The Use of Ultrasound Technology for the Prediction of Marbling or Days on Feed and the Effect of Implants on Marbling in Incoming Feedlot Steers

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