Umm, only with difficulty. See https://www.quora.com/Can-kosher-observant-Jews-go-hunting-and-just-use-tranquilizer-darts
Should I mention that my dog loves those dried meat strips? I'm afraid we'll start a chain of emails.
Is there another verb for dehydrating if we're specifically talking in a medical sense or is it just this one? I was confused when I saw that as an answer because I guess I assumed the horses were wet and were drying their coats/manes as they walked. Dehydration never crossed my mind though to be fair that's also a potential meaning for dry in English but eh... It's uncommon and if someone says they're "dry" in English they probably mean thirsty whereas dehydrated is a little more extreme. But maybe I'm overthinking or being overly medically minded? If I'm making flashcards though, should I add "dehydrating" to my flash card for this verb?
You can bring a horse to water, but you can't make him drink. Except, that is, if you walk him until he's thirsty. That's really what they're trying to say here with "dehydrating the horses". One wouldn't ordinarily say that in English. One might say they're "sweating the horses". And the horses overheat. They then lather and froth up. So they need to be cooled down with a long slow walk, followed by a lot of brushing.
As a native Hebrew speaker, I was a bit puzzled by the Hebrew sentence. In the discussion I saw the interpretation of "dries out" (the initially-wet horses), which makes perfect sense. For "dehydrates" it's correct, but not very natural. In the medical sense, we barely use the transitive מייבש. We say מיובש for the condition of dehydrated, or התייבש for having suffered dehydration, but talking about the cause of it is so rare, that if we do want to say it it would be more natural to say something longer, like הדרך הארוכה גרמה לסוסים להתייבש.
Actually, a fun slang interpretation sprang to my mind. There's a current slang לייבש meaning "to bore" - הרצאה מייבשת, or התייבשתי שעה בתור לרופא (not sure that one can be translated very well; it would be bored and/or annoyed from the waste of time). So the sentence would mean "the long road bores (and annoys) the horses".
What is the sentence meaning? Are the horses getting thirsty or drying off? In English we would say the horses are getting dehydrated, but if you are dehydrating the horses... well that sounds like they are meat becoming jerky. So do they mean "the long way is making the horses become dehydrated"?
If you are in Israel which is mostly desert and you get ill and the Dr. tells you that you are dehydrated you would want to know how to say that word. If you are thirsty and not dehydrated you would probably say I have a thirst or something like that etc. or one would say that to you unless they were worried that they were getting dehydrated. Either way I think that particular word even for beginners can be useful.
It is really an interesting question why it's "aruka" and not "arucha".
The hard bet is easy. It always has to do with mishkalim or the binyanim. מייבש is pi'el and in pi'el the middle letter gets a dagesh, so vet becomes bet, fey pey and chaf kaf. This can be seen when observing the same root in pa'al and pi'el. Here are some examples:
x ספר safar in pa'al and סיפר siper in pi'el
x שבר shavar vs. שיבר shiber
x בכה bacha vs. ביכה bika
But as far as ארוך, I see it's not consistent. Other examples from the same mishkal are רטוב, קרוב and צהוב. Here, צהוב acts the same way, feminine singular צהובה is tzehuba, but רטובה and קרובה keep vet - retuva and krova, respectively. (Although pealim lists both retuva and retuba, when I asked some native Israelis, they say they have never heard anybody say retuba, only retuva).