Planning Habitat for Whitetail Nutrition
A Tour of the Rumen
First, a primer in deer physiology. Deer are ruminants — animals with chambered stomachs that regurgitate and chew “cud.” All ruminants are prey animals, and the rumen is an adaptation that allows them to hide from predators. Ruminants can tank up on food quickly without even chewing thoroughly then retreat to some nasty patch of cover to hide and chew the cud.
Most of us know that deer have a stomach with four compartments. The first compartment is the rumen, and it is the largest. In the deer woods some hunters refer to this as the paunch. If you open the paunch, the odor you smell is caused by volatile fatty acids, the byproduct of rumen fermentation. More on that shortly. Opening the rumen reveals some interesting things and should be part of the field-dressing procedure, though you are better off examining the inside of the rumen after you have removed it from the carcass! You are in the right place if you notice the lining of the rumen, which looks a little like shag carpet. The rumen is smooth on the outside but is lined with thousands of alveoli, which look like little fleshy fingers.
In reality, deer cannot digest browse material any better than you or I. But, the rumen serves as a large fermentation vat that is powered by the vast population of bacteria and other organisms that live there — a vital symbiotic relationship between deer and these microorganisms. These rumen bugs have an ideal environment in which to operate. It is dark, wet, warm, and there is no oxygen present. They go to work breaking down the fiber and other components of a deer’s diet. The deer has adapted to absorb some of the byproducts of this fermentation — those volatile fatty acids mentioned earlier — directly through the rumen wall into the bloodstream, where they are utilized as an energy source. This is a physiological difference between single-stomached animals and ruminants. While the bacteria work on the forage and break it down to more digestible material, they grow and multiply. When you open a rumen, the contents appear to be a well-mixed soup, but actually rumen contents stratify — liquid in the bottom, a fiber mat of feed material floating in the middle and gas space on top. A lot of gas is produced by the bacterial action, which the deer belches away throughout the day. A ruminant that cannot belch will quickly bloat and die. This mass of stuff is continually stirred by rumen contractions — the rumen is a big muscular bag, actually.
The second compartment is called the reticulum, and it serves as a screen which only allows smaller particles to wash on through to the true stomach in liquid form, along with millions of bacteria. The bacteria themselves become an ideal source of protein for the deer. Bulky, fluffy material in need of further digestion stays behind in the rumen to be re-chewed as the deer’s cud. As fiber is digested away, the particles are less buoyant and tend to sink down through the mass and through the reticulum, and down to the true stomach, called the abomasum, and intestine. In a sense, deer farm the rumen, using the bugs the same way we use livestock — to upgrade the nutrition of plant materials for our own nutrition.
Now let’s think about what happens when a deer eats lush clover from the field outside my office window. This material is highly digestible and does not stay in the rumen very long. The deer gets a large dose of nutrients, and the quick passage time makes room for more food to be eaten soon. Contrast this clover to a wad of mature orchardgrass stems, if you could get a deer to eat such a thing. What happens to this in the rumen? The bacteria require a lot more time to break down this high-fiber material. Over a 24-hour period, the deer is not able to eat as much since that grass is still lying in the rumen from breakfast. Fewer pounds of food are taken in during the course of a day, plus there are less nutrients per pound — a double whammy for the animal. Professors told us in freshman biology that animals eat for their energy needs, but that is only true if the stomach will accommodate the load. Unlike cattle, deer have limited space in the rumen and cannot eat enough poor-quality forage to meet their needs. This is why deer avoid such things in their diets if possible. Among ruminants, deer have a relatively small rumen, presumably so they can be nimble and quick when chased by predators. Given this constraint, they need the very highest quality forage possible to make the best possible use of it. Otherwise the system slows down, and nutrient flow to the animal declines. Cattle, in contrast, have a large rumen in comparison to their body size and are able to make better use of coarse fiber. However, they can’t run 30 mph through a clearcut. Deer will suffer worse than cattle in a situation where forage becomes tougher and lower in quality.
When you see deer voluntarily eating coarse fiber, such as browsing twigs up to 1/4-inch in diameter, then you can be assured they are hungry, and their numbers probably exceed the carrying capacity of the land at that point in time, usually winter.
Deer in northern climates have a variety of survival strategies. In many situations, they will eat whatever browse they can find to keep the rumen functioning. But much of their energy needs come from accumulated body fat. Even in captivity, food intake by deer tends to be lower during winter months due to reduced activity levels. Starch in the diet during fall helps them put fat on their backs in preparation for winter.
Starchy feeds such as corn and acorns are also fermented in the rumen, but this is done by a different category of bacteria. Intake of starchy grains requires adaptation over time, and deer pick up the necessary bacteria from the environment as they feed. Ideally, the rumen bacterial populations are balanced and proportional to the current diet.
You may have read that supplementally feeding pellets or corn can be dangerous to deer during winter. Two factors set up such disasters. First, if deer are already starving when this food is introduced, they are more likely to gorge themselves on the grain. Second, the rumen bacterial population is not adapted to this new food source, and adaptation takes a period of weeks. Deer wind up with a very incompatible rumen that is full of grain. The grain ferments out of control, which produces an excess of lactic acid and causes rumen acidosis. If the rumen contents become very acidic, the rumen is damaged, and death can follow. Most state agencies and universities do not recommend feeding grain or hay to deer during winter months. If you are going to feed deer anyway, begin slowly on a limited basis when other forages are plentiful, and don’t quit until the spring green-up. This gives the deer a chance to gradually become accustomed to changes in diet.
Nutrition and behavior in wild deer are closely related, but getting a handle on what a deer will eat on a given day is almost impossible. All of us have observed deer taking bites of different plants with each step — even nibbling what looks to you like low-quality natural forages while they are standing on the edge of abundant clover in a quality food plot! Deer selectively feed each day as if choosing from a salad bar. Even captive deer will drive the nutritionist crazy with their sorting and selecting of feeds. The good news is that deer tend to go after the highest quality forages available. Unless there is some other barrier that affects intake, lush, young plants will attract them.
Plants also change from day to day. That alfalfa plant that was 28 percent protein and 30 percent fiber a couple weeks ago may be down to 17 percent protein and up to 45 percent fiber today. Next week it will drop even lower in quality. By the way, this is a major reason for cutting alfalfa, to rejuvenate nutritious top growth (See page 30 of this issue for more on alfalfa management). An advantage for browsers is that they can nip the tender tops of plants like alfalfa, thus avoiding the older, lower-quality plant parts, and still keep their nutritional intake fairly high. They also can switch to different plants as certain species mature. So, for some plants, deer help managers by changing feeding habits to maintain a high-quality diet. If deer are less picky about the plant parts they eat and are ransacking your plots, then there may be a food shortage on the property.
Overall, feeding deer is like feeding a fussy kid. One of my boys would take a pile of mixed vegetables, sort it by type, and eat each little piece in order of preference. All this by age two! If he was hungry, he would eat the carrots, but lima beans were always left behind. Deer are much the same way. Have you ever killed a deer in December, when the woods are dead-brown, yet were surprised to find the rumen contents were bright green? This is because the deer were sorting, nibbling and digging around for the best bites. Sometimes they are finding little green shoots under the leaves where they are not apparent to us.
Given this, how do you measure nutritional intake of the deer you are managing? Researchers have tried several methods, including leading tame deer around with a rope and watching what they eat or even monitoring feeding locations with a GPS receiver. Nearby plants are then sampled to mimic the way the deer were eating. Other experiments have focused on screening manure samples for microscopic bits of plants to get a handle on what deer eat. The methods at your disposal include screening and sorting rumen contents at the skinning pole, but few of us will tackle this job. Even fewer can identify all of the plants deer eat given a whole leaf, much less the tiny bits and pieces found in rumens.
Plant sampling is another option available to you. Much like soil testing, you clip samples of a crop or plant and submit them to a private lab or university Extension lab. Results are returned that reveal the levels of protein, digestible energy, mineral content and other characteristics. This information must be viewed for what it is — a snapshot in time of a single plant. If you collected the sample according to the lab’s guidelines, you can use this information to measure your success at producing nutritious, healthy, digestible crops or forages. This information can guide your future soil amendments and crop selection. But this does not measure the nutritional intake of your deer. As we have established, the plants change constantly, and so do deer feeding habits. Even if you could confine deer on your food plot with a fence, as cattle are confined, it would still be difficult for plant sampling to paint an accurate picture of nutritional intake.
You should apply common sense anytime you read or hear about forage analysis numbers. Orchardgrass can test 25 percent protein or 7 percent protein, depending on how and when it is sampled. Forage analysis numbers are valuable, but remember that they are not accurate indications of nutritional intake. Deer browsing on these plants in addition to other food sources may actually be getting more or less nutrition. Plants may be more or less valuable overall than a snapshot analysis suggests.
The Take-Home Lesson: Diversity
The lesson in all of this is not to measure your QDM program’s success based on the digestibility, protein level or other characteristic of an individual crop or plant. Instead, focus on providing nutrition in ways that suit the whitetail’s feeding behaviors and its changing nutritional needs through the seasons — in a word, diversify.
Providing diverse habitat allows the deer to selectively feed on the best plants each day. More diversity in food plots as well as naturally occurring plants in the local habitat will help spread the best quality over the longest period of time. Different plants reach their peak in digestibility at different dates, and protein and mineral levels tend to come along on the same schedule.
In general, based on the well-known, seasonal physiological needs of deer, focus on relatively higher protein forages in spring and summer, and worry more about energy during fall and winter months. We see good fall and early spring production from small grains such as wheat and rye. Clovers are at their best in spring and fall months. Brassicas offer very good nutrition over winter months. Summer annuals such as beans or peas are at their best during warm weather. Meanwhile, corn and sorghum can provide high energy grains to deer in fall and winter.
Diverse plots and habitat also reduce the risks of severe weather conditions. The deer at my place seem to prefer clover over birdsfoot trefoil, but in dry summer months the trefoil may be the only show in town. Another example is orchardgrass, which offers excellent early spring forage as it is one of the first plants to green up, but it quickly becomes overmature and, unless mowed, offers little to deer after early May.
Plants that handle dry weather and tough conditions are a valuable part of the manager’s toolbox. Consider including chicory, trefoil, or small burnet in clover plot mixes. Plant some sorghum in place of, or in addition to, corn.
Another way to improve forage quality for deer is to mow your perennial plots. Legumes and grasses put up nice tender growth from the roots, then the plant matures and develops seeds. After the plant flowers, new growth stops. If you clip these plots off at a height of 4 to 6 inches with a mower, the plants will produce another round of high-quality forage instead of going to seed. Intervals of a couple weeks to a couple months can be helpful depending on the situation. You can further spread out maturity by mowing plots in sections on a rotation rather than mowing entire plots at once. This is tough if you live far away, but it gets results. Clipping off the taller grasses and weeds will also allow sunlight to reach the valuable, low-growing clovers.
Again, food plots are only half the picture — practices like prescribed burning, timber thinning, browse cuts, winter disking or soil disturbance and other methods release and encourage natural forages. Planting of oak and soft-mast species where they are lacking helps fill the need for energy in the fall.
Whitetail nutrtion will continue to interest hunters, scientists and landowners. For QDM practitioners, deer behavior and nutrition are interrelated and must be considered together.
Deer nutrition can be improved by providing a balanced habitat with a variety of quality foods available in concert with the seasonal demands of these fine animals.
Mineral Needs and Nutrition:
Mineral needs of ruminants should also be considered a part of forage quality. We know that calcium, phosphorus and other minerals are required by deer. Deer maintain body stores of calcium and phosphorus primarily in bone. Bucks pull minerals from their skeletal structure when antler development begins, just as does do to produce milk for growing fawns. The take-home message is that mineral nutrition is long term; body stores are built over time. We can’t feed extra calcium in July and expect bigger racks in August.
Legume forages, such as clover and alfalfa, contain very high amounts of calcium. Corn, cereal grains and grasses are fairly low in calcium. However, all forages will be higher in mineral content when immature. As plants mature, mineral content declines along with protein content and overall digestibility. So we see the same relationship with mineral nutrition and deer density: if there is abundant feed available the deer will be able to select the most tender plants on a given day and likely get the best mineral content and adequate protein levels.
About the Author: Phil Anderson of Emlenton, Pennsylvania, has been a ruminant nutrition and management consultant for 13 years. After earning an Animal Science degree from Penn State, he served as a regional Extension educator for several years before starting his own business. He is a QDMA member who has enthusiastically hunted deer for 27 years. Phil is a member of the American Registry of Professional Animal Scientists and is currently working on a project to evaluate nutrition in populations of wild deer.