Ollie,
Enjoying the chat hope I don't stray to far.
To restrict the conversation strictly to timelines I would still have to say no that ultrasound would not improve the ability to speed up the process in determining a decrease in Warner Bratzler shear force measurements however it could affect the timeline on deciding which progeny are exhibiting an advancement in marbling.
If I am thinking correctly it would seem that we are presented with two totally unrelated variables, marbling and Warner Bratzler shear force measurements. Assuming that the original strength of muscle tissue is a component of and created by the Primary Structure (Atoms), the secondary structure (Molecules), the tertiary structure (The way molecules interact with themselves and others by folding towards positive or negative charged particles within that molecule) and quaternary structure (Multiple molecules forming complex tissues) it would seem reasonable that marbling is an extracellualr factor rather than an intracellular factor. In other words marbling is fat cells interspersed between the muscle cells and not actually part of the muscle so the muscle integrity is not compromised. One could reasonably assume that this dispersement would cause a weakness in the integrity of the overall strength of the muscle which would lead to decreased Warner Bratzler shear force measurement, however from what I have read this is not true. I believe the reason for this is that the test does not consider a given mass of muscle but rather the entire muscle that is tested (Could be wrong) Consider the following article:
Use of Expected Progeny Differences for Marbling in Beef: II. Carcass and Palatability Traits
B. L. Gwartney, C. R. Calkins, R. J. Rasby, R. A. Stock, B. A. Vieselmeyer, and J. A. Gosey
Department of Animal Science, University of Nebraska, Lincoln 68583-0908
ABSTRACT A 2-yr study was conducted to determine the effect of EPD for marbling on marbling score, palatability traits, and carcass fatness in beef. Steer (n = 122) and heifer (n = 123) carcasses were obtained by mating Angus bulls having a high (>.4) or low (<-.16) EPD for marbling to MARC II cows (¼ Angus, ¼ Hereford, ¼ Simmental, and ¼ Gelbvieh). Carcass traits, composition of primals, quarters, and sides, palatability, and shear force data were obtained and adjusted to the mean number of days on feed, equal marbling score (Small50), fat thickness (1.0 cm), and carcass weight (318 kg) end points. Steer carcasses from the high marbling EPD group, adjusted to the mean number of days on feed, had significantly more marbling (P < .01) and less subcutaneous fat in the side and the hindquarter (P < .10) than their low marbling EPD counterparts. Adjusting steers to Small50 marbling produced smaller longissimus muscle area (by 5 cm2), less fat thickness (1.15 vs 1.28 cm), and lighter side weights (306 vs 333 kg) for high marbling vs low marbling EPD groups, indicating a faster rate of marbling deposition. Similar relationships of a greater magnitude were found for heifers, perhaps because the heifers were older than the steers at slaughter. No differences in taste panel ratings or shear force values were noted among steer carcasses. Heifer carcasses from the high marbling EPD group had better (P < .05) ratings for juiciness, muscle fiber tenderness, and overall tenderness than the low marbling EPD group heifers. These results indicate that it is possible, using existing genetic resources, to maintain marbling score and decrease fat in other depots of the carcass without compromising palatability.
So marbling may or may/not be related to Warner Bratzler shear force measurements but obviously could be picked up by sono which could speed up the breeding process.
Originally I postulated a correlation between the reversal and breakdown of the hierarchy of at least quaternary and tertiary structure through the degradation of tissues via enzymes. Simply put it was created by a chemical reaction and thus it can be reversed with a chemical reaction.
Once again I would speculate that it has more to do with a Primary structure composition (Individual molecules making up compounds) as opposed to a Quaternary composition (Groups of Molecules forming tissues/organelles). Consider this, collagen is a compound that gives connective tissues, including skin and muscle additional strength, and the blue Belgian, a double muscling breed (Thank you guest for your clarification on Double muscled cattle breeds) is known to have a deficiency in this molecular compound as well as a favorable Warner Bratzler shear force measurement. So one could perform muscle biopsies on progeny early on and perform Western blot Assays (Testing looking for specific molecules) it seems reasonable that the process could be sped up as well. Keep in mind that with a deficit in collagen an entire host of problems comes as well.
The web page to the following article seems to indicate degradation in the calpain/calpastatin system after freezing of carcasses even when there are variables in the equation such as marbling. Hence one could assume that marbling was not a contributing factor for Warner Bratzler shear force measurements but rather a break down in the ability of the enzyme Calpain to function after it was frozen. Another words the freezing could have denatured the proteins (destroyed the physical structure) of the enzyme thus rendering it ineffective. Enzymes function much like a key that fits into a lock, if you denature the enzyme (Extreme heat, cold, Ph changes), or in simpler terms bang on the key with a hammer, it no longer fits in the lock. If the Key no longer fits in the lock the chemical reaction, which breaks down the dead or dying muscle tissue, will not occur by this process.
http://ars.sdstate.edu/extbeef/Publications/Journal_Articles/Shanks_JAS_2002_80_2122.pdf
As a final thought perhaps once you have identified the traits you desire you could utilize a different animal model to run your progeny testing. Something with a shorter breeding cylcle and perhaps a shorter life span will give you a higher number of progency to test for the outcomes you desire, most mammals carry similiar genes, molecules and enzymes.
