After you get over the initial shock, you find that it really doesn't matter if you are a mare or a stallion. Heck, you could have been a gelding! After becoming an animal, a simple sex change isn't that big a deal.
The boy returns with oats and fills your water bucket, and then leaves you alone again in your stall. Oats taste good, better than you thought they would. The scents and sounds of the stable are new and familiar at the same time, and you find yourself drifting off into a sort of half-sleep until dawn the next morning.
Before the sun is fully up, you have been brushed and fed, and are being led back outside the barn by your master. He takes you to large field and positions you in front of a big plow. It is about halfway across the field, where you stopped yesterday. He hooks you up, and after a couple of false starts, you are pulling the plow behind you.
The steady, plodding work is almost second nature to you - horse thoughts are very simple and relaxing. In a way, you rather enjoy the feeling of strength and mass, the powerful thrust of your muscles as you work. By the time the sun is going down, you have almost finished the field. The boy has given you a few breaks, and fed you once. Still, you are tired and hungry when he takes you back to the stall.
The next few weeks are so similar it is hard to count the days. Sometimes, you are used to plow. Sometimes you pull a wagon. And some days you get to relax and graze in the pasture.
It has been a long time since you became a horse when the boy rides you to a big pond where his buddies and he all skinny dip. There are other horses and a donkey there, all grazing peacefully in the field by the pond. You are happy to be with the other equines, and find them to be very friendly to you. The donkey and a big shaggy draft horse seem VERY interested in you.
You can tell from their scents that they are both males, and it is obvious they have mating in mind. What is also suddenly obvious to you is that you are in heat! You want one of them! The boys point and laugh, even your master grinning as the two males circle you.
The horse part of your mind wants to mate, but the human buried deep inside is worried. What happens if you get pregnant? Can the barber change you back anyway? When will he be coming, anyway? He said a month - but how long have you already been here.
Well, he changed you back before, he should be able to do it now. And you are really curious about what mating is like.