The Day the Cow Sneezed, written and illustrated by James Flora. 1957.
I had been looking for this book for a long long time and finally found one on eBay with a price that I could afford: $16! It was a former library book, but no marks or tears inside.
The cover you see here is not from my copy. Mine had those ugly library stickers covering the cow and spine. This cover image is courtesy of Flora's biographer, Irwin Chusid.
More about this book on my blog.