Wow, horses are not the main source of Clostridium tetani, they live everywhere including in soil. Of course a horses intestines would have some there as well but still...
You are correct that rusty nails are not the cause of tetanus, that is in fact the aforementioned Clostridium tetani. However they are an ideal breeding ground for them as the bacteria prefer dry anerobic environments like your average rusty nail. However a non rusty nail on the ground would also be another great source for them, really anything that can puncture the skin.
Again, this bacterium is everywhere and has nothing unique to do with horses or their manure. Tetanus toxin is an extremely potent and life threatening neurotoxin. Ascorbic acid will do nothing to change its function, nor will it treat the infection were someone to become inoculated with Clostridium tetani.
I am quite thankful that Dr. Klenner is not my doctor, nor would I be stupid enough to seek out his medical advice. What do you call a doctor who graduates last in his class? You call them doctor.
Here is a copy of Dr. Klenner's paper on Vitamin C & Tetanus, published in the Tri-State Medical Journal in 1954.
http://www.mv.helsinki.fi/home/hemila/CT/Klenner_1954_ch.pdf
While he did believe in vaccination, he found a way to treat people who had Tetanus. You know that the Tetanus Vaccine is nowhere near 100% effective anyways -- so why wouldn't you want to seek out a doctor who has had success curing it if you ever did get Tetanus?
The above article is not an acceptable justification of much of anything. There have been other articles also discussing this idea, however no well done study has ever been performed as of yet.
https://www.ncbi.nlm.nih.gov/pubmed/184259
"A single, non randomised, poorly reported trial of vitamin C as a treatment for tetanus suggests a considerable reduction in mortality. However, concerns about trial quality mean that this result must be interpreted with caution and vitamin C cannot be recommended as a treatment for tetanus on the basis of this evidence. New trials should be carried out to examine the effect of vitamin C on tetanus treatment."
I remain unconvinced. Additionally your stance against vaccination is without scientific or medical justification, so your opinions on this matter are clouded with bias.
Even the CDC says this about Tetanus: (Note that horses is first on the list.) "It is more common in hot, damp climates with soil rich in organic matter. This is particularly true with manure-treated soils, as the spores are widely distributed in the intestines and feces of many animals such as horses, sheep, cattle, dogs, cats, rats, guinea pigs, and chickens" (I found it on Wikipedia)
Of course the bacteria live in the intestines of animals, they bacteria live in the ground, and animals spend their whole lives outside eating things off of it. I mean this isn't rocket science here. And of course using the manure from those animals would result in concentrated pockets of the bacterium and its mature spores. That does not mean they are the only source for it. It is in fact, quite widely distributed, in the soil. You don't need animals for it to be present, as your earlier statements quite blatantly state.
I don't care to attempt to convince you of anything personally. That is quite clearly a waste of time.