range may not exhibit the stark, overused appearance one would expect, the land’s nutritional base and capacity to naturally sustain healthy deer steadily declines with continued overuse.
walk along slowly, eating “some of this” combined with “a little of that,” thereby selecting the proper mix of nutrients to meet their immediate dietary needs. RESPONSE TO CHANGE
AUTUMN The whitetail’s feeding habits are extremely variable and opportunistic, in addition to being highly selective. Their diverse feeding habits change with the seasons, allowing them to choose a wide variety of foods, including grasses, sedges, fruits, nuts, forbs and mushrooms, in addition to portions of those shrubs and trees that best meet their nutritional requirements. Since their diet changes so dramatically with the seasons, it’s also important to note that their digestive tract can change with diet, but gradually so. The amount of saliva produced, the lining of the rumen and the rumen’s size, for example, change seasonally to compensate for the shift from eating succulent summer forage to a more-fibrous winter diet, and back again to more luscious foods with spring green-up. However, it takes two to three weeks for the rumen microbes to completely adjust to a new diet.
Commencing about mid-March, in response to increasing hours of daylight hours (photoperiod), deer change immensely in basic physiological processes and general behavior. Their metabolism rises and they become more active, pregnant does carry rapidly growing fetuses, young animals resume body growth and adult bucks start growing antlers. It’s a time when huge amounts of nutritious forage in the form of succulent new herbaceous growth high in protein, energy and essential minerals and vitamins are essential to herd welfare. Bucks also require minerals and vitamins for antler growth, but researchers still debate the exact amount. The whitetail’s spring diet is probably more diverse, in terms of quantity and quality, than it is during any other time of the year. It can change rather sharply within a few days, as governed by soil type, rate of snow melt, temperature, amount of moisture and other factors. On a northern range, the deer’s spring diet can change from being nutritionally poor to excellent within a few days. There are many complex nutritional relationships that make diet diversity important for whitetails. Even good deer foods vary in their specific nutrient value. Early forbs, legumes and grasses, for example, tend to be highly digestible and contain high levels of protein, phosphorus and potassium. On the other hand, leaves of woody species, although poorly digestible, provide significant amounts of fermentable cell solubles, and high calcium content. Also, eating certain plants tends to aid in the digestion of others. Researchers have learned although some plants may be high in protein or digestible energy, they are too low in nitrogen, phosphorus, magnesium or sulfur for adequate rumen function. But such nutrient-deficient plants may be utilized if they are eaten in combination with other plants high in the deficient elements. Hence, forages cannot be ranked low in quality simply because they do not meet all the whitetail’s nutritional demands. Whatever the reasons may be, poor nutrition during the spring period will impact the health and well-being of all deer. An inadequate spring diet will cause poor growth among young deer, retard buck antler growth and contribute to poor fetal development, ultimately leading to high newborn fawn mortality. SUMMER Good nutrition during summer is critical for favorable fawn growth. If the doe receives insufficient protein to support normal milk production, her milk will be of uniformly
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During the most brutal periods of winter, deer will resort to any forage that is available, even very fibrous forages.
high quality but the total amount produced will decline. Hence, a doe living on poor range might produce a limited milk supply and ultimately raise relatively small fawns because of it. If fawns are to achieve their maximum skeletal size and body weight prior to winter, they require nourishing forage that has from 14 to 22 percent protein content. When researchers compared performance on diets containing 8, 13 or 20 percent protein, female fawns were found to make maximum gains on 13 percent protein while male fawns performed maximally on 20 percent. The fawn also needs minerals in their diet for proper growth. By comparison, yearlings, which also are still growing, require 11 percent protein, whereas mature animals may require 6 to 10 percent protein in their diets for body maintenance. Some researchers suggest that if crude protein levels in deer forage fall below 6 to 7 percent, rumen function is seriously impaired. Individual plant species and plant parts change in their nutritive value with maturity. Certain forbs, grasses and even sedges may be succulent and highly digestible when they first appear, but become hardened and fibrous at maturity. Therefore, in a chosen feeding area, an expanding deer herd can systematically and drastically reduce, or even eliminate, certain preferred plants. At the same time, other plants may increase either because they’re less palatable, resistant to grazing, or both. Although severely overgrazed
John Ozoga
SPRING
With the shortening days of autumn, whitetails become more active — almost unbelievably so. Autumn is not only the whitetail’s breeding time, it is also that critical period when deer prepare for the forthcoming, stressful winter season when their nutritional needs change and when patterns of deer range use change. Energy-rich foods high in carbohydrates such as acorns, beechnuts other starchy mast crops, as well as apples, cherries, grapes and a host of wild-growing and cultivated crops are choice foods because they promote fattening. When available, a deer will eat about 1.5 pounds of acorns daily per 100 pounds of body weight. Because fat reserves can be metabolized more readily than protein for energy needs when nutritious forage is scarce, storing fat in autumn is a mechanism that enhances deer survival during the winter months. Like other seasonal events in the whitetail’s life, the accumulation of fat is cued to photoperiod and is hormonally controlled. It is an obligatory process, meaning that all deer are inclined to become fat in autumn. Adult bucks usually commence fattening earlier than other deer. They are also the first to molt into their winter coat, usually in early September, about the time they shed antler velvet. Prime-age bucks will be “hog fat” by early October, but may lose 20 percent or more of their body weight during their four or five weeks of strenuous rutting activity and enter winter relatively lean. Because fawns must simultaneously grow and fatten, they seldom achieve their maximum size and fatness until December. Given favorable nutrition, however, they may double their body weight between weaning and the start of winter. As a result, fawns are particularly sensitive to the adverse effects of deer overpopulation, drought or early snow cover that may bring about food shortages for them in autumn. The importance of digestible energy versus protein content in the autumn diet of fawns was demonstrated in our studies at Cusino. During a 10-week period, fawns provided diets high in energy (3,000 kcal per kilogram of pelletized feed) exhibited better body growth and fatness, as compared to those fed low (2,700 kcal) energy diets, regardless of feed protein content (16.2 percent or 6.6 percent). As a result, we concluded that level of protein in the autumn diet of fawns had minimal impact upon their wellbeing, whereas even minor reductions in the amount of digestible energy slowed their growth rate and decreased their level of fatness. Surprisingly, however, even fawns on restricted autumn rations accumulate some fat at the expense of additional skeletal growth. In other words, healthy fawns tend to be skeletally large and fat, whereas malnourished fawns may be fairly fat, but stunted. Autumn nutrition also affects older female whitetails. The pattern of coat molt, rate of fattening and the conception rate (and date) among adult does may be quite variable but will hinge heavily upon their nutritional status prior to the rut. Yearling does are especially sensitive to nutritional stress because they must put on appreciable body growth during the summer months — as much as a third of the yearlings might fail to breed if subjected to nutritional shortage prior to the rut. We often see nursing does in red summer coats longer than does that fail to raise fawns. One reason for this difference is chemistry, claims Canadian researcher George Bubenik. Prolactin, “the hormone from the pituitary gland that, when declining and acting with other hormones, signals the Vol. 16, No. 1 /
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