Effects of harvest season on carcass characteristics of lambs in the Intermountain West

Authors: WHALEY, JAELYN - South Dakota State University; Murphy, Thomas - Tom; GIFFORD, CODY - University Of Wyoming; MEANS, WARRIE - University Of Wyoming; RITTEN, JOHN - University Of Wyoming; MCKIBBEN, HEATHER - University Of Wyoming; PAGE, CHAD - Utah State University; STEWART, WHITNEY - University Of Wyoming

Submitted to: Applied Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2022
Publication Date: 10/31/2022
Citation: Whaley, J.R., Murphy, T.W., Gifford, C.L., Means, W.J., Ritten, J.P., McKibben, H.N., Page, C.M., Stewart, W.C. 2022. Effects of harvest season on carcass characteristics of lambs in the Intermountain West. Applied Animal Science. 38(5):393-401. https://doi.org/10.15232/aas.2022-02322.
DOI: https://doi.org/10.15232/aas.2022-02322

Interpretive Summary: Despite historical decreases since the 1970’s, recent trends suggest lamb consumption in the U.S. has increased 56% from 2011 to 2020. Nevertheless, the U.S. imported 63% of its lamb supply in 2020 with 98% of total lamb imports from Australia and New Zealand. Therefore, improving the quality and preference of domestically produced lamb is at the forefront of U.S. sheep industry efforts. An in-depth lamb carcass survey has not been conducted in the U.S. since the 1980’s, let alone in the Intermountain West where a large proportion of U.S. lamb is produced. The objectives of this study were to characterize seasonal differences and interrelationships of lamb carcass characteristics at two large commercial processing plants located in the U.S. Intermountain West. Over 10,000 lamb carcasses were surveyed for economically important quality indicators from May 2018 to May 2019. Carcasses of lambs harvested in the spring were 3.4 kg heavier than those harvested in the summer. Commercial yield grade and fat thickness also tended to be greater in the spring than summer. Overall, lamb carcasses exceeded the abattoir's preferred weight by 5% and industry acceptable fat thickness by 25%. Results indicate U.S. lamb is excessively fat and substantial improvement in quality is warranted to remain competitive with domestic and international red meat products. This issue does not appear to be attributable to a single sector of the U.S. lamb industry but is an inherent challenge due to the seasonality of sheep production systems. Transparent dialogue across industry segments (seedstock, ewe-lamb, lamb feeder, abattoir) should be prioritized, in addition to consistent integration of value-based pricing to reduce the proportion of overly fattened lambs.

Technical Abstract: Objective: The objectives of this study were to survey characteristics including hot carcass weight (HCW), 12th rib fat thickness (RFT), body-wall thickness (BWT), longissimus muscle area (LMA), USDA yield grade (USDA YG), percentage closely trimmed retail cuts (RC), andcalculated yield grade (Calc YG) of lamb carcasses in the Intermountain West to determine the effects of season of slaughter and interrelationships among carcass characteristics. Materials and Methods: Lamb carcass characteristics were evaluated in two commercial Intermountain West processing plants over one year (n = 10,027). Carcasses were evaluated by season: spring (December – April, n = 2,322) and summer (May – August, n = 7,705). Results and Discussion: Carcasses of lambs harvested in the spring had 3.4 kg heavier HCW (P = 0.04) than those harvested in the summer. Commercial yield grade (YGUSDA) was also greater in the spring (P < 0.001). Subcutaneous fat (RFT; P = 0.06) and YGCalc (P = 0.09) tended to be greater in the spring than summer. Correlation coefficients as well as models of fit with a linear covariate of HCW indicated negative relationship between HCW and RC and positive relationship with all other carcass traits (P < 0.001). Overall, graded lamb carcasses exceeded commercial processing plant preferred HCW (38.6 kg) by 5% (mean = 40.5 kg) and industry acceptable RFT (6 mm) by 25% (mean = 8.03 mm). Furthermore, 70% of lamb carcasses exceed 6 mm RFT. Implications and Applications: Season of slaughter contributed to differences in HCW and USDA YG but no other carcass characteristics. Still, carcass data surveyed from the largest lamb-producing region of the United States suggests that the degree of fatness exceeds industry preferences. Although abattoirs mitigate adverse effects of excessive fat through trimming and diverse market outlets, industry-wide efforts that agree on acceptable standards of trimness are needed. Transparent dialog across industry segments should be prioritized in addition to consistent integration of value-based pricing to reduce the proportion of excessively finished lambs.