The Importance of Fiber in Deer Diets

Shane Horrocks M.S.
Wildlife Nutritionist
MaxRax Wildlife Nutrition, Inc.

Whitetail Deer are adapted to utilize fibrous plant material as a daily source of energy or carbohydrates. Fibrous material is composed of cellulose, hemicellulose, pectin, and lignin, where hemicellulose and cellulose are the primary sources of energy. Fiber is broken down in the rumen by enzymes produced by microorganisms, then converted to energy, proteins, and vitamins.  But why feed fiber if you are already providing the deer with protein, energy, and vitamins?

The importance of feeding adequate fiber in deer diets (total daily consumption) is to maintain optimal rumen function. In order to maximize deer production, the correct concentrations and ratios of protein, energy and fiber must be present in the diet.

Fiber must be of good quality and quantity to facilitate rumen health.  Crude fiber, or total fiber, is important to consider, but accurate amounts of Neutral Detergent Fiber (NDF) and Acid Detergent Fiber (ADF), two different qualities of fiber, must also be considered and balanced to achieve proper rumen health and accurate use of the total fiber. Neutral Detergent Fiber is more digestible fiber, while Acid Detergent Fiber will promote cud chewing. When a deer chews their cud, they are mechanically breaking down the fiber which allows greater fermentation of the fiber in the rumen.  As fermentation occurs, acids are constantly produced and secreted into the rumen, which lowers rumen pH. However, saliva contains an antacid known as sodium bicarbonate, that balances the acidity of the rumen. Saliva production increases as a result of more cud chewing, which occurs when accurate amounts of good quality fiber are present in the diet.

Particle size is also critical to fiber digestion and utilization.  If fiber particle size is small, it is more easily passed through the rumen and into the intestine. Good fiber should remain in the rumen long enough to be fermented, which is why supplemental hay and grass (or natural browse) can be beneficial. Particle size also impacts rumen muscle stimulation. The rumen tissue is partially comprised of muscle that is constantly contracting and relaxing, allowing for proper mixing of feed and hay. When fiber particles rub or scratch the inside of the rumen wall, they stimulate muscle contraction. Without muscle contraction, feed digestion in the rumen is reduced and can lead to inefficient bacterial growth.

Additional benefits from fiber are the production of volatile fatty acids like acetate and butyrate. Acetate and butyrate are produced from the fermentation of fiber and are used as an energy sources. During lactation, does can utilize acetate to produce more milkfat, and acetate is also responsible for the development and growth of the rumen in fawns, which occurs approximately two weeks after birth.  Butyrate helps to facilitate the growth of rumen villi responsible for absorbing energy and nitrogen. Butyrate can also cause the villi in the small intestine to grow in length, which increases the intestinal surface area available for absorption of nutrients (amino acids, fat, carbohydrates) from the feed.

Finally, fiber present in the small intestine can also help to irreversibly bind toxins circulating in the bloodstream so they are safely excreted in the feces.

A good quality plane of nutrition for deer always has good fiber quantity and quality. Deer should always consume appropriate amounts of good quality fiber on a daily basis. If fiber is not present in the feed, be sure to supplement fiber in the form of hay or high quality browse/grass. The amount of fiber needed in the feed on a daily basis will depend on several factors such as animal age, sex, stage of production, current diet, available browse, and amount of hay supplemented daily. Consult a wildlife nutritionist to determine appropriate fiber concentrations in your feed.