A.R. Crane*¶, R.R. Redden*, and C.S. Schauer¶
*Department of Animal Sciences, North Dakota State University, Fargo, ND¶Hettinger Research Extension Center, North Dakota State University, Hettinger, ND
Yield and quality of the lamb carcass are what ultimately determine the value of a lamb. The carcass evaluation system is used to evaluate the carcass merit of 4-H club lambs using data from ultrasound scans. Lambs are first weighed, given aleg score, and loin muscle eye area, fat thickness, and body wall thickness. The latter three measurements are determined by ultrasound scanning between the 12thand 13thribs. All of this data will then be used to evaluate the carcass merit of individual lambs.
The ultimate value of lamb is determined by carcass quality,with many factors playing a part in its evaluation. Ultrasound technology allows for the objective estimation of carcass traits in real-time of live animals (Grainer, 2001). This technology is important for the genetic improvement of carcass merit and is certainly an important tool for outreach to 4-H participants. Ultrasound measurement allows an opportunity to quantify conformation in an objective manner (Greiner, 2001) allowing lambs with superior carcass quality to be recognized through the ND premium lamb certification using the carcass evaluation live lamb index.
Determining Carcass Character. Carcass traits used to evaluate lamb carcasses are based on industry standards for dressing percentage and ultrasound measurements of fat and muscling.Hot carcass weight and dressing percentage:The weight of the carcass after slaughter is referred to as hot carcass weight. The relationship between live weight and hot carcass weight is called dressing percentage, which is figured by dividing hot carcass weight by live weight. For lambs, the dressing percentage can vary between 45 and 57 percent. For this evaluation, we used a value of 54 percent, which is based on research data from club lambs. For example, a 150-pound lamb is estimated to have a hot carcass weight of 81 pounds (150 pounds x 54 percent).Backfat thickness:This is the thickness of the fat from the ribeye muscle to the outer surface of the carcass measured at the midpoint of the ribeye muscle at the 12th rib location (Figure 1). Backfat thickness is the only factor used in the assignment of yield grades. Figure 1 illustrates the location of the backfat measurement over the center of the ribeye, between the 12th and 13th ribs. Fat thickness may be adjusted up or down to account for unusual fat distribution at the point of measurement. Backfat on carcasses usually ranges from 0.1 to 0.5 inch.
Body wall thickness:This is a measurement across the lean, bone and fat of the lower rib 5 inches from the midline of the carcass (Figure 1). This area accumulates excess fat in some animals and is an indicator of expected trimmed cut yield from the carcass. Body wall thickness usually ranges from 0.5 to 1.2inches.Ribeye area (REA):This is an objective measure of muscling in lambs and is measured in square inches between the 12th and 13th ribs (Figure 1). REA measurements usually range from 1.5 to 4.0 square inches. REA is affected by the weight and muscularity of the live animal and provides a good estimate of the percentage of lean to bone in the carcass.USDA yield grade:U.S. Department of Agriculture yield grades are calculated by using the following formula: YG = 0.4 + (10 × adj. fat thickness). USDA yield grades (1, 2, 3, 4, 5) categorize carcasses into groups according to the expected yield of trimmed, retail cuts. Yield grade 1 has the highest expected yield and 5 the lowest. For example, a lamb with 0.15 inch of backfat will have a USDA yield grade of 1.9 (0.4 + (10 x 0.15). Table 1 describes the assignment of yield grades based on backfat ranges and the average yield of semiboneless cuts for each yield grade.
Leg scores (Figure 2):These are used to evaluate muscling subjectively. Variations in leg score do not affect yield grade but are used to evaluate the attractiveness and lean yield of the lamb carcass. Leg scores usually range from 15 (very thick muscling) to 9 (thin muscling). A leg score of 12 is considered average for lamb leg muscling (slightly thick muscling).
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Please download the entire article for complete information. Although this was a test on lambs, they are very similar to goats.
Alison Crane will join us at the Midwest Buck Sale in June, 2021 for a class on learning how to ultra sound and the value it adds to your herd. Sign up will begin fall. Class size will be limited. Watch for more details.
Dr. Alison Crane
Sheep and Meat Goat Extension Specialist
Assistant Professor, Kansas State University
126 Call Hall