They also have a genetic defect know as HYPP that caused the death of a lot of really expensive halter horses.
Any time you breed genetics that are v ery similar together you will exponentially mulitply the genes present-- good and bad.
The scary thing to me are the genes that don't show up in the phenotype(physical appearance or traits) of the animal so we don't know they're even there.
Many of the undesirable traits we cope with today were caused by just such matings that produced outstanding looking (possibly even extreme in some cases)animals that were hiding undesirable traits we couldn't see but became very apparent in future generations.
i'll quibble a little bit here. if they linebred impressive, they would have found out a lot quicker about hypp. same with herda.
i personally would rather breed to linebred animals, as this maximizes visualization of hidden genes quicker, and if culled, is much faster to get rid of them rather than creating ladies in waiting. linebreeding used to be somewhat routine by design. nowadays, it's almost unavoidable to breed closely not by design, as those heatwave females accumulate.
it's true that many undesirable traits we cope with today are a reuslt of "such matings". linebreeding will be the fastest way to get rid of undesirable traits completely from the gene pool, other than genetic screening.
here's a subset of my ideall starter herd for purebred maines which i didnt' do, but wish i had.
they all have issues, but linebreeding seems to have moderated them in some very outstanding individuals. i guess that's a lot of individuals for linebreeding, but they do have a theme, and not necessarily the touchstone. i would like to see a lot more half sib matings in the maine breed. probably one of the faster ways to get consistency, but not necessarily dramatic progress.