Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Animal Science


A 2-year study using three hundred five crossbred yearling steers was conducted to determine if ultrasound technology could be used on incoming feedlot steers to predict final marbling score at slaughter or days on feed to reach 1 cm backfat. Implants were administered at processing to study the effects of anabolic agents on steer marbling score. Steers were vaccinated, weighed, and randomly assigned to implant treatment upon arrival at a commercial feedyard. Treatments were trenbolone acetate + estradiol, estradiol benzoate + progesterone or no implant. Estimates of breed composition, hip height measurements, ultrasound scans for 12th rib fat thickness, rib eye area and percentage of ether extract in the rib eye were obtained at processing. Year 1 data were used to develop a marbling score prediction equation. Year 2 data were used to develop an equation to solve for predicted day on feed to reach 1 cm backfat. Steers were fed in a single pen and slaughtered at a commercial packing plant with carcass data collected after a 24-hour chill. Data were analyzed by correlation and regression techniques. Implants had a significant effect (P<.05) on average daily gain, hot carcass weights, and rib eye areas when compared to controls. Steers implanted with Revalor tended (P<. l 0) to have heavier hot carcass weights than Synovex implanted steers. Implants had no significant effect on 12th rib fat thickness or yield grade. Implants significantly (P<.05) decreased marbling scores when compared to nonimplanted steers. Revalor implanted cattle had significantly lower marbling scores (P<.05) when compared to Synovex cattle. The correlation between marbling score and initial ether extract for year 1 cattle was .45 (P<.0001). The total R2 for the model predicting marbling score was .2791. The equation predicting marbling score was Pred Marbling Score= 3.95 + (.24*BLACK) - (.98*REV) + (.56*EE) + (.44*1NT), where BLACK = 1 if the coat color was black and O if any other color, REV = 1 if implanted with Revalor and O if implanted with Synovex or not implanted, EE = percentage of initial intramuscular fat as determined by ultrasound measurement, and INT = EE X REV interaction. Days on feed was positively correlated with hot carcass weight (P<.001), backfat (P=.05), shrunk weight, and kidney pelvic and heart fat (P<.0001). Correlations were .28, .22, .35, and .66 for hot carcass weight, backfat shrunk weight, and kidney, pelvic, and heart fat, respectively. Actual days on feed, initial backfat, and coat color were used to develop an equation predicting backfat. This backfat equation was then used to algebraically solve for days on feed (DOF) to reach 1 cm backfat. The R2 for this equation was .1 397. The backfat equation was Pred backfat = -.779 + .014*DOF + 1.622*BF1 + .279*BLACK. The equation to solve for days on feed was 127.1 - 115.9*BF1 - 20.0*BLACK here BFI = initial backfat measurement as determined by ultrasound and BLACK= 1 if coat color was black and O if any other color. Both the marbling score and days on feed prediction equations did a very poor job predicting end points. Currently, these equations could not be used to accurately estimate marbling score or days on feed.

Library of Congress Subject Headings

Beef cattle -- Carcasses Beef cattle -- Feeding and feeds Ultrasonic imaging



Number of Pages



South Dakota State University