When shooting at a deer from 10 or 15 yards, an experienced shooter with a 35-pound bow is highly likely to kill it. It all depends on the size of the deer and how much force you can apply to its body. With modern bows, we usually don't kill animals with one shot, so you need to understand that when you use a heavy bow, you're actually trying to injure or at least make unconscious your target so that it doesn't run away.
In general, if you know what kind of animal you're shooting at and can estimate its weight, you can figure out how hard you should shoot to kill it. For example, if you think the deer is too big to be killed by a single arrow, then you should shoot harder than if it were another time. Or let's say you're hunting in a region where those things happen regularly - like in certain parts of Canada or America - then you should learn how hard it is there first before you start shooting too hard otherwise you might cause unnecessary suffering. Of course, if you hit something other than the deer, you'll need to check it out but only after making sure that it isn't the deer you were aiming at in the first place!
That's not to say that shooting proper poundage isn't vital while bowhunting; it is, but mostly because it plays a big role in the amount of kinetic energy a bow and arrow configuration can generate. It all depends on what kind of deer you're hunting and where you place your shots. A deer's weight has very little to do with determining if you'll be able to kill it with a bow.
When hunting large game with a high-powered rifle, many shooters prefer to use bullets that are between.375 and.500 caliber because they provide reliable expansion within the body of the animal and still offer enough velocity to produce significant terminal effects. With rifles, more is usually better. The heavier the bullet, the more damage that can be done with each shot.
With a bow, however, you need to consider how much force you can generate with your arm muscles before you start causing injury to yourself. Generally speaking, the stronger you are, the more power you can generate with your arms, which means you can shoot larger arrows and hit harder targets. However, there are limits to how strong anyone can get their arms before tearing them apart. In fact, the strongest person I know uses 70 pounds as his maximum draw weight for his bow. He can only draw it for a few seconds before it becomes too hard for him to hold.
Even with a 70-pound bow, a shot to a deer's lower leg will not be deadly. A broadhead inserted into the animal's heart or lungs guarantees rapid, merciful euthanasia. Shoot distance: the closer your shoot, the quicker and more powerful your arrow. Close shots are also simpler to execute since your target looks to be larger. You can't miss at close range.
However, a deer's vital organs are protected by bone and muscle, which reduces the risk of serious injury from an arrow. Still, it is best to avoid these areas when hunting so as not to cause unnecessary pain to the deer.
An average-size deer can produce up to 20 feet pounds of venison. So, yes, a 70-pound bow can kill a deer. But it depends on how the deer dies and where the arrow goes. An arrow that doesn't reach its target area may not be enough to do any real damage. And an arrow that misses its mark but hits something else may still cause harm. For example, an arrow that enters the side of a deer could go through its liver, causing internal bleeding and death. This would not be intended, but it could happen.
Also, keep in mind that even if you don't kill the deer, it can still suffer injury from your presence and the stress of being caught in the crossfire of a gunfight. It's best to let nature take its course when hunting with a heavy bow.
A 40-pound bow would easily kill a deer if the shot placement is correct, and it's probably the bare minimum I'd use. After years of shooting a 70# compound, I was able to easily shoot a 58# longbow when I was younger. I've had to lose weight as I've become older, and I now shoot a 51# recurve. The key here is practice; you need to be able to accurately shoot a heavy bow. If you can't do this yet, then start with a lighter one and work your way up.
Here are some tips for successful hunting with a heavy bow:
First, choose your spot carefully. Deer tend to avoid areas where other deer are likely to be found, so look for places where there's little human activity. This might mean less cover for animals, but it will make your job easier. Keep an eye out for signs that deer have been eating during the week ahead of time; this will give you an idea of what kinds of food are available and how much effort they'll be willing to put into finding it.
Second, know your equipment. Make sure you have enough arrows on hand to account for missed shots; you don't want to run out before you get your chance at an animal. Also, consider using rope or chains as a handle for heavier bows; this will help you keep your balance and not fatigue yourself too quickly.