At first, there was one tenderness factor discovered -
calpastatin - and that test was patented by the Australian
GeneStar people. Later MARC released another factor to
the public, calpain, which is for an enzyme that aids in
tenderness during the ageing process. So at that point,
the GeneStar people had 4 "stars" as a perfect tenderness
score. They sold the N.Amer rights to calpastatin to
Bovigen, of Louisiana.
I obtained a breed comparison chart from GeneStar before
they sold to Bovigen. This is when 4 "stars" was a perfect
score:
You will note that Murray Greys have the highest percentage
of one and two star animals among the breeds tested. Only
those breeds with more than 100 animals tested were included on the chart.
Now MARC has released another newly discovered factor;
so the perfect score is 6 "stars". They will not now(and
probably never) release another breed comparison chart
because the one shown above made some Angus breeders
mad(Bovigen is owned by angus people) and really really
made the hereford people mad.
Our murray grey herd bull that we sell semen from has a
perfect 6 star score, as does his 3 yr old son. We are also
using semen from two other murray bulls, that also have
perfect scores.
Heredity/probablility
From a Gene Star brochure when they
had 4 stars as a perfect score)
If both sire & dam has the same score, the calf will also.
If sire has 2 stars and dam none, they show 100% chance
that the calf will have one star....
and so on.
You should write for their info packet/brochures to get
the full story.
We have decided not to use any bulls that do not have
a perfect tenderness score---because we sell beef.