Great concept and a lot of fun to play once I figured it out! I just had trouble at the start because the tutorial showed one kind of sick sheep, so that's what I was looking for. Then, when I lost the first... 10 times, haha, I didn't know which sheep on the screen did it. Maybe the game could've spent a second pointing out the offender.
Also, nothing to do with the gameplay - when you're doing pixel art, watch out for mixels! That means mixed /different sized pixels on the screen at the same time.