Is that a contraction both ways of ένα? We've seen the ε drop out after είναι but is the α dropping out before άλογο too?
No vowels are dropped in the audio, each of the identical vowel sounds (είναι ένα άλογο) is simply uttered in two beats, like a long vowel sound. The audio is very good for this sentence as it is written, without the contractions. It's just that there are no breath breaks between the fully pronounced words. The contracted vowels sentence would be Αυτό είν' έν' άλογο with shorter vowels where they have merged.
It is really fun doing the listening exercises with a hearing problem. The word άλογο completely sounded like ελέφαντες to me because my hearing aid makes things louder but not clearer. But I do my best.