TSR: I don't post alot, but I am interested in this genetic testing for marbling and tenderness. They can, by using shear force measurements, detect the difference in tenderness between a 4 and 6 star animal, and should be able to detect the difference between 5 and 6 star animals. There are genes that affect tenderness that may not be identified yet, so I don't know that the difference would show between every 5 and 6 star animal, but given a population of them, there would be, to my understanding, an avg. of .5 lbs of shear force difference between them. To answer your question, according to the testing, one would expect a 1 lbs difference in shear force between a population of 4 and 6 star animals.
Can the consumer, find that .5 lbs or even that 1 lbs. of difference? Good question, but maybe a moot point. We had a guy discussing grain marketing once that told me there were two things the market paid attention to: reality and perception. Focus too much on the reality of things, and perception is bound to bite you in the butt. I have found that to be applicable in all kinds of areas. So even if, realistically, consumers can't "taste" that .5 pounds, as long as "more genes = more tender," it is likely that someone, someday, could get paid for having more of them. It is very similar to the CAB program. The power of CAB lies in the perception of it.
The difference between a 5 and 6 star bull is significant. Bovigen wants to get a program together within a year that actually pays for tenderness. Now some want to test for this tenderness using scanning, which is also still being developed, but the people that want to do it genetically seem, the last I heard, to be leaning towards animals that are guaranteed to carry three copies of the desired genes. They only way a producer could guarantee that, without testing each calf, is to show that the calves were sired by 6 star bulls for tenderness. These would be the only bulls that would be guaranteed to pass at least three tenderness genes to all of their offspring.