Can Baiting and Feeding Really Spread Deer Diseases Faster?

August 9, 2023 By: Kip Adams

Baiting and supplemental feeding are contentious topics in hunting camps, wildlife agency headquarters and legislative halls across North America. They come with cultural, ethical and ecological considerations. These are all worthy of discussion, but I’ll leave the cultural and ethical topics for another time and focus on the ecological points. Specifically, let’s look at the scientific evidence for increased deer disease transmission at bait and feed sites.

By design, baiting and supplemental feeding concentrate deer and other wildlife species for the purposes of hunting, trapping, viewing, or simply increasing nutrition available to the animals. Some argue baiting and feeding have positive attributes, but no one can disagree they have numerous negative implications to a deer herd, including altering animal behavior, degrading the habitat near bait and feed sites, increasing the susceptibility to predation, and greatly enhancing the opportunity for disease transmission

Baiting Affects Deer Behavior

Whatever the intended purpose, bait and feed sites congregate deer in unnaturally high densities and keep them returning to small areas. This human-altered scenario is very different from a deer herd’s natural behavior. Depending on time of year, they typically exist in small family and bachelor groups distributed widely across the landscape. This evolved social behavior allows them to capitalize on food and cover sources while minimizing crowding, stress, habitat degradation, and disease transmission.

Abundant research by the University of Georgia, Texas A&M University-Kingsville, Connecticut Department of Environmental Protection and others highlights how easily deer are attracted to bait/feed sites for research and hunting purposes, and how these sites increase deer-to-deer contact rates. If one or more animals are harboring a pathogen or parasite, its spread to additional animals is enhanced by increased animal-to-animal contact at bait/feed sites. While deer may not leave their home range to visit these sites, they quickly shift their core area or establish a new core area closer to bait/feed sites. This behavior may provide an additional food source, but it comes with numerous negative, and sometimes deadly, aspects.

prescribed fire
The NDA supports providing adequate food and cover for deer through habitat management efforts, like prescribed fire. The NDA does not support supplemental feeding in known CWD and bovine TB areas or where this activity may disrupt natural migratory patterns of deer.

Bait/feed sites artificially elevate the number of deer visiting a specific spot of land. Those deer are home to a host of potential parasites and pathogens including lice, ticks, mites, bacteria, viruses and more. Many of these are shared directly with other deer at bait/feed sites while many are also left at the site and shared indirectly with deer visiting at a later time. Let’s review some examples of diseases exacerbated by bait/feed sites.

Deer Mange

Deer mange is a skin disease caused by parasitic mites and characterized by intense scratching and hair loss. According to Maine’s Department of Inland Fisheries and Wildlife, deer at feed sites in their state have suffered outbreaks of demodectic mange, and University of Alberta researchers have reported elk at the National Elk Refuge in Wyoming have suffered outbreaks of psoroptic mange at winter feeding sites. Each year 20 to 30 adult bulls die from psoroptic mange, and infected elk serve as a reservoir for infection of a nearby population of bighorn sheep. 

Mange is spread by mites transferring from an infected animal to another when they come in direct physical contact. Mite larvae and nymphs can also fall off an infected animal and survive in the environment for several weeks. When an uninfected animal encounters the contaminated environment, the mites can infect the new animal. Hence, animals congregated at bait/feed sites are at enhanced risk to contract and spread mange.

Natural foods like crabapples (shown here) and acorns do not equal the same disease threat as most bait and feed sites because peak attraction at any one tree lasts less than a month each year and is usually spread out across the landscape at numerous trees.

Bovine Tuberculosis

Bovine tuberculosis is a bacterial disease affecting deer, livestock and humans. Tuberculosis was detected in a free-ranging deer population in northeast Michigan in 1994 and has remained in the population since. Abundant research by the Michigan Department of Natural Resources, Department of Agriculture and Michigan State University show infected deer shed the bacteria through respiratory secretions, feces and urine, and the bacteria can remain viable in the environment for months. Tuberculosis spreads when an uninfected deer comes into direct contact with secretions from an infected animal or indirectly with the bacteria at a contaminated site, and it is exacerbated by crowding and stress. 

Disease experts agree that as long as widespread baiting and feeding continue in northeast Michigan, successful eradication of tuberculosis is likely unattainable. Since bait/feed sites concentrate deer and their urine, feces and respiratory secretions, they are the primary means for tuberculosis transmission. Hence, animals congregated at bait/feed sites are at enhanced risk to contract and spread tuberculosis.

Bovine Brucellosis

Bovine brucellosis is another bacterial disease affecting elk, bison, livestock and humans. Infected animals often experience a termination of pregnancy. Researchers with the U.S. Geological Survey and numerous universities show brucellosis is spread by direct contact with infected animals or a contaminated environment. Brucellosis bacteria are present in the aborted fetus, placenta, fetal fluids and vaginal discharges of infected females. The disease can be transmitted when other animals lick these infected materials, or when animals consume contaminated food or water. Infection can spread via inhalation and exposure of the eyes or open wounds to contaminated materials. The bacteria have been shown to remain infective in the environment for several months. 

This disease receives national attention for its presence in elk in the Greater Yellowstone Ecosystem. It is enhanced in this population as a direct result of a winter-feeding program that produces a high density of elk on the feed sites. Importantly, the disease is not found among free-ranging elk herds in the area surviving on natural forage and not congregated at the feed sites. Hence, animals congregated at bait/feed sites are at enhanced risk to contract and spread brucellosis.

The NDA opposes the expansion of baiting where it is not currently legal. The NDA will not work to repeal baiting where it is currently legal, except where CWD or another known disease is present.

Chronic Wasting Disease

Chronic wasting disease (CWD) affects deer, elk, moose and reindeer, and is caused by a prion which is a misfolded protein molecule. It is different than a bacteria or virus and is thus confusing for many hunters and the general public. CWD has a long incubation period of 18 to 24 months, and while animals can shed infectious materials and infect other animals during this period, they show no outward signs of the disease. Externally, they appear completely healthy to the human eye, but internally the disease is eating holes in their brain, so diseased deer die at 2 to 4.5 times the rate of healthy deer via vehicle accidents, predators, hunters and other causes. 

“Michigan State University researchers documented deer using heat emanating from their mouths and nostrils to thaw frozen bait/feed, thus sharing saliva and nasal droppings.”

CWD is spread directly between animals via saliva, blood, urine and feces and indirectly through environmental contamination of soil, food and water. Researchers have documented prion concentrations at bait sites in CWD-infected areas, and they’ve determined CWD is both contagious and self-sustaining in a deer herd. The potential for transmission from the environment depends on contamination levels and the resistance of prions to breakdown. 

Unfortunately, according to Cornell University’s Dr. Krysten Schuler, CWD prions have been shown to remain infectious in the environment for at least two years. According to Colorado Parks and Wildlife Department’s Dr. Mike Miller, this greatly increases the disease transmission potential at bait/feed sites where saliva, urine and feces are deposited at levels much greater than other areas throughout an animal’s home range. 

In addition, Michigan State University researchers documented an especially alarming behavior among deer using frozen bait/feed piles. Deer used heat emanating from their mouths and nostrils to thaw frozen bait/feed, and researchers reported observing numerous deer working the same bait/feed piles and thus sharing saliva and nasal droppings. Hence, animals congregated at bait/feed sites are at enhanced risk to contract and spread CWD.

Food Plots Don’t Equal Baiting

Some people equate food plots to baiting and argue they should be illegal where baiting is not allowed. That is flawed logic, which explains why not a single state outlaws food plots. The differences are many, but the main reasons food plots don’t transmit diseases the way bait/feed sites do is their size and amount of food produced. Food plots spread deer out over a much larger area and allow deer to forage above ground and away from saliva, urine and feces. For most food plot species, once a deer takes a bite, the forage is gone so another deer is not putting its mouth in the exact same spot. All these factors reduce deer-to-deer contact and animal contact with a contaminated environment.

Food plots spread deer out over large areas and allow them to forage above dirt level. For most forage species, once a deer takes a bite, the forage is gone so another deer is not putting its mouth in the exact same spot.

Multiple Threats at Bait and Feed Sites

University of Saskatchewan and Aarhus University (Denmark) researchers showed concentrations of wildlife are a breeding ground for amplified disease transmission. It is important to recognize the risk is directly enhanced at bait/feed sites due to the increased number of animals visiting a specific location. However, it is equally important to recognize the risk is also indirectly enhanced via the mites, bacteria and other infectious materials left behind by infected animals at these sites. Further, artificial congregation of animals has been documented to induce stress responses in individuals, leading to reduced immune function and increased disease susceptibility. 

A national survey of state wildlife agencies for our 2017 Whitetail Report showed baiting was allowed in some form in 26 states. Due to continued spread of CWD, that number has dropped to 22 states today, and it is likely to decline even further in the future. 

Regardless of your cultural and ethical views toward baiting/feeding wildlife, there is no doubt about the dangers these practices pose to animals through increased disease transmission. It is clear from scientific evidence that baiting and feeding significantly increase the spread of diseases among deer by congregating them unnaturally on small sites. Artificially high concentrations of deer, elk and other animals may be fun to view by some, but the congregations are neither natural nor advantageous for those animals or ones that will visit those sites in the future.

To read NDA’s official position on baiting, feeding and other matters, view our complete position statements online.

About Kip Adams:

Kip Adams of Knoxville, Pennsylvania, is a certified wildlife biologist and NDA's Chief Conservation Officer. He has a bachelor's degree in wildlife and fisheries science from Penn State University and a master's in wildlife from the University of New Hampshire. He's also a certified taxidermist. Before joining NDA, Kip was the deer and bear biologist for the New Hampshire Fish & Game Department. Kip and his wife Amy have a daughter, Katie, and a son, Bo.