Not bad for a first story. You asked for constructive criticism, so let's start.

Firstly -- what is the character's name?

Secondly -- and I am almost a hypocrite to tell you this -- you need more details. Take a look at the first paragraph. There is an ad for a farm job in the paper. The main character sees it and applies. Okay. The story skeleton is there, but the paragraph is, to put it bluntly, boring. How did Josh find the ad? What is his initial response to the ad, and why does he choose to apply for the job instead of waiting for the next opportunity to come around?

You may have heard the phrase, "Show, don't tell." This means, instead of informing the reader of events through summarization or even description, communicate what you want the reader to know through the character's senses, thoughts, and words.

This would also resolve the problem of the character acting so passively to what's going on around him. Shouldn't he be the least bit surprised that he's accepted after a non-interview lasting four minutes? Maybe he could have asked why the "favorite animal" question was there. Why does the character just take what's coming to him in the lab, without wondering what's going on? How would he have lost his mind? Why does he decide to keep it? What are his thoughts about the whole thing?

We don't know, because the story doesn't say.

I'm confident you can and will improve. It takes practice.

Well it seems LeviWolstrom said it all pretty much, albeit a bit harsher than I might have. I do have a quesiton as well. The paper said it was a 15$ an hour job right? So that means legally speaking he should get paid. I would suggest that next time you try to add in something like an option to return to human form again after he's done working for the season or however long his new "employment" will last. Seeing as he chose to keep his mind. And if he chose to lose it, it probably would be good to have a serum that would turn him back and restore his human mind once the work was finished. Perhaps you could include some details of the jobs he did on the farm and how he lived, etc. And like Levi said before try to have a little more character interaction; a good conversation works very well to liven up a story and add content and depth to it. Plus it would be good to occasionally type from your character's perspective on what he might have been thinking or what sensations he experienced as his body changed. For example, a prickling when the fur broke through the skin or an odd numbness in his fingers as they melded and changed into hooves. That sort of thing. This story really isn't bad for a first try and I'm sure you'll only get better with time. Just try to remember those little details next time. Do that and I'm sure your next story will be great.