ermm... i'm going to try and play know-it-all here. by "thin," he means blade width. you don't slit a livestock's neck across as with people. you stab the neck to reach the jugular. i've seen this with hogs and cattle. hogs have thick fatty necks so the blade goes far in. with cattle, the hide is tough and the jugular is also far in. the only livestock you can slit near-superfically are fowl.
therefore, you need a blade at least 7" long, pointy, thin (less than 1 1/2 inch width), with good finger guards (your hand can disappear inside the carcass,) and sharp enough on the upsweep end to cut arteries inside.
hope i got the requirement right.