Sheep Grading

Economically important traits for sheep evaluation that will be discussed are: 1) live weight; 2) dressing percent; 3) fatness; 4) muscling; 5) yield grade; and 6) quality grade.

Live Weight – Most lambs are marketed between 105 and 130 lbs.  Ewes and wethers are marketed at similar weights

Dressing Percent – Dressing percent is important because it indicates the proportion of live weight that is contained in the carcass.  Sheep have the lowest of the three species discussed and more variation based off of wool

            Dressing % = (Carcass Weight/ Live Weight) * 100

            It is affected by:

                        1. Fill

                        2. Finish – increase in fat will generally increase dressing percent

                        3. Fleece

                        4. Sex

                        5. Muscling

            Average – 54 %( shorn lambs) & 52 %( unshorn lambs)

            Range – 44-56%

Fat Thickness – is measured at the 12^th rib, and is the single factor used in yield grading ribbed lamb carcasses.

           Average- 0.25 inches

            Range – 0.05 – 0.50 inches

Body Wall Thickness – measurement taken approximately 4.5 inches from the midline of the ribbed lamb carcass.  A lot of variation exists for this measurement based mostly off of Age, Breed, and weight.

            Range – 0.60 inches – 1.25 inches

Loin Eye Area – is a cross-section of the longissimus dorsi muscle between the 12^th and the 13^th rib.

           Average – 2.3 inches²

            Range – 1.5 – 3.5 inches ²

Yield Grading – based solely off of measurement recorded opposite the ribeye between the 12^th and 13^th rib. 

            Yield Grade = (Back Fat * 10) + 0.4

            Example: 0.20 inches of back fat would be:       0.20 * 10 = 2.0 +0.4 = YG 2.4

            USDA 1 – Most desirable – minimum fat and heavy muscled

            USDA 2

            USDA 3 – Average

            USDA 4

            USDA 5 – Least desirable – fat and light muscled

Quality Grade – formulating a quality grade for lambs combines three separate factors that affect the palatability of the meat.  They are:      

            1) Maturity – insures that old or mutton sheep are not graded as young lamb.  It is determined by evaluating the joint at the bottom side of the cannon bone; whereas mature lambs develop a fused “spool joint” and young lambs possess a “break joint”

             2) Quality – The quality of sheep is evaluated by looking at intramuscular fat, much like in cattle, only this intramuscular fat is contained within the muscle of the flank.  As level of flank streaking increase, so does quality grade.

             3) Conformation – The unique portion of lamb grading is the inclusion of a conformation factor.  This insures that a carcass has a desired portion of red meat for its carcass.

   Grades for lambs include:

             Prime – Highest

            Choice – Most lambs

            Good –

            Utility –