Yes that is very true. Outcrossing is the way to go to strengthen the
species; it is called Hybred Vigor. A great breeding program, in my
opinion, consists of breeding animals who are line bred. Breeding two
line bred individuals (who are not related) will produce offspring that
are "stronger, taller, more vigorous" than the parents. Looking for a
champion performance prospect?, look for a horse whose parents come from
two different lines. Obviously there are exceptions, but that formula
will work for breeders who want to produce performance animals.
Lauren