Analysis of the Ruminant Digestive Systems – Part 2

Large Ruminants vs. Small Ruminants

By WHITETAIL INSTITUTE STAFF

Pay close attention when you are traveling between Wichita and Emporia, Kansas and you will have a good chance in seeing some very impressive bucks. A few months ago I found myself in this particular part of the country driving up I-35 in the waning hours of an October day. As I typically do at this time of the day, I was glancing at the field edges looking for roving whitetails when I happened to catch movement next to a clump of river side oaks.

Closer scrutiny revealed three or four does along with an impressive 10-pointer browsing on woody brush at the edge of a cattle pasture. Out in the pasture a herd of cows leisurely grazed away at shin-high grass. The image brought my mind back to a conversation I overheard some time ago while visiting with a feed-and-seed store manager.  A customer was standing at the counter talking to one of the employees about purchasing food plot seed and mineral supplements for his deer lease. The conversation went something like this. 

(Customer) “My lease is basically a cattle operation.  Grass pasture, some hay and little row crop. I want to plant a couple food plots but I would guess that the deer are getting all they need. I mean, the farmer knows his stuff about cows and makes sure his pastures, hay and other crops are top notch.” 

(Employee) “Well, you’re right about Bill, he does run a good cattle operation out there.” 

(Customer) “Tell you what, just give me whatever seed Bill is using for his pasture mix or his hay crops and I will plant a couple spots with that.”

Honestly, I could see how this could be a logical thought process. That is if you’re unfamiliar with the differences between large ruminants such as cattle and small ruminants such as deer. Seeing these Kansas whitetails feeding along the woodline while the cattle grazed the tall grass was a perfect example of the differing preferences and needs of small ruminants vs. large ruminants. Undoubtedly, the deer were working on some highly digestible woody browse while the cattle where very content with the mature and somewhat rank grass pasture.

In part one of this series, we learned about the ruminant system, how the various parts function and how the ruminant digestive system works to derive nutrients out of the food stuffs. While all ruminants have the same basic digestive components, there are major differences between large ruminants and small ruminants in terms of food source preference and utilization. In order to put together an effective nutritional management program for deer, it is vital to understand these differences. 

Eating Habits of Deer vs. Large Ruminants

Deer are considered concentrate selectors or sometimes they are referred to as browsers. What this means is that they pick and choose the food sources they consume.  They may even select a certain part of the plant such as the leaf or bud while ignoring the rest of the plant. As we learned from part one, the shape of a deer’s mouth aids in this as it is pointed with a long tongue that enables deer to selectively consume food stuffs. Large ruminants such as cattle on the other hand are considered grazers and are mostly non-selective in their eating behavior. Once again, the muzzle is indicative of this eating behavior being much wider than that of deer. 

The Answer Lies in the Rumen

So why are the eating habits different between small ruminants and large ruminants? The answer to this question can largely be answered with a close examination of the rumen of each classification of animal. First, as you can probably deduce, large ruminants have a much larger rumen than small ruminants. As we discussed in the last issue, the rumen is the “heart” of the ruminant system. This is the part of the digestive system that is responsible for the microbial fermentation and subsequent breakdown of food stuffs consumed by the animal. This “paunch” makes up the largest percentage of the stomach structure and contains millions of microorganisms that live in a synergistic relationship with the animal. When food stuffs enter the rumen, these microorganisms begin to break down the food particles, changing the food composition to useable and digestible components. The difference between large ruminants and small ruminants is the physical size of the rumen sac. 

Large ruminants such as cattle have a rumen many times larger than that of deer. This larger size means more interior rumen surface area along with a larger population of microorganisms. This combination enables large ruminants to utilize harder-to-digest food stuffs, deriving nutrients that small ruminants are unable to. Examples of types of food stuffs include mature vegetation and heavily stemmed forages with high lignin content.

Small ruminants can not efficiently digest heavily stemmed, mature vegetation and therefore are forced to search out vegetative forages. In general, vegetative plants are those that are in the early stages of growth and are pre-bloom or have not reached the reproduction stage of producing seed. Typically, the farther away from seed production a plant is, the more digestible it will be.  Vegetative forages require far less microbial fermentation to extract nutrients and are therefore better suited to a small ruminant like deer. A good example of this is hay-variety alfalfa. If you observe deer usage of an alfalfa hay field you will notice that the largest percentage of feeding occurs when the alfalfa plant is young, maybe less than a foot tall.  As the alfalfa grows, the stem thickens to support weight and the digestibility, especially to small ruminants, decreases. Once it has been mowed and baled, deer again begin using the field heavily as the young, tender shoots begin to emerge. 

The Nutrients

Another major consideration in nutritional management of whitetail deer is nutrient requirements.  In general, small ruminants require a much higher nutrient level percentage in the diet than large ruminants.  This is especially true for deer due to various physiological functions such as antler growth. 

Protein

Protein is the building block of muscle and bone.  Over the years, protein has received a lot of press in the deer world as a vital nutrient for antler growth, doe lactation and fawn development. When you realize that up to 80 percent of a growing antler is protein you know why it is so important. In most cases, cattle require only 12-14 percent protein in the diet. There are some exceptions, such as lactating dairy cattle, but this is a good rule of thumb. Deer on the other hand require 16 percent to 18 percent protein in their diet for optimal antler growth and milk production. It is important to keep in mind that these percentages are for the overall diet. In other words, if a deer consumes a total of eight pounds of food per day, at least 1.28 to 1.44 pounds of this food needs to be protein. Many forms of natural food stuffs are quite low in protein making it vital that forage planted for deer are much higher than the 16 percent to 18 percent needed to create a balance and collectively achieve the desired total protein level.

Couple this with the previously mentioned digestibility needs and it is easy to see why forages for cattle may not work all that well with deer. In fact, this philosophy is reciprocal. Forages designed for deer are often not a very good choice for cattle as they are too high in nutrients and are digested too rapidly in the rumen causing problems such as bloat.

Minerals

As with protein, the mineral requirements for deer are much higher than that of cattle. This has less to do with rumen size than it does with the physiological differences between the species. The yearly production of new bone (antlers) requires a greater need for mineral. Furthermore, the mineral content of deer milk is much higher than that of cow’s milk, making a doe’s mineral requirements higher than that of cows.

So what does all of this have to do with developing a nutritional management program for your deer herd? First, you must take into consideration that deer are small ruminants which requires you to examine your food plot choices wisely. We have learned that small ruminants require a more highly digestible, vegetative food source. In fact, they will search them out, which sheds some light on food source preference. We also have learned that nutrient needs are typically higher for small ruminants.  When taking in these considerations, the characteristics of the forages you select are vital to derive the results you are looking for.

It is this very thinking that is the core to food plot development at the Whitetail Institute. One of the best examples is Imperial Whitetail Clover. Imperial Clover was genetically selected to stay vegetative for a very long period of time and also to be a low seed-producing plant. This combination increases the nutrient content of the plant and at the same time ensures high palatability and attractiveness.

In the third and final issue of this series, we will continue to examine how the deer’s ruminant stomach affects a nutritional management program. Specifically, we will look at rumination and how it affects deer behavior and how it can be used when designing food plots. We will take a deeper look into how food plot selection is affected by the ruminant system as well as how rumen function plays a role in the formulation of nutritional supplements and minerals.

To see the first story in this series see Volume 16 # 3 of the Whitetail News at www.whitetailinstitute.com.