The individual sounds seem to be taken from some longer recording. In my experience, the Italian accent leaves the tongue very far forward - on the teeth- on certain word endings, in this case, "un." The result is a release of air while the mouth resets from "n.". When slowed down, this effect is exaggerated. Listening to "un" and "una" side by side, the difference is apparent, as the "-a" sounds much more deliberate. Seems to be just a sloppy editing job.
To all those complaining that the slow version is incorrect: Italian is not spoken as in the slow version. Never. That's just a learning aid for you. So saying that it is unfair because it is pronounced in an odd way is like saying that it is unfair that Italian has a different grammar than [insert language here] :-)
As a general rule, nouns and adjectives ending in -e in the singular end in -i in the plural, regardless of gender (il cane, i cani; l'arte, le arti; l'otre, gli otri; la parte, le parti); of course there are a few exceptions.
As for animals' gender, not all of them have a grammatical one matching their biological one; just like in English there is a male lion (leone) and a female lioness (leonessa), but only one word for tiger/tigress (tigre, feminine) regardless of its gender.