As cold as it may sound....NONE! But it's to each their own really.
First scenario....
If you watch a lot of nature programmes as I do, mainly with Sir David Attenborough at the helm, you will soon learn that there is a policy that no animal in trouble, no matter how much it's plight may tug at the heartstrings, should be rescued by any of the team. Let nature take its course is the overwhelming policy. And I get that completely.
Second scenario....
Sir David Attenborough no where to be seen and you stumble upon a hapless, struggling animal. Do you help? You'd be sorely tempted, I know I would be. But the example in that report gives you two valid reasons why you should tread carefully....Disease, in this case rabies! Yikes! And also you just never know how the animal is going to react. They don't realise they're being helped, they just look on you as a potential threat on top of the problem they may already have.
I suppose it would depend on the animal too. If I came across a wild fox for example in trouble I'd think twice. If I came across a kitten in dire trouble I'd be there like a flash.
Totally legitimate viewpoint ^ but I am a softie in many ways and I just don't follow that rule. If I come across a wild animal, of any description, that is obviously on its way out and looks as though it might be in for a prolonged period of suffering, I will put it down as quickly and humanely as possible.
In other circumstances, I have twice stopped my car in farm country and risked some physical injury to free deer that were trapped in a barbed-wire fence. Both animals were quite exhausted but seemed otherwise unhurt, and I like to think that they recovered after wobbling into the bush; no way to know for sure.
I've also had an experience a few years back where a small buck was spotted hobbling painfully across my front yard, close to the road. One leg was dangling loose and useless; I later found that the bone was completely broken. Despite the pain this must have caused him, the annual rut was in full swing and the poor guy was still pushing himself to find and breed does. He had no chance to survive, and I burned my single deer tag to take him out of commission quickly rather than allowing him to continue on for probably several torturous more days. While this was during hunting season and I was licenced to take him, I bent several game laws by shooting him too close to the road and towards the road (making certain that there was no traffic within sight). The wound on his leg was obviously several days old already, and thoroughly infected and smelly, so we were not even able to utilize the meat. He wound up in the corner of the pasture to feed eagles, vultures and coyotes.
That might have been a completely natural injury...or maybe he was hit by a car, no way to tell. The turtles were being run over by traffic, and in today's world it's likely safe to say that most injured animals that are found by most people were probably hurt by the actions of people, directly or indirectly. So I don't feel I am interfering with nature; either way, the animal will be recycled by other critters, I just edit out that part where it suffers for days, or is eaten alive...yes, that happens often...but the calories and nourishment in the carcass never goes to waste.
How about animals that have come to grief in an entirely natural manner, with no connection to human action? Sir Attenborough has been a hero of mine for much of my life and I know that he espouses the "no interference" rule, as do many naturalists, but I don't subscribe to that. The end result is the death of the animal; I simply won't tolerate unnecessary suffering, when there will be no difference to the natural system if reducing the pain is possible.
Yeah, I know, I know..."You say one thing...but you're a hunter and kill animals yourself!" Yes, I do, and there is no contradiction or paradox involved here; I love animals and nature, and while hunting my primary concern is that death is as quick and humane as possible. I'll guarantee that the vast majority of animals taken by ethical hunters suffer far less than they would while falling victim to almost any "natural" end.