For all toxins, including those in plants, the dose makes the poison. Many plants that are lethal when eaten in large quantities can be non-lethal and even medicinal when eaten in small quantities. Most wild animals know this, and will intuitively limit their consumption of plants that could be lethal in large quantities. Domestic animals, for reasons I don't understand, have often lost this ability. Cows and sheep are the best examples, while goats seem to have more of their original instincts remaining.
This, in my opinion, is a really important reason to eat wild meat because in addition to the protein and high omega-3 fats you also get all of the plant medicines that the animal ate. In raised animals, even cows that are 100% grass fed, their diet is not very diverse and they get to eat very few herbs that might have medicinal value. So the meat won't have the same nutritional and medicinal value as that from a wild animal.
This also works for people. I, for instance, eat poison ivy throughout the year in small quantities. Its primary medicinal benefit is that eating it in small amounts makes me immune to the oil, which usually causes severe contact dermatitis in most people. Before I started incorporating it into my spring and summer diet, I would have horrible reactions to the plant and had to go to the doctor on a few occasions for steroid prescriptions to get the rashes under control. Now, even after severe exposures, I rarely get more than a tiny, tiny reaction consisting of perhaps one or two pinhead-sized blisters, which heal in a day or two.
It's not just instinct. The animals LEARN what to eat. If you confine cows to a pasture of nothing but grass and clover, they will never learn to eat weeds. You can teach cows to eat things that they normally wouldn't eat, like thistle. Start with cows trained to eat out of a pail, pick thistle and feed in the pails coated with molasses. Slowly take away the molasses and just feed thistle. Suddenly you have cows that like to eat thistle. Animals learn from their mothers what is good to eat. There are cows out there that have never tasted grain and will refuse it if offered to them.
I have watched my cows eat raspberry leaves, ash trees, cherry trees, ferns, sorrel...
Another factor however is that cows are designed to eat grass. That's their staple. Goats are designed to eat woody shrubs and sheep are designed to eat broad leaved herbs. There are reasons why sheep have it worse than cows and cows have it worse than goats when figuring out poisonous plants. I am really not sure what those reasons are. Something about goats isn't totally domesticated. It's known among goat people that you must never lose a fight with your herd sire, because if you do there is the possibility that your hole heard can turn back into the wild.
I don't think there is any wild game that puts on fat like a beef cow or sheep does and in my book that makes both of them nutritiously superior in that department. Also, in the U.S. deer get fed lots of corn and soy by hunters and wild boar and bear and most vermin eat all kinds of garbage and maraud conventional farms. If you are lucky enough to live in pristine wilderness, then more power to you.
Also, in U.S. deer are overpopulated and often not very healthy, I have helped slaughter a deer that was absolutely COVERED in keds, have heard of deer covered in ticks. My goats never have more than a few ticks or a few keds.
Masanobu Fukuoka said something along the lines of "to my horror I discovered that nature was no longer truly natural, and humanity no longer truly human".
Dorothy, I wouldn't worry so much about feeding your dogs slankers, I highly doubt it's going to hurt them. I don't think it would hurt us most likely either, however I just don't agree with their practices, I would want to support farmers who use practices I believe in. Some people, especially youngsters or those with chemical sensitivities, may be harmed by slankers. It is probably almost totally impossible to quantify what harm could be done to them.