Deer need to consume energy to maintain their bodies as is (maintenance energy) and even more energy to grow, reproduce, and produce antlers.  In addition to energy, the six required nutrients for deer are protein, fat, carbohydrates (fiber, sugar, starch), minerals, vitamins, and water.  The key is for deer to receive a balance of energy and nutrients to meet their requirement given their stage of production.

 How Is Deer Feed Energy Calculated?

 In animal nutrition, the amount of energy in deer feed is calculated as Total Digestible Nutrients (TDN) or as Calories (kilocalories).  This dietary energy be it browse, hay, corn, or pellets is derived from the feed’s nutrients (protein, fat, and carbohydrates).  Fat contains 2.25 times more energy than does protein and carbohydrates. As the animal increases in body size, pregnant with multiple fawns, producing milk for twins or triplets or growing an exceptional rack of antlers, the amount of dietary energy needed daily increases.  The animal will increase its intake to meet its energy needs to a point where the animal cannot consume enough feed¹ (Ammann et al., 1973).  This explains why a doe producing milk for four fawns may lose more body condition than the doe lactating for two.

Goal of Supplement Feeding Program

 Additionally, to make a feed that is higher in dietary energy, it requires an increase in protein, fat, or carbohydrates and decreases the room for the other nutrients (minerals and vitamins) that are required for deer to excel.  It can also lead to digestive upset.  A feed too high in fat can suppress fiber digestion and a feed too high in soluble carbohydrates (sugar and starch) may promote acidosis.
 
The key is balance.  The supplemental feed needs to have an energy content that is needed by the animal and at a rate of consumption that provides the nutrients (protein, minerals and vitamins) to complement the native forage and meet the needs of its stage of production and genetic potential.
 
¹Ammann, A.P., R.L. Cowan, C.L. Mothershead, B.R. Baumgardt. 1973.  Dry matter and energy intake in relation to digestibility in white-tailed deer. Journal of Wildlife Management 37:195-201.