Does liver or kidney failure usually have to come from a reaction to medication or a toxin (ie a weed or chemical spray)? I am wondering as I just heard that a horse was found dead a day after suspected kidney/liver failure symptoms. They are doing a necropsy, but I was wondering what causes the failure? The horse was 14, never a horse in real work (a much loved pet) lived outside most of the time, very little grain very little stall time. I don't think it could be from receiving any meds because I had not heard about her being sick and needing any before hearing about her being sick yesterday. I wish I had more details but I am worried that maybe she got into something? There are other horses out in the field that all seem fine right now. I am just helping out my friend make sure her horses are safe out there. Thanks.
They are two entirely separate organ systems, and each is vulnerable to a whole variety of things that can cause the system to go bad. Leading the list for liver "failure" (a very imprecise term) would indeed be toxins, which can include medications, plants, pesticides, herbicides, poisons, sometimes in rare cases viral infections can damage the liver, too. Renal (kidney) "failure" (again the term is sort of nebulous) can be caused by profound dehydration, tying up, drugs for sure (especially NSAIDs like bute or banamine), major trauma, circulatory problems, congenital diseases, obstruction to the urinary tract, or just plain old age.
You are missing about 99% of the facts needed to speculate much, unfortunately.
I am not a DVM but I can assure you that there are many reasons for liver/kidney failure other than toxins.
What I can think of:
infection of the reproductive track
damage to a kidneys
drug reactions, such as from Antibiotics
Viruses and bacterial disease
Diseases of the veins in the liver.
Metabolic disease. Rare
Of course, toxins but that could include mushrooms and posionous plants as well as bad hay
Also, of course warfarin (rat poison) would cause liver failure. If someone put out rodent bait...