Raw Carcass Data

Lambs were harvested on August 8 at Old Line Custom Meat Company in Baltimore. Carcasses were evaluated on August 12. Carcass data was obtained from 64 lambs: 21 rams, 18 short-scrotum (SC) rams, and 25 wethers. The carcasses were split between the 12th and 13th ribs to expose the longissimus dorsi.

Group	No.	SLW	HCW	DP	BF	BWT	REA	CWT	KH	LC	YG	BCTRC
Ram	21	122.7	63.0	51.2	0.083	0.529	3.01	2.47	2.24	13.0	1.23	49.75
Short-scrotum	18	119.7	60.7	50.6	0.100	0.514	2.83	2.38	2.14	12.4	1.40	49.48
Wether	25	112.1	58.6	52.3	0.142	0.558	2.71	2.45	2.28	12.6	1.82	49.04
ALL	64	117.7	60.6	51.5	0.111	0.536	2.84	2.44	2.23	12.7	1.51	49.40

These are raw data. It is not known if observed differences are statistically significant.

Ribbed carcasses

Shrunk live weight (SLW)
SLW was calculated by multiplying the (final) August 7 weight by 0.96. SLW ranged from 88.1 to 152.4 lbs. and averaged 117.7 ± 14.3 lbs. Rams were heaviest: 122.7 ± 15.8 lbs. Wethers were lightest: 112.1 ± 12.7 lbs. SC were intermediate: 119.7 ± 12.3 lbs.

Hot carcass weight (HCW)
HCW was determined immediately after slaughter. For the 64 lambs, HCW ranged from 42.0 to 79.0 lbs. and averaged 60.6 ± 8.0 lbs. Rams were heaviest: 63.0 ± 8.9 lbs. Wethers were lightest: 58.6 ± 7.1 lbs. SC were intermediate: 60.7 ± 7.7 lbs.

Carcasses were weighed after chilling. Cold carcass weight (CCW) ranged from 40.0 to 76.0 lbs. and averaged 58.3 ± 7.9 lbs. Cold shrinkage ranged from 1.4 to 7.4 percent and averaged 3.8 ± 1.4%. CCW was not used in any calculations.

Dressing percentage (DP)
DP is the percent of live animal that ends up in the carcass. It was determined by dividing HCW by SLW. For the 64 lambs, DP ranged from 47.7 to 55.2 percent and averaged 51.5 ± 1.7%.  Wethers had the highest dressing percentage: 52.3 ± 1.6%. SC were lowest: 50.6 ± 1.8% Rams were intermediate: 51.2 ± 1.6%.

Back fat (BF)
A metal ruler was used to measure BF. For the 64 lambs, BF ranged from 0.05 to 0.25 inches and averaged 0.111 ± 0.046 inches. The median BF was 0.100 inches. Wether lambs were the fattest: 0.142 ± 0.047 inches. Rams were the leanest: 0.083 ± 0.029 inches. SC lambs were intermediate: 0.100 ± 0.034 inches.

Body wall thickness (BWT)
A metal ruler was used to measure BWT.  BWT is a measurement across the lean, bone and fat of the lower rib, five inches from the midline of the carcass. Differences in carcasses are due primarily to fat. For the 64 lambs, BWT ranged from 0.30 to 1.00 inches and averaged 0.536 ± 0.125 inches. BWT was greatest for wether lambs: 0.558 ± 0.137 inches. It was lowest for SC: 0.514 ± 0.125 inches. Rams were intermediate: 0.529 ± 0.103 inches.

A nice one

Rib eye area (REA)
A plastic grid was used to measure the area of the rib eye muscle (REA; 20 dots=1 in²). For the 64 lambs, REA ranged from 2.10 to 4.05 square inches and averaged 2.84 ± 0.38 in².  The median REA was also 2.85 in². Rams had greater REA than wether lambs:  3.01 ± 0.40 in² vs. 2.71 ± 0.37 in². SC were intermediate: 2.83 ± 0.30 in².

Adjusted rib eye area (CWT)
Rib eye measurements were adjusted to a common weight (100 lbs.). For the 64 lambs, CWT ranged from 1.73 to 3.83 in² and averaged 2.44 ± 0.38 in². Rams and wethers had similar CWT: 2.47 ± 0.32 and 2.45 ± 0.48 in², respectively. CWT was lowest for SC: 2.38 ± 0.32 in².

Percent kidney and heart fat (KH)
KH is a measure of the (internal) fat around the organs.  It was subjectively evaluated and expressed as a percentage of carcass weight. For the 64 lambs, KH ranged from 1.0 to 3.5 percent and averaged 2.23 ± 0.79%. SC lambs had the lowest KH: 2.14 ± 0.80 percent. Ram and wether lambs were similar: 2.24 ± 0.82 and 2.28 ± 0.78%, respectively.

Leg conformation (LC)
LC is another measure of carcass muscling. It was subjectively evaluated using numbers that correspond to USDA quality grades. For the 64 lambs, LC ranged from 10 (low Choice) to 15 (high Prime) and averaged 12.7 ± 1.3. Rams had superior LC: 13.0 ± 1.5. Wethers had slightly higher LC than SC lambs: 12.6 ± 1.2 vs. 12.4 ± 1.3.

Chris Anderson measuring back fat and body wall thickness

Yield grade (YG)
YG (1-5) reflects the quantity of "retail" cuts that can be expected from a lamb carcass. YG is calculated solely from BF using the following formula:  (back fat x 10) + 0.4.  Rams had the lowest YG: 1.23 ± 0.29. Wethers had the highest: 1.82 ± 0.47. SC were intermediate: 1.40 ± 0.34. The marketplace tends to prefer lambs that are YG 2-3. YG 1 carcasses may be discounted.

Percent boneless, closely trimmed retail cuts (BCTRC)
BCTRC is very meaningful because it represents the predicted portion of the carcass that is salable product. It is calculated using the following formula:  49.936 - (0.0848 x HCW) - (4.376 x BF) - (3.530 x BW) + (2.456 x REA)*. BCTRC ranged from 45.51 to 52.90 and averaged 49.40 ± 1.33%. It was highest for ram lambs (49.75 ± 0.98%) and lowest for wethers 49.04 ± 1.57%). SC were intermediate: 49.48 ± 1.25%

Quality grade
Quality grades indicate the expected eating satisfaction of lamb. There are four USDA quality grades: Prime, Choice, Good, and Utility. Quality grades are determined by three factors: maturity, flank streakings, and conformation. Flank streakings are the fat deposits on the flank muscles. In addition, carcasses must have at least 0.08 inches of BF to qualify for the Choice grade. Eight ram carcasses (38.1%) failed to meet the minimum requirement. Three SC carcasses (16.7%) lacked sufficient BF for the Choice grade. All of the wether carcasses were graded Choice or Prime.

*Source: Scott Greiner, Lamb Carcass Evaluation, Virginia Tech