Carcass traits are moderately to highly heritable. This means that the carcass characteristics of breeding stock will be passed on to the progeny much like birth weight or average daily gain. Research indicates that there is as much variation within a breed as there is between breeds. In other words there are probably just as many Angus cattle that do not marble well, as there are Angus cattle that do marble well. In order to remain useful to the commercial beef industry, seed stock producers must identify genetic lines that will not only be reproductive, sound, and efficient but also those that produce a carcass that will meet industry standards.

In the past (and present), progeny tests are utilized to evaluate the carcass merits of seed stock cattle. This process is a very precise and accurate way to decipher the carcass value of a prospective herd sire. Progeny tests also prove to be very expensive and take a long time to collect significant results. Problems associated with direct measure of carcass quality, motivated the search for evaluation of carcass traits on live cattle and thus created real time ultrasound evaluation of carcass traits. Currently ultrasound measurements taken on yearling heifers and bulls are rib fat, rump fat, rib eye area, and intra-muscular fat. Ultrasound technology is a valuable tool for seed stock producers interested in improving the carcass merit of his or her herd.

The Canadian Angus Association endorses Centralized Ultrasound Processing (CUP) developed at Iowa State University. Data collected through CUP will contribute to body composition EPD’s comparable with the American Angus Association and Red Angus Association of America (once the joint run is complete**). Adjustments and ratios are currently available through the CAA on cattle who have been scanned using CUP. As stated before, there are four measurements taken in real time ultrasound, here I will explain them in detail;

*Definitions are provided by Becky hays Walter & Associates, Inc. d.b.a. The National CUP Lab & Technology Center*

Rib Eye Area (REA)

This image tends to be the most difficult to collect and requires the most highly skilled interpreting technician. The rib eye or longissimus dorsi, is the largest muscle in the body, and thus give an indication of the overall body muscling.

Because muscle is related to size, often the largest animal in the group has the largest rib eye. However, if there is an adjustment for age or ratio you can determine which animal is more muscular and which is simply just heavier.

Rib Fat

An external fat measurement taken between the 12^th and 13^th ribs – the location the carcass would be split into quarters in the cooler. Both the rib fat and ribeye area measurements are taken from the same image.

Rump Fat

An external fat measurement taken from an image collected between the hooks and the pins of the animal. Reported in inches, in most cases, an animal will exhibit more fat over the rump than the rib due to the physiological process of “laying down fat”. Therefore, more variation is often displayed in the rump fat measurements of a contemporary group than the rib fat.

The fat measurements (rib and rump) are used to determine overall external body fat. The external body fat influences the lean meat yield of the animal. Lean Meat Yield is calculated by the Canadian Beef Grading Agency (CBGA) and is an estimation of the percentage of the carcass that is red meat. Any carcass that is graded as Canada Prime, AAA, AA or A is also assigned on of the following Yield Grades:

            Yield Grade              Estimated Yield (%)
            Canada 1 (Y1)              59 or more
            Canada 2 (Y2)              54 to 59
            Canada 3 (Y3)              53 or less

Intra-Muscular Fat (%IMF)

This measurement determines that amount of fat within the muscle. Reported in “%”. This measurement should be collected when cattle are maintaining a high level of nutrition. The field technician collects four images and the values generated by the interpreting software are averaged for on overall % IMF.

Marbling is the percentage of intra-muscular fat as assessed by Canadian Beef Grading Agency employees. The range of marbling viewed by graders ranges from abundant, trace, slight, small to void. This marbling score in addition to other factors such as age, muscling, color and texture equate to the grade names we are all familiar with (Prime, AAA, AA etc).

Practical Application

Selecting cattle based on carcass traits can have an important impact on the end product. A study completed at the University oaf Nebraska in 1994 evaluated two groups of calves. Group one was calves sired by bulls with high marbling EPD’s. Group two was calves sired by bulls with low marbling EPD’s. The results (shown below) plainly show the bulls with the high marbling EPD;s  out performed the low marbling EPD bulls with all other conditions constant.

                        Group 1          Group 2          Group 1          Group 2
                        Steers             Steers             Steers             Steers
%Graded            77                    47                    72                    47

Choice

The beef industry is changing by providing economic incentives for producers who focus on quality rather than commodity pricing. Increased value based on marketing such as branded beef programs and grid-pricing of cattle are all driving home the importance to focus more on carcass traits than what has been done in the past. It is important for the seed stock industry to change as well, by developing carcass EPD’s and selecting genetic lines that will conform to industry benchmarks.

Jane Caine
Breed Developent
Canadian Angus Association

Misc Ultrasound Terms

LMY
Lean meat yield

Intramuscular Fat (IMF)
A measure of the % fat in the ribeye muscle (Marbling)
% Intramuscular Fat to Marbling Score Conversion
Percent Intramuscular Fat                     Quality Grade
Less than 3.0%                                           A
3.0%-3.9%                                                 AA
4.0%-9.7%                                                 AAA
Greater than 9.8%                                      Prime

Bulls will register less marbling and less backfat thickness than steers of the same genetic make-up on the same feeding program.

Rump Fat
Measurement taken of the depth of fat just over the rump.

Rib Fat
Measurement taken of the depth of fat over the ribeye muscle.

Ribeye Area (REA)
The area of the ribeye muscle at the 12th rib.