DIGESTION – A PIECE OF THE DEER NUTRITION PUZZLE Analysis of the ruminant digestive system – Part 1 By Matt Harper
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t is often said that the way to a man’s heart is through his stomach. Since I fall under that particular gender category, I can say with some expertise that this is a fairly accurate statement. After all, the male variety of Homo sapiens is a pretty simple beast. Supply a few basic needs and we are content. Whitetail deer are not that much different. If you are offended by my comparison, I apologize but you have to admit it’s a very close analogy. Give them food, cover and water and they will more than likely hang out close to where these basic needs are met. To narrow it down, let’s take water and cover out of the equation and just focus on food. Unquestionably, if you supply large amounts of highly attractive, highly nutritious food sources, deer will stay close to these food sources. I think it is fairly well accepted that planting food plots is an extremely effective way to supply these food sources. Much has been written about
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WHITETAIL NEWS / Vol. 16, No. 3
various aspects of food plots with articles ranging from how to plant to what to plant. This is all good information but little has been said about the subject of the system that utilizes these food sources; the deer’s digestive system. I am a firm believer in the value of seeing the entire picture of any endeavor I am involved with. Knowing how a deer’s digestive system works and how it can influence a whole host of things from food plot preference to deer activity can assist you in finishing the deer nutrition puzzle. So, in this article, we are going to begin a three-part series on the deer’s digestive system. In this issue, we will examine each part of the digestive system and how it works. Creation is an amazing thing. If you study the intricate detail in which living creatures are designed to have hundreds of parts working together in one complete synchronized mechanism, you will truly be astounded. The digestive system of a deer is one such example of a complex system of many parts working together to convert food into usable nutrients. It begins at the mouth. Deer are concentrate selectors or browsers, which means they pick and choose specific types of plants or even specific parts of a plant. The shape of a deer’s mouth coincides well with this particular feeding behavior. Deer have a long pointed muzzle with a fairly long tongue. This shape enables the deer to more easily pick and choose food stuffs. Compare this to the muzzle of a nonselective grazer such as a cow, which has a wide muzzle and acts more like a living lawn mower. Inside the mouth you will find incisors located only on the bottom. On the top is
a hard pallet which is used by the deer to nip off plants and plant parts as the bottom incisors lock the food stuff between them and the hard upper pallet. In the back are molars where the food is masticated by a figure-eight grinding and chewing motion, a similar chewing pattern used by most herbivores. This mastication of food stuffs is the very first step in the digestion process. Mastication is needed for efficient digestion to occur as the food stuffs consumed must be broken down into smaller particle sizes, thus increasing the total surface area of the food stuff. More surface area results in better enzyme activity and microorganism digestion as the food stuffs move further down the digestive system. All of this process is aided by saliva which has several functions. First, saliva is needed to aid in mastication. Also, saliva contains some enzymes such as lipase and pregastric esterase which is involved in the hydrolyses of short chain fatty acids. Yet another function of saliva is to act as a buffering agent. Finally, saliva contains mucin, urea, P, Mg and Cl all of which are needed by rumen microbes. After the food stuffs are chewed and swallowed, they move down the esophagus. The esophagus is the portion of the anatomy that is between the pharynx and the rumenreticulum. The main function of the esophagus is food transport. However, this does not only mean food transports down the digestion system but also back up as food boluses are regurgitated from the rumen-reticulum and brought back to the mouth for further mastication. This process is called rumination. The esophagus has the ability to expand and contract to move the food bolus either up or down during the rumination process. From here we move to the powerhouse section of the digestion system; the four-chambered stomach of the deer. Many people think that a deer has four stomachs. A more accurate description is that deer have one stomach with four chambers. The first of these chambers is a called the reticulum. The reticulum is often called the “honeycomb” due to its many irregular mucosal layers found there. These layers function as a filtering agent, trapping larger particles so that they can be further broken down before passing on through the digestive system.
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