How Important is Mineral Supplementation for Deer?
More is Not Always Better
by: Larry Varner, Ph.D.
What causes a buck to drop his antlers in late winter and then start growing another set fairly soon? Basically, it’s all about day length. At the end of winter after the rut, a buck’s testosterone level drops dramatically and this initiates the process
of antler shedding. In the spring when days get longer the pituitary gland in his brain is stimulated to produce hormones that control bone growth. The first bone growth area to be stimulated is the pedicle.
Antlers can grow half an inch/day or more and are one of the fastest growing tissues in the animal kingdom. We know that antler size is affected by age, genetics and nutrition. Although other factors like stress, especially in breeder deer can have a big impact. Of these factors, nutrition is one of the easiest for a manager to control. If required nutrients are in short supply during the antler growth period, several things, all bad, can happen: (1) Antler growth rate slows down. Since antler growth occurs only for a limited time (about 120 days), an antler growing at the rate of 25 grams/ day is going to be larger at the end of that period than one growing at 15 grams/day; (2) Less dense antlers, which are more subject to breakage in rut fights; and (3) Desirable characteristics, which affect Boone & Crockett Score, such as antler mass (volume and weight), number of points and beam circumference are negatively affected by poor nutrition.
Priority of nutrient use in bucks is of particular importance. After needs for basal metabolism, growth, activity, and reproduction are met, what is left supports antler growth. Therefore, it is important that they consume a highly nutritious diet during antler growth since a period of inadequate nutrition may adversely influence antler development for several succeeding years. It is probable that a buck preferentially uses body nutrient stores during antler growth vs. nutrients from his diet. This may be why it’s so critical to have a buck in excellent body condition prior to the start of antler growth.
If a big buck grows 180 inches of antlers between March and the end of August, that’s about like you cutting off your arms and growing them back in four months. In the last third of antler growth about two-thirds of the mineral is deposited. During that time a buck cannot eat enough in a day to get all the minerals he needs to mineralize his antlers. He “borrows” it from within his body. In a process similar to osteoporosis in humans, minerals are taken from ribs, sternum and skull and deposited in the antlers. Bone density may decrease as much as 30 percent. That is why mineral nutrition even after antlers are finished growing is important. He has to replenish the minerals in his bones so he has enough for next year when he does the same thing again. Hardened antlers are high in minerals, mostly calcium (about 20%) and phosphorus\ (about 10%) in addition to a lot of trace minerals such as zinc, copper and manganese. This illustrates the importance of having adequate minerals in the diet when antlers are growing.
Regardless of what you might have been told, after a certain point putting more minerals in the feed doesn’t help. A buck can absorb only so much mineral each day no matter how much is in the feed. That raises the question “Should you feed a free choice mineral and if so, under what conditions?” My answer is yes because remember a deer’s digestive tract is relatively short so food passes through quickly. So even if you are feeding a high quality feed like AntlerMax® deer feed it is beneficial to have a consistent supply of supplemental minerals being consumed several times during the day. Minerals are utilized much more efficiently when they are “metered” gradually into the digestive tract throughout the day vs. a large amount at one time. It is even more important to feed a free choice mineral if you only have food plots or if you are feeding corn. If it is not in the soil, it won’t be in the food plot and corn is extremely low in many critical minerals required for antler growth.
When a new antler growth cycle starts remember a nutrient dense, balanced, highly palatable diet, fed free choice is critical since a diet that is low or marginal in one nutrient, may limit antler growth even though other nutrients may be adequate. Remember, especially with minerals, more is not always better. The key is having enough in the right ratio with other minerals in the feed. Anything more just goes out on the ground.
About the Author
Larry Varner was a research scientist in wildlife nutrition at the Texas A&M Experiment Station in Uvalde for 15 years. He has been a national and international consultant on wildlife nutrition and habitat management programs. He has been the deer nutritionist for Land O’ Lakes Purina Feed for over 20 years where he oversees the formulation, development and testing of deer feed and other wildlife products. You can reach Dr. Varner at [email protected].