Larry, after doing a bit of research I find that most lamb sausage recipes call for grinding lamb that has been only minimally trimmed of fat. Overall lamb sausage is a fairly lean type of product. When a recipe does call for added fat it calls mostly for pork fatback at about a 20% ratio.
As much as I like lamb I have never made lamb sausage and might give it a try sometime soon. The information here is from my recipe archive and not from personal experience with making that type of sausage. Hope this helps!