I have neighbors who have a commercial angus herd of around 200 cows. They feed out their own steers and non-replacement heifers (on corn) and the animals go directly to Moyer and Taylor packers in Pennsylvania at around 14 months.They have over 20 years of carcass data and grade over 90% choice.
I help them a lot and know every cow they have that is part Shorthorn. There are about 20 and I know them by tag number. We were involved in a DNA study a few years ago, testing for marbling, tenderness and feed efficiency, along with about 400 other animals from smaller farms, representing many breeds from Devon to Charolais. My neighbors' cattle were the high scorers for marbling, primarily because of breeding to AI Angus sires strong on this trait. The cows tested would have been the retained daughters of those sires. I sorted that data to see who the top cows were for marbling, and then again for feed efficiency. The tag numbers that rose to the top 10% for marbling were the Shorthorn cross tag numbers. 20 out of 200, and of those 18 were the Shorthorn crosses.
The feed efficiency sort looked basically opposite to the marbling sort, with those animals near the bottom.
The tenderness scores followed marbling much closer than they followed feed efficiency.
The Shorthorn crosses they have were sort of thin skinned, hard doing sorts that required more feed to stay in condition. They bred back reliably, though, or they got culled.
The other top producer for marbling was a Charolais breeder who is about 80 years old. He has consistently selected for docility for about 40 years. His cows are pretty fat.
My guess is that there is some genetic synergy with Shorthorn and Angus that boosts marbling. Things can be linked in so many different ways that it's hard to imagine the whole picture.
The docility approach I think is a more straightforward way to get IMF.
Even if an animal tests high for marbling, will it marble? As usual, it depends...
