What is hold her newt she's a rarin' for the barn?

"Hold 'er Newt, She's a-rarin!" is a quote from a comic strip dating back to at least the 1930's. I do not recall the name of the comic strip, but it depicted a wagon piled high with all sorts of household goods and junk. Two men are sitting on top of the load and it's leaning precariously, while the horse rears back.