The Grimm alfalfa really made possible MN and WI dairy industry. I think most all modern strains of Northern Alfalfa are offshoots from the Winter hardy old Grimm.
I'm going to check into it, see if the original is still available.
The problem I see with the new varieties is that increased yield has been sought for at the expense of winter hardiness and longevity. A 'less root, more shoot' cause. You used to be able to plow down a field of Grimm and hear the snapping of the tap roots as you sheared them off. You might not be able to get a second cut on Grimm every year, but at least it stayed in the ground for more than 3 years. I have also found evidence on a neighbours farm where broadcasted Grimm (by birds) germinated...something people say you cannot do with alfalfa. :cowboy: