%IMF or Marbling Score…Which is it? How can I tell?
by Patrick Wall, Director of Communications, The National CUP Lab
American Chianina Journal
With all of the incentives to raise Choice and Prime cattle, it’s easy to see why so much selection pressure has been placed on marbling. However, the industry has done a poor job of explaining how producers can use ultrasound to select for quality grade, how ultrasound “measures” marbling, and why it’s done in such a confusing fashion. Percent Intramuscular Fat, or %IMF, is the common ultrasound term for marbling, but it needs further explanation to fully understand the concept. In short, %IMF is simply an indicator trait for marbling, much like Birth Weight EPD is an indicator of calving ease. With high marbling EPDs and carcass quality genetics demanding top dollar in the sale ring, it is extremely important producers understand what they are buying.
The major difference between %IMF and marbling is that %IMF is a numeric objective measure, whereas marbling is subjective to the eye of the grader. The correlation is usually around +.70 to +.80 between the two measures. In order to accurately predict USDA marbling score using ultrasound, the same grader would need to be used for every research trial. As a result, a chemical extraction procedure was adopted, using the percentage of intramuscular fat in the ribeye muscle. The collection of %IMF comes from taking a thin slice of the ribeye in the cooler. External and seam fat are removed from the sample. The steak is then frozen, ground up, and ether extract analysis determines the fat percentage from a sub-sample of the ribeye. Thus, a live animal with an ultrasound estimate of 4.0%IMF should also produce a carcass with a ribeye steak that has 4.0% fat within it.
