You might recall the signs about not feeding bread to ducks. It’s also (among other carbohydrates) bad for deer.
There are several reasons for bread to be bad for ducks:
- dependency on humans as a source of food is just generally bad for wildlife,
- crowding caused by an attraction to food humans provide can increase the spread of disease,
- molding bread can make ducks sick
- bread is actually really poor in the nutrition ducks need
For deer, the reasoning is somewhat different. The first two risks, human dependency and spread of disease by crowding remain, but the rest is more complicated. Deer are ruminants, like cows, and rely on symbiotic bacteria to digest the sort of things we can’t. This means that, like us, deer and other ruminants have a gut microbiome that’s very important.
The gut microbiome has been studied to some degree since microscopy was developed (by Antonie van Leeuwenhoek, during the late 17th century), but much of the research on it is fairly recent. In general, it’s complex, important, somewhat diet dependent, disturbed by generalized antibiotics, influenced by probiotics, and likely associated with some diseases.
In humans we have enough research to conclude that disturbing the gut microbiome is probably a bad idea. In ruminants, this is extremely evident.
Diet changes the microbiome. In ruminants, the risk is that a system unaccustomed to carbohydrates is not a system that is ready to receive a lot of carbohydrates. Sudden influx of carbohydrates results in a massive increase in the digestive bacteria that thrive on those carbohydrates.
Like many organisms these have a competitive strategy that involves poisoning the competition (this is how yeast benefit from producing alcohol). In this case, the product produced is lactic acid. The net result? What in cattle is called “grain overload”. In more technical terms, rumen acidosis. Inflammation. Ulcers. Inability to absorb nutrients. The animal dies.
Corn. Grain. Birdseed. Hay. Apples. Anything notably higher in carbohydrates than what is available in the environment represents a hazard.
In Montana, feeding the deer is decidedly illegal (though I’m unclear if leaving your retired Christmas tree out for them qualifies- they will eat pine needles if given the opportunity, though it isn’t a preferred food source). And locally, the potential for disease to spread seems to be a primary concern: deer feeding has been cited as a factor in the high transmission rate of chronic wasting disease in Libby.