This is a pretty good article explaining the feeding of deer.
Feeding Deer Harms their Health
CONCORD, N.H. -- Good Samaritans who think they're helping deer by putting out feed in the winter may actually be endangering the health of the herd, says New Hampshire Fish and Game Department wildlife biologist Kent Gustafson.
"People mean well, but don't realize the damage they're doing. Feeding wild white-tailed deer may actually reduce the animals' ability to survive a New England winter, making them more vulnerable to starvation, predation, disease and vehicle collisions," says Gustafson, who is the Deer Project Leader for Fish and Game. "Despite people's good intentions, supplemental feeding creates an artificial situation in which the deer, the habitat and the public may suffer."
The commercial availability of so-called "deer feed" does NOT make it OK to feed the deer, according to Gustafson. The Fish and Game Department urges landowners to NOT provide supplemental feed to deer, because the practice actually can cause far more harm than good.
"Many people think of feeding deer like feeding the birds," remarks Gustafson, "But there are some critical differences that make feeding deer unhealthy for the deer population, for plants near the feed site and for passing motorists."
Problems start because feed sites congregate deer into unnaturally high densities. These high deer densities can spread diseases among deer and attract predators, increasing the risk of death by coyotes or domestic dogs. It can cause aggression in the herd, wasting deer's vital energy reserves and leading to injury or death; as well as using up critical fat reserves as deer expend energy traveling to and from the feed site. Feeding can deny access to food for subordinate deer and fawns, and can encourage over-browsing of local vegetation and ornamental plants. It also increases the likelihood of deer-vehicle collisions.
One of the most serious drawbacks to feeding deer is that feed sites lure them away from their natural wintering areas. This attraction can trap deer in inferior winter habitat and increase the chance of malnutrition and predation. If deer continually go to feed sites instead of natural deer wintering areas, then young deer may never learn to find their traditional winter habitat. Also, landowners may not see the value of managing for dense softwood cover, typical natural winter habitat for deer.
Habitat is critical, because in winter conditions, deer conserve their energy, getting as much as 40 percent of their daily energy during winter from their fat tissue. That's why in winter, COVER -- not food -- is the key to deer survival. Deer retreat to softwood cover, or "deer yards," to avoid deep snow, high winds and extreme cold. In these areas, deer move around very little, using a network of trails that disperses them and reduces competition for natural food.
"Quality natural habitat provides the best insurance for deer survival in winter," says Gustafson. "If you care about deer, leave them alone -- let them be wild, and find natural foods and appropriate winter shelter on their own. The bottom line is, please don't feed the deer, and please discourage your neighbors, friends and relatives from engaging in this harmful activity."