Sounds a useful piece of research and if it comes out to show that the natives have a greater vigour then the preservation of native breeds will be partially vindicated
as that trait can then be bred into some super-sheep.
I can see a skew already though: most native sheep lamb outside unassisted, and tend to lamb just before first light (when sensible folk are still asleep
) so most of the observed births are going to be those which are lambed indoors. There is a chance that flocks lambed indoors could have decreased or increased vigour after birth compared to those which are lambed outside, so first of all a piece of research needs to be done to test that. On the other hand, if the commercials being assessed are lambed indoors, then perhaps the natives should be under the same system too.
I think I'll contact Ruth to find out more