Performance Narrative:

Activities Performed:

Two University of Idaho (UI) Sheep Center breeding groups included Targhee/Polypay ewes with a Suffolk ram and Targhee/Polypay ewes with a Dorper ram. Wool lambs (n = 9) and composite lambs (n = 9) were born at the UI Sheep Center, and purchased by the research project at an average age of 69 days. The hair (Dorper) lambs (n = 9) were purchased from a local producer at an average age of 79 days. The purchased hair lambs entered a 30-day quarantine at the UI Sheep Center upon arrival. Once the trial began, all lambs were raised on the University of Idaho TMR, formulated by a university nutritionist. Feed was weighed out each feeding at (07:00 and 15:00), amount fed varied depending on prior feedings. Following quarantine, the hair lambs were integrated into the same pen as the original lamb groups. They were raised in the same environment until harvest on three separate dates, 9/13/2021, 10/04/2021, and 10/18/2021. Growth measurements, weight (lbs.), heart girth circumference (in), and shoulder height (in) were taken at (08:00) on Day 0 and the two final days averaged prior to each harvest to calculate for average daily gain (Table 1).

Feed samples were taken weekly from the main feed pile, placed into 1 lb. gallon freezer Ziploc bags and frozen in a -20C freezer. Samples were then mixed, 1/4th of each week into a composite feed sample of the 4 samples taken throughout the month. Five samples, one composite sample for each month, were shipped on March 28th to Dairy One, Forage Lab in 0.5 lb. samples for analysis.

Lambs were harvested under USDA Inspection at the UI Meat lab when they reached ~0.2 in of 12th rib fat thickness as estimated by trained University of Idaho personnel. Three groups of nine lambs were harvested with 3 lambs from each treatment in the first two harvests. The final harvest date contained two treatments of two lambs due to pulling two lambs for health reasons during the feeding period. Directly after harvest, the lambs hot carcass weights were recorded before being placed in the cooler for 48 hours. At 48 hours postmortem lambs were ribbed and each lambs back fat, back wall, rib eye area, % boneless closely trimmed retail cuts, conformation, flank streaking, quality grade, and yield grade were measured following USDA guidelines (USDA, 1992). Hot carcass weight, back fat, and rib eye area means are shown (Table 2). Carcasses were fabricated, and the lamb loin (IMPS 231, NAMP 2014) was removed and weighed. They were then vacuum sealed with bone guard and aged at 0C until 10-d post-harvest. Loins were weighed after removal from the vacuum seal bags to determine storage loss.

Following the 10-d aging period, 1-in bone in loin chops were cut utilizing a bandsaw and assigned to thiobarbituric reactive substance (TBARS), retail display, Warner-Bratzler shear force, sensory, Fatty Acid Methyl Esters (FAMES), and volatile compounds. The retail and TBARS chops were placed in Styrofoam trays and overwrapped with an oxygen permeable PVC film. The additional chops were sorted into their various analysis groupings, vacuum sealed, and frozen at -20 C until analyses were conducted.

Retail display chops were displayed in a glass retail display case at 2-4C for 4 days. The chops were allowed to bloom for 60 minutes, before oxygenated lean color (1 = extremely bright cherry-red, 8 = extremely dark red), surface discoloration (1 = no discoloration 0%, 6 = extensive discoloration 81-100%), amount of browning (1=No evidence of browning, 6= Dark brown), discoloration (1 = none, 5 = extreme), color uniformity (1 = uniform no two-toning, 5 = extreme two-toning), and bone marrow color (1 = bright reddish-pink to red, 7 = black discoloration) were measured by three evaluators on day 0,1,2,3, and 4 at (08:00) following American Meat Science Association Guidelines (AMSA, 2012). To avoid effects due to display case location, chops were rotated after each measurement. Subjective color measurements for each treatment are shown (Table 3). To analyze instrumental color, chops bloomed for at least 60 minutes before 2 objective color measurements were taken for lean and marrow. Measurements were taken once daily using a Nix color sensor, on day 0 of retail display with subsequent measurements taken on days 1, 2, 3 and 4 at (08:00). The instrument was set to illuminant D65 and Commission International del Eclairage (CIE) L*(lightness), a* (redness), and b* (yellowness) values were recorded. Objective color measurements for each treatment are shown (Table 4).

Thiobarbituric acid reactive substances (TBARS) an indicator of lipid oxidation was analyzed on days 0 and 4 of retail display following the protocol in Section XI, Appendix O of the Meat Color Measurement Guidelines (AMSA, 2012) with the following adjustment of using 0.25g samples in duplicate. Samples were excised from the longissimus dorsi, avoiding large pieces of fat, connective tissue and the exposed edges of the chop. Lipid oxidation measurements are recorded for each treatment (Table 5).

Chops were cooked to an approximate internal temperature of 160F using clamshell Cuisinart grills with one chop per treatment on each grill. The internal temperatures were continually monitored during grilling using probes inserted into each chop.

After cooking as described above, the chops rested before being sliced into three equal portions and placed into covered labeled cups. These cups were kept warm prior to being served to a panelist who received one cup from each treatment. The consumer panel (n=81 panelists) rated samples for overall acceptability, texture, juiciness, and flavor using a 10-point scale where (10=like extremely and 1=dislike extremely). Consumer sensory analysis responses are recorded (Table 6). Consumers were asked if they could detect an off flavor, if they would purchase the product and what trait (flavor, juiciness, or tenderness) they liked the most and least. Consumer responses are recorded in percentages (Table 7).

Two chops from each lamb were used for WBSF. Chops were weighed prior to and after cooking to calculate cook loss. Peak temperature of each chop was recorded. Chops were cooked as described above then cooled to room temperature, once cool each chop had three 1.27-cm removed parallel to the muscle fiber direction cores following the guidelines of Section VIII, Appendix B (AMSA, 2015). Cores were then sheared perpendicular to the muscle fiber direction using a WBSF machine. The force required to shear through the chops core is representative to the force needed to chew each chop (Table 8).

Volatile compound analysis was performed at Texas Tech University using Gardner and Legako methods (2018). Sample preparation occurred at University of Idaho. To prepare the samples the chops were cooked as described above, cubed and placed into liquid nitrogen. Frozen cubes were homogenized, placed into labeled bags and stored at -80C until temperature-controlled shipment to Texas Tech University for analysis (Table 9).

The protocol described by O'Fallon et al. (2007) will determine fatty acid concentration of chops. Frozen, raw chops were liquid nitrogen homogenized and placed into labeled bags and shipped to Texas Tech University where further analysis was performed (Table 10).