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Snake bite in horses is often fatal because more often than not they will get bitten on the face and because of this area's very high blood supply they tend to absorb a lot of poison and therefore tend to not to do very well.
Secondly, usually by the time people notice something's wrong the damage is already done. As a consequence quite a large number of snake bitten horses that I have seen have died. I think that it is related to how long it takes for the reaction to occur before you realize that the horse is sick.
The other problem is getting enough anti-venom of the correct type into them. There are several types of specific antivenoms (black snake, brown snake, tiger snake etc), and there is polyvalent antivenom which is to multiple species and correspondingly expensive.
Generally speaking with anti-venoms, the time to get them in is before the horse displays major clinical signs. Once you have got major clinical signs, the damage has already been done. Then the anti-venom can stop any more damage, but the damage that has already been done may not be reversible. That kind of damage takes time to sort itself out and the question is whether the damage is so severe that it will get beyond the ability for the body to repair, and whether the horse's system can be supported until the repair occurs.
The signs of snakebite are usually weakness and collapse. The weakness tends to be progressive. That is, it starts in the back and then works forward. It gradually gets worse. They then tend to spend more time lying down. It then progresses further to paralysis of the diaphragm and chest muscles and subsequently death.
Snakebite can cause extensive muscle damage which means you can get quite a lot of myoglobin (which is the red part of the muscle) which leaks out and gets into the bloodstream, runs around it and jams up all the kidneys. Once the kidneys are clogged up with myoglobin, there isn't any easy way to unclog them and the horse can therefore die of kidney failure. Sometimes you get them past the collapsed stage and they still die of kidney failure.
You can also get damage to the various homeostatic systems of the body such as clotting mechanisms, so one symptom sometimes seen is bleeding, either from the nose or mouth, or into mucous membranes such as the gums.
The other thing that often happens – also in dogs particularly – is that they get a bad bite from a snake and collapse within ½ an hour but then they will get up again in a while and they wander around fine for a couple of hours and then they collapse again. It's the second-time-collapse that they tend to die in. We are not really sure what happens at times but, for example, I remember many, many years ago, getting called by a client who lived 5 minutes from the surgery and he said: "I have just seen my horse getting bitten by a big brown snake!" I jumped in the car and raced straight up there and literally it wouldn't have been more than 10 minutes before I got there and the horse was dead. It was bitten on the face. There was a big possibility that it was a King Brown snake, but that is an example of how fast it can happen.
Regardless of how big the horse is, it is a question of how much venom is injected. If you see your horse has been bitten by a snake, or suspect it has been bitten, you would do exactly as you would do for a human. Get your vet ASAP or sooner. The problem is 99.9% of the time you don't actually see it happen.
What you often find is a horse that is looking weak or collapsed and you've got to deal with that. Could it be a snake bite? Could it have been kicked by another hose? Could it have an injury to its back? Is it a 'wobbler'? Has it got into some other form of poison? ( have you sprayed any poisons around?, have you been spraying insecticide?) There are so many things it could be.
The most common snakebites are browns; you get an occasional tiger and occasional red-bellied blacks. Red-Bellied Black snakes don't usually cause death, but they can cause a lot of pain & muscle damage & some blood changes.
The snakes that definitely cause death are the various brown snakes, King Browns, Taipans and Death Adders: there are a few of these in some areas, and there are a few Tigers around the creeks.
The take-home message is : IF YOU SEE YOUR HORSE GET BITTEN BY A SNAKE CALL THE VET NOW!
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