"Oh-vo-shet" is certainly curious, but I think I can see how it happened, and, in fact, you've stumbled upon a curious little feature of Russian pronunciation that even most native speakers aren't conscious of.
The "v" is explained easily, it's what the hard [ɫ] sounded like to you, being as it is quite different from the [l] in English.
But what to make of the "oh"? Without hearing the recording, I suddenly had a flashback to my childhood, when I heard a then-unfamiliar word, рафинад, and from the way it was pronounced by the speaker, wasn't quite sure whether it was that or "арафинад".
After a bit of self-testing for what sounds natural, here's what I have. When a word begins with a consonant that is voiced, non-plosive, and non-nasal (that's [в], [ж], [з], [j], [л], and [р]), and when that word begins an utterance or comes after a pause, sometimes there's a tiny prosthetic vowel in front of it; it doesn't come across as wrong or "uncultured" (in fact, like I said, it barely registers at all), so there's a chance that the Duolingo recording you heard had this ghost of a schwa, [ᵊ]лошадь, in front of it.
When we learn the phonetics of a new language, it's hard to tell the regular from the accidental, and it sometimes happens that native speakers don't seem to have an idea what you're talking about. Don't be discouraged. In fact, it's an interesting thing you've spotted there, albeit at this point it's probably not going to be very relevant to you as a learner.