For instance, a classic study done at Penn State University showed a difference in body weights in yearling bucks fed two different levels of phosphorus. In this study, yearling bucks that were fed a higher level of phosphorus had higher body weights than those fed a lower level. In all fairness, the deer tested were penned deer and may have been deficient in other nutrients, but regardless, phosphorus was the only difference in the diets. 

Another research project conducted in Mississippi looked at the correlation between high levels of mineral in the soil and body size. Again, soils with higher levels of mineral in the soil (thus higher mineral in the diet) showed a strong correlation to deer with higher body weights. There is typically a strong correlation between higher body weights and larger antler size.

Another approach to looking at nutritional requirements for deer involves the use of data from research done on other similar animals. A common animal used is dairy cattle.  Before I go any farther however, I want to make an emphatic point. Deer should not be considered identical to cattle in terms of nutrition. They are both ruminants (four chambered stomach) but there are great differences between the two in eating habits, ability to efficiently digest various forages, etc.

First, deer are browsers or concentrate selectors, which means they will eat specific plants or specific parts of plants. Dairy cattle on the other hand are grazers, which means they, for the most part, non-selectively consume vegetation. This vegetation may vary from high quality to low quality, but cattle have the ability to digest a wide variety of vegetation. They have the ability to do this because of the large compartment in their stomach called the rumen.

Deer also have a rumen, but compared to cattle, their rumen is much smaller. It is the rumen that contains the microbial colonies that ferment the vegetation and allow the animal to use the nutrients found in the vegetation. The larger the rumen, the greater ability to digest a wide variation of forages, even poor quality forages. Deer, having a smaller rumen, “select” the more highly digestible food sources. 

That being said, the actual digestive function of the two animals is very similar. Though little research has been done on the mineral requirements for deer, extensive research has been done on dairy cattle. There have been literally hundreds of experiments done to determine the optimum mineral requirements of dairy cattle. For instance, the calcium requirement in a lactating dairy cow is approximately 60 percent to 80 percent compared to a non-lactating cow, which requires 40 percent.

During lactation, dairy cows are supplemented with minerals and vitamins to compensate for the increased requirement. Even brood cows producing less milk than dairy cattle are often fed a free choice mineral to improve milk production. When it comes to hardened antlers, a high level of calcium is also present, about 22 percent.

Common sense says that if cattle have increased milk production when supplemented with minerals and vitamins, deer would have increased antler growth and increased lactation when supplemented with a free-choice mineral/vitamin supplement.  Theoretically, both bucks and does require higher amounts of minerals and vitamins than cattle for optimal production. Obviously, antlers are much higher in mineral than cow’s milk, and doe milk has been found to be much higher in nutrients than cow milk. 

Yet another common sense theory is that deer would benefit more from mineral/vitamin supplementation than cattle due to the fact that cattle have a greater ability to digest forage and extract nutrients. Again, based on the larger rumen, cattle have the ability to extract nutrients (minerals/vitamins) out of poor quality forages where deer do not have the ability to the same extent.