Carcass Measurements

After determining ending weights (LW) on August 13, the lambs (n=60) were transported to Hamzah Slaughterhouse (in Williamsport, Maryland) for immediate slaughter. The slaughterhouse was 9.5 miles away.

Carcass data was obtained from 51 lambs:  16 ram lambs, 15 short-scrotum lambs, and 20 wethers. Hot carcass weights (HCW) were determined immediately after slaughter. After overnight chilling, the carcasses were evaluated. The carcasses were split between the 12 and 13th ribs to expose the rib eye. A plastic grid was used to measure the area of the rib eye muscle (REA; 20 dots=1 in²). A metal ruler was used measure to backfat thickness (BF) and thickness of the body wall (BWT). Kidney and heart fat (KH) and leg conformation scores (LC) were subjectively evaluated.

Dressing percentage (DP) was determined using the following formula HCW ÷ LW. A few cold carcass weights were obtained. Shrinkage was less than 1 percent. REA was converted to an equivalent weight basis (100 pounds; CWT) using the following formula:  (REA ÷ LW) x 100. Yield grade (YG) was calculated using the following formula:  (back fat x 10) + 0.4. Percent boneless, close trimmed retail cuts (BCTRC) was calculated using the following formula:  49.936 - (0.0848 x HCW) - (4.376 x BF) - (3.530 x BW) + (2.456 x REA)*.

Group	No.	LW	HCW	DP	BF	BWT	REA	CWT	KH	LC	YG	BCTRC
Ram	16	117.5	56.3	48.7	0.122	0.619	3.06	2.66	1.84	12.4	1.62	50.0
Short-scrotum	15	116.5	57.3	49.1	0.113	0.647	3.19	2.74	1.79	12.1	1.53	50.1
Wether	20	104.4	53.4	49.6	0.145	0.640	2.91	2.71	1.85	12.1	1.85	49.7
ALL	51	113.3	55.4	49.2	0.128	0.636	3.04	2.70	1.85	12.2	1.68	49.9

It is not known if any of the differences are statistically significant.

HCW ranged from 37.0 to 72.0 pounds and averaged 55.4 ± 7.5 lbs. The short-scrotum lambs had the heaviest HCW:  57.3 ± 5.3 lbs. HCW of the ram lambs (56.3 ± 8.8 lbs) was more than the wether lambs (53.4 ± 7.6 lbs). DP ranged from 44.9 to 53.3 and averaged 49.2 ± 1.9 percent. The median DP was 49.2 percent. The wethers had slighter higher DP (49.6 ± 2%) than the short-scrotum (49.1 ± 1.7%) and ram lambs (48.7 ± 1.9%).

Jeff Semler

BF ranged from 0.5 to 0.25 inches and averaged 0.128 ± 0.05 inches. The median BF was 0.10 inches. The wether lambs had the most backfat (0.145 ± .056 in) . The short-scrotum lambs had the least (0.113 ± 0.035 in). The ram lambs were intermediate (0.122 ± 0.045 in). BWT ranged from 0.30 to 0.80 and averaged 0.635 ± 0.144 inches. The median BWT was 0.60 inches. The ram lambs had the lowest BWT:  0.619 ± 0.167 inches. Short-scrotum and wether lambs were similar.

REA ranged from 2.25 to 3.85 in² and averaged 3.04 ± 0.45 in². The median REA was 3.10 in². The short-scrotum lambs had the largest REA: 3.19 ± 0.45 in². The wethers had the smallest REA:  2.91 ± 0.48 in². The ram lambs were intermediate: 3.06 ± 0.44 in². REA per 100 lbs. (CWT) ranged from 2.00 to 3.41 in² and averaged 2.70 ± 0.29 in².  The median was 2.64 in². CWT was lowest for the ram lambs (2.66 ± 0.20 in²) and similar for the short-scrotum (2.74 ± 0.32 in²) and wether lambs (2.71 ± 0.32 in²).

KH ranged from 1 to 3 and averaged 1.85 ± 0.65 percent. The median KH was 2.0 The three groups of lambs had similar KH. LC ranged from 10 (low Choice) to 14 (average Prime) and averaged 12.2 ± 0.9. The median LC was 12 (Choice plus). YG ranged from 0.9 to 2.4 and averaged 1.68 ± 0.48. The median YG was 1.40, The short-scrotum lambs had the lowest YG: 1.53 ± 0.35. The wether lambs had the highest YG: 1.85 ± 0.56. The ram lambs were intermediate: 1.62 ± 0.45.

Group	No.	YG 1	YG 2	YG3	≥ Choice	< Choice
Ram	16	11	5	0	14	2
Short-scrotum	15	11	4	0	15	0
Wether	20	8	11	1	18	2
ALL	51	30	20	1	47	4

Thirty lambs (58.8%) were yield grade 1. Only 21 (41.1%) of the lambs were yield grade 2 or 3. Yield grade 1 lambs may be suitable for some ethnic markets, but they are generally considered to be too thin (not finished). They typically sell for lower prices than yield grade 2 or 3 lambs, unless they are sold as feeder lambs for further feeding/finishing.  Four lambs (two rams and two wethers) had less than 0.8 inches of back fat; thus, failing to qualify for the USDA Choice grade. All other lambs graded USDA Choice or higher.

Percent BCTRC ranged from 46.9 to 52.8 percent and averaged 49.9 ± 0.84 percent. There were numerical differences between the three groups, but they are not likely statistically significant. 

Compared to ultrasound data
 While the carcass measurements showed the lambs to have more BF and larger REA, the comparisons between the three groups of lambs were similar, regardless of data source.

Group	No.	BF-scan	BF-carcass	REA-scan	REA-carcass
Ram	16	0.860	0.122	1.81	3.06
Short-scrotum	15	0.900	0.113	1.86	3.19
Wether	19	0.104	0.142	1.69	2.87
ALL	50	0.940	0.127	1.78	3.03

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