Many popular beliefs are being dramatically changed through scientific discovery. Even in the deer world, we are continuously finding out that what we thought was fact one day is completely disproved the next.
By Matt Harper
For example, for many years it was commonly accepted that adult bucks were doing all or most of the breeding. Recent studies have shown that while adult bucks indeed do quite a bit of the breeding, bucks as young as 1½ are also siring a percentage of the annual fawn crop.
For several years now, I have been formulating free-choice minerals for wild deer. When formulating minerals or any feed product, the vital elements include the ingredients used along with the percentage of those ingredients and the resulting percentage of actual nutrients (calcium, phosphorus, zinc, etc.). But another important factor is nearly always overlooked by people who use free-choice minerals. This final piece of the puzzle is daily intake.
Where to Begin?
Ingredient levels and nutrient percentages don’t mean much if you don’t know how much of the product is being consumed by the deer herd. Free-choice minerals are probably one of the most difficult products on which to get a good sense of intake. There is little to no research on the subject as it pertains to white-tailed deer. You might go to your mineral site and see that it has been pawed at or dug out and little mineral is visible, but it is hard to tell how much was actually eaten, how much leached into the soil, and how much was just mixed in but is now indiscernible from the soil.
Three summers ago I was developing a new mineral product and was constantly frustrated that I didn’t know what the expected intake would be. The most common intake claim by deer products on the market is 1 to 2 ounces per deer per day, or 1/16 to 1/8 of a pound. I struggled with that, because many cattle minerals have a known intake consumption of 2 to 4 ounces per animal per day.
Because intake is typically relative to body weight, one would think that if a cow weighing 1,400 pounds was eating 2-4 ounces of mineral, then a deer weighing 200 pounds should only eat between 0.28 to 0.57 ounces, not 1 to 2 ounces. Now consider that a 200-pound deer is a pretty big deer in most parts of the country, and that does might average 150 pounds. That means their expected consumption should be 0.21 to 0.42 ounces per head per day.
Of course, while mulling this in my Excel spreadsheet I was making a lot of assumptions, so I decided to conduct a research project on one of my farms to see if I could come up with a number based on real data.
Importance of Knowing Intake
As previously mentioned, intake is a vital factor when formulating a mineral or protein supplement or complete feed. Nutrient levels mean virtually nothing if you do not at least have an approximate idea of how much of a product the deer are consuming.
For example, research has shown that a buck needs about an 18 percent protein diet during the antler-growing cycle to maximize antler growth. Deer will consume anywhere between 1 percent to 5 percent of their body weight each day, depending on the time of year, with winter consumption being on the low end of the scale and summer consumption on the higher end.
So, if we take a 200-pound buck and say he is eating 4 percent of his body weight each day, this equates to 8 pounds of total daily food consumption. Now, back to the 18 percent protein. If a buck consumes 8 pounds of total food per day, in order to hit an 18 percent protein level in his diet he would need to consume 1.44 pounds of protein.
Consider two different protein supplements, one with a level of 28 percent protein and one at 22 percent protein. In order to hit the 1.44 pounds of protein, the buck would need to consume 5.1 pounds of the 28 percent product or 6.5 pounds of the 22 percent product. If the buck only consumes 3 pounds of the 28 percent protein product but eats 5 pounds of the 22 percent product, he is actually getting more protein from the 22 percent product than the 28 percent product. Most folks would simply look at the tag, see the 22 percent and 28 percent numbers and just assume the deer is getting more protein from the latter.
Even though we used protein in this example, the same is true for nutrients in a mineral supplement. If one mineral supplement has 5 percent calcium and another has 7 percent calcium, but the deer consumes twice the amount of the 5 percent product, the deer actually is getting more calcium than from the 7 percent product. This is why knowing your intake is so important for your mineral program.
Factors Affecting Mineral Intake
Wild deer are finicky eaters, especially with supplemental products. Any one of a hundred things can influence how often a deer will use a supplemental mineral and how much it will consume. The form it is in (block versus granular), location of the mineral site, soil type, salt content, competition, aggression of other deer, how long the site has been established and a host of other factors all affect how much a mineral site will be used.
Over the years, with the use of thousands of trail camera photos and a lot of trial and error, I have determined a few factors that can influence mineral consumption both positively and negatively on wild deer. I group these into two categories.
1. Non-Nutritional Factors
Location is critical when using any type of mineral. Deer prefer mineral sites that are in cover as opposed to out in the open.
When creating sites, I try to find heavily used trails or trail crossings somewhere in cover (brush or timber) and create the site just off that trail or crossing. This does not guarantee deer will use the site. I have used the same product in sites literally 100 yards apart from each other, and deer heavily used one site but not the other. So when I am creating new sites, I try several locations and replenish the ones that receive continued use, while abandoning the sites with little or no use. Basically, the deer will tell you where they like to eat.
I have also found that — unless there are major changes in the vicinity of the site (i.e. logging, flooding) — a mineral site will receive increased usage with each progressive year. Research has shown that after a site is used, it will often become a part of the feeding and movement pattern. Also, fawns will learn mineral site areas from their mothers and will return to sites even after they are weaned.
Granular minerals seem to work better than blocks, as most of the usage of blocks occurs in the surrounding dirt as the minerals leach into the soil. Along those same lines, deer will more readily utilize minerals that are ground applied than offered in a manmade feeder. Increased aggression by certain deer (usually adult does) that “guard” the site will decrease the number of deer utilizing that particular location. Because of this, I normally recommend at least one site per 40 acres to minimize site competition, with more sites needed in areas with higher deer density.
Soil type is one final consideration for non-nutritional factors. Mineral sites located in sandy areas are utilized less than mineral sites in heavier soils. I cannot definitely answer why this is, but I would theorize that it has to do with excessive leaching in sandy soils or possibly even the gritty nature of sand.
2. Nutritional Factors
Nutritional consumption factors revolve around the attractant agent in the product. Salt is the most common attractant used in mineral supplements. Attraction to salt is caused by the balance of potassium and sodium in the deer’s body. Potassium and sodium must maintain a balance at a cellular level, and since most green, growing vegetation is much higher in potassium than sodium, deer become “salt hungry” during spring and summer as their bodies crave more sodium.
However, salt also can be an intake limiter for the same reason and often is used in livestock minerals to limit intake. So a product that is very high in salt will likely have less total consumption. However, there must be enough salt in the product to help attract deer.
As you can see, getting the right salt level in a mineral can be tricky. As autumn approaches, potassium levels decrease in maturing vegetation. Salt becomes less of an attractant, which means in order to get continued mineral consumption, a different type of attractant must be used.
The Research Project
The methodology I used in my research project was relatively simple. The test involved comparing a beginning mineral weight to an ending weight. But I also had to know how many deer, on average, were using the site each day and if it was simply the same deer returning to site multiple times a day. Also, I had to make sure I didn’t lose any mineral to leaching.
I began the project by placing black plastic feeding pans at my oldest and most frequented mineral sites. I buried them partially in the ground in an attempt to minimize the negative effect of using a container versus the normal method of direct ground application. Also, slightly burying the pan helped ensure the mineral would not be spilled. Cameras were placed at each site to monitor usage. Before beginning the test, I allowed 30 days to let the deer get used to the feeding pan and then began the test after I started seeing consistent usage on my trail cameras.
When I believed the deer were using the site normally again, I removed all content from each pan and replaced it with exactly 5 pounds of mineral at each site. I then allowed the deer to use the sites for seven days, at which time I removed the remaining contents from the pan and weighed it to get a total usage. At the same time, I reviewed the cameras located at each spot to identify how many deer were using the site each day.
While I could identify many of the deer that used the site daily, some did not use the site each day, and some could not be definitely identified as a daily user. Therefore, I took the total number of deer that used the site over a seven-day period and divided it by seven days to reach an approximate number of deer using the site each day. I replicated the test on three different farms to help alleviate variables, at least to a certain degree. The test was conducted in July.
Farm A had an average number of 11 adult deer using the site on a daily basis. At least eight were using the site each day, including three yearling does, two adult does, two yearling bucks and one 3-year-old buck. The amount of mineral remaining in the feeding pan was 3.6 pounds, or 57.75 ounces. This equated to an average ounce-per-head-per-day intake of .289 ounces.
Farm B had a eight adult deer using the site, five of which used the site on a daily basis. The feeding pan had 4.265 pounds, or 68.24 ounces, of mineral remaining. This equated to a .21 ounce-per-head-per-day intake.
The third site on Farm C was discarded due to a camera failure.
Years Site Had Been Used — 12
Initial Mineral Weight — 5 pounds (80 ounces)
Average # of Deer Visiting the Site Daily — 11
Final Weight — 3.6 pounds (57.75 ounces)
Average per head per day intake — .289 oz
Years Site Had Been Used — 8
Initial Mineral Weight — 5 pounds (80 ounces)
Average # of Deer Visiting the Site Daily — 8
Final Weight — 4.265 pounds (68.24 ounces)
Avg per head per day intake — .21 ounces
It would appear that, based on the test results, intake of a free-choice mineral is substantially lower than what is commonly thought and much closer to the predicted intake based on body weight calculation. This being said, many variables are at play and these results certainly do not provide a definite answer.
For instance, did the cameras trigger each time a deer was using the site? In terms of trying to identify the total number of different deer using each site how much did human error play into the results? In other words, were some deer that came to the site twice a day actually counted as two different deer?
Arguably, the test might only be representative for the particular mineral I was using, and a different mineral with different salt levels or other attractants might have shown a different result. However, the formula I used for this mineral is fairly standard and used in many deer mineral products. Also, the use of a foreign object, the plastic feeding pan, could have decreased usage even though I did not start the test until the deer were regularly using the site with the feeding pan in place.
Even taking all of this into consideration, I believe that, at the very least, the results strongly suggest that the intake of free choice minerals is substantially lower than 1-2 ounces per head per day.
OK, even though I think this is pretty cool stuff, you might be asking why this really matters. If you are not formulating your own products, that’s a very valid question.
However, if you are using mineral supplements or considering using them to improve the nutritional plain of the deer herd on your property, I think having at least an idea of the expected intake is important.
As long as you have an idea of how many deer are on your property, knowing expected intake can help you figure out how much mineral you can expect to use each year. Also, if you are not getting at least the intake level of .2 to .4 ounce per head per day, then maybe you need to switch products, move the mineral site or make some other changes to make sure the deer are consuming the desired amount.
There is little question that increased mineral nutrition can improve your deer herd. Now that you know what to expect for intake, you can use this information to make sure your mineral product is performing as it should.
D&DH field editor Matt Harper is a deer nutrition specialist from Iowa.