I assume in UK horse is common animal on paths etc. But in other parts of the world, there are other animals used for both ridning and transportation. And maybe more common then horses.
How are these other animals defined in OSM?
I feel “horse” is too restrictive.
My understanding is that horse=* and highway=bridleway exist because horse riders are a particular legal category in the UK, and there are regulations about where they have the right to ride (and possibly where they’re not allowed to ride).
Tags in OSM are generally used on an as-needed basis: they’re used when there’s something that mappers want to describe, not when there’s something that possibly exists. Are there any other regions where regulations or laws for riding or leading specific animals are made? Like, donkeys being explicitly allowed along a particular trail, or not allowed on a particular trail? Llamas? Camels? Reindeer?
There is at least one trail in Rocky Mountain National Park (in Colorado, USA), that does not allow horses, but does allow llamas - at least according to signs along the trail. Note that llamas are generally not ridden, but are used for carrying supplies and gear.
I don’t know about trails, but some countries have standard traffic signs for restricting beasts of burden on roadways:
Some U.S. states have standard signs for prohibiting “animals on foot” from a freeway or expressway. This technically means animal=no but in practice means horse=no carriage=no. After all, truck trailers carrying horses are not only allowed but extremely common along these roads.
Historically, there were laws against leading beasts of burden across certain bridges. Local laws to this effect may still be in effect in some localities and even signposted, but it’s more of a curiosity than anything practical.
No camels or horses:
Incidentally, camel | Keys | OpenStreetMap Taginfo has 42 usages, including some in Oklahoma.
Only 3 for llama in the aforementioned Rocky Mountain National Park, 3 for alpaca and 1 for alpaka
Also 28 donkey=yes
So OSM is all set really 
Any tags you like - OpenStreetMap Wiki
In Germany, we have an official sign disallowing horse but by rule this means riding animals is not allowed which is tagged horse=no.
Additional, we have a sign disallowing carriage which is tagged by no surprise carriage=no.
Leading or herding animals is not affected by these signs.
Overall, we get into trouble if only riding horses is disallowed but riding other animals is allowed and choosing horse=* as access tag to disallow animal riding turns out to be a bad choice. Probably animal_riding=* would be better to even cover dolphins or turtles.
To me “horse” is restrictive. As we all know transportation of goods and people is done with other four leg animals then horses. I’m not sure if there is any desire to have keywords/taggs for other four leg animals.
Under England / Wales Rights of Way law donkeys and mules are classified as horses.
A bridleway allows horses/donkeys/mules to be ridden or led but not if they are pulling a trailer or carriage, that needs to be a byway or restricted byway.
If I came across a sign saying that $animal was allowed or forbidden on a road I’d probably just tag $animal=yes/no .
OSM tagging isn’t set in stone; if in the future people have to take account of e.g. camel=yes somewhere so be it.
Funny you should mention camels, Camels on bridleway - Viewing a problem :: FixMyStreet
For what it’s worth, the U.S. tagging guidelines also take the general approach of tagging more or less what the sign says, straining at times to translate American terminology to OSM’s British-inspired terminology. Thus “No Commercial Vehicles” becomes goods=no etc., even though the U.S. doesn’t recognize a vehicle classification equivalent to the European definition. However, the difference between New York’s “horses”, Kentucky’s “animals on foot”, and Ohio’s “animals” is extremely pedantic in practice, and horse=* is already such a common access key in OSM, so I think most mappers opt for horse=no.
Of course, this is all pretty hypothetical. I focused on streets because that’s what traffic signs are designed for, and I know how much importance this community places on prohibitory traffic signs. But any kind of vehicle or conveyance would have to be street legal in order to ride it in the street anyways. If someone is using a horse router for long-distance travel, they probably already know that freeways aren’t very friendly to horses – even in Kentucky, where racehorses are so popular that the authorities put them on as many traffic signs as possible – to say nothing of intercity llama routing. Restrictions about animals in general would matter somewhat more on parklands, where there are special rules for just about everything.
Your examples perfectly show the problem. Speaking about Germany, we have no access tag to disallow horses (or animals) besides highway=motorway and motorroad=yes. horse=* is about riding animals but does not forbid to lead or herd animals. Actually the same is true for bicycles and even motor_vehicles which are still allowed to be pushed. (We had some discussion about bicycles been forbidden even to push on a campus but I do not find it atm.)
Wouldn’t this be the difference between bicycle=dismount and bicycle=no? Admittedly it’s a little funny to say “dismount” if one hasn’t even mounted the conveyance in the first place, but at least that terminology is familiar to people who keep horses.
Pushing a car is normally something you’d do as a last resort. I don’t think there’s a need to encode an exigency like that as a normal access restriction. That is however my favorite misinterpretation of this sign assembly:
Unfortunately no and dismount are more or less equivalence, see Tag:bicycle=dismount - OpenStreetMap Wiki and Tag:horse=dismount - OpenStreetMap Wiki.
Yes, pushing a car is quite uncommon but a Fiat 500 can easily be pushed by a single person as long as it does not go uphill and how about small motorcycles or even mopeds and mofas?
The author of these pages explained their reasoning in response to a request for OSRM to route cyclists over bicycle=no as a last resort, similar to how it implicitly tells you to walk your bike on footpaths or against the flow of traffic. I would just point out that context matters: you necessarily have to get off your bike on a route=train, even if bikes are allowed on board, so bicycle=no can only realistically refer to transporting a bike. And when the signs literally say to dismount or not to ride a bike, people are going to tag that differently than when the signs only prohibit bikes ambiguously. They aren’t going to go there and test the waters by walking a bike right in front of a park ranger. Much the same is true of horses or any other conveyance.
The “Turn Off Engine” sign I posted is intended for bus operators. 
dürfte das gewesen sein.
I am the author wiki page Tag:horse=dismount and nowhere did I write that Tag:horse=no and Tag:horse=dismount are equivalent. Tag:horse=no simply says nothing about whether leading a horse is allowed or not and the router has to guess that if necessary; this is clearly some difference to Tag:horse=dismount. The fact that the latter tag is used much less (presumably because in public spaces horses are mostly ridden or driven and not led) does not change this.
Sorry to put words in your mouth; I meant to refer to @Mateusz_Konieczny talking about his authorship of the bicycle=dismount page.
Oh, diese Diskussion hatte ich völlig vergessen. Ich war auf der Suche nach einer Diskussion über ein Uni- oder Schulgelände, wo Fahrräder komplett verboten sind.
Trotzdem Danke für Deinen Link und Deine Mühen.
