Characterization of Katahdin Lamb Carcasses in a Traditional Lamb Marketing Context

Abstract The Katahdin breed has grown in popularity in the US, but it is relatively unknown if their carcasses conform to expectations of the traditional commodity lamb industry. Purebred Katahdin wethers (n = 223) were sourced from the genetic reference flock at the U.S. Meat Animal Research Center over two consecutive years. The flock is enrolled in the National Sheep Improvement Program (NSIP) and estimated breeding values (EBV) were available on standard production traits. Lambs were assigned to one of three groups per year based on body weight (BW) and fed a common finishing diet through harvest at similar end BW (51.3 ± 5.6 kg) but varying age (223.8 ± 32.2 d). Lambs were harvested at a commercial processor, hot carcass weight (HCW) was recorded, dressing percentage (DP) was calculated, and carcasses were chilled for 24 h. Carcasses were then ribbed and 12th rib backfat thickness (BFT), and loin muscle area (LMA) were measured. Traits were analyzed in mixed models with fixed class effects of finishing group (6 levels) and rearing type (single or multiple), a linear covariate of harvest age, and a random effect of sire (n = 16). There were no differences in BW, HCW, BFT, and LMA between rearing types but lambs reared as multiples had greater DP than those reared as singles (P = 0.02; Table). End BW increased while DP decreased with lamb harvest age (P ≤ 0.03). Pearson correlation coefficients were estimated between traits including post-weaning weight (PWWT) NSIP EBV. There was a strong, positive correlation between HCW and BFT (0.52) and HCW and BWT (0.54; P < 0.001). In contrast, HCW was only moderately correlated to LMA (0.35; P < 0.001). The PWWT EBV is the best genetic predictor of post-weaning lamb growth and was moderately correlated with end BW (0.38), HCW (0.35), and LMA (0.35; P < 0.001). Traditional markets prefer carcasses to be 29.5 – 36.3 kg HCW and < 6.4 mm BFT; 91% and 51% of Katahdin carcasses were below the HCW and BFT thresholds, respectively. Katahdins are capable of producing lean carcasses that conform to packer ideals for BF when fed to harvest BW of the present study, which may reduce excess fat trimming during fabrication. However, HCW observed in the present study may suggest greater suitability for non-traditional (i.e., ethnic) markets. Lower correlations between carcass traits in Katahdin compared with past research in Western white-faced lambs may highlight important biological differences in growth and fat deposition among divergent breed types. Crossbreeding Katahdin ewes with terminal sire breeds and within breed selection will improve growth and carcass traits without exceeding HCW thresholds commonly reached in wool sheep but should be considered in tandem with other breeding objectives.