PSVII-19 Serial ultrasound measures of implanted and non-implanted feedlot steers to determine carcass endpoints

Abstract

Abstract An Aloka SSD-500V real-time ultrasound unit, equipped with a 17.2cm carcass probe, was used to serially scan feedlot steers (n = 80; initial BW 271 ± 99) at 42-d intervals during a 378-d feeding period by a certified Ultrasound Guidelines Council (UGC) technician. This included 10 separate ultrasound scanning sessions following the initial weight and ultrasound data taken on day minus 7 (one week prior to initial start date). Steers were randomly assigned to implant treatment (REV) or not (CON) at day -7 with the implanted group being re-implanted on day 190. Cattle were weighed and scanned for 12th-rib fat thickness (FTU), 12th-rib longissimus muscle area (LMAU), percentage intramuscular fat (%FATU), and rump fat thickness (RFU) to determine the ability of ultrasound to predict carcass grading outcomes at harvest in implanted vs non-implanted steers. Eight steers were harvested each 42 days and evaluated 48h after harvest to determine final body weight (FBW), 12th-rib fat thickness (FTC), 12th-rib longissimus muscle area (LMAC), and marbling score (MARB). Data were analyzed to determine treatment (TRT) and days on feed (DOF) interactions using the GLIMMIX procedure. Least square (LS) means illustrated differences (P < 0.05) between TRT for FBW, FTU, REAU, and %FATU. No differences (P = 0.088) between TRT for RFU were observed. Differences (P < 0.05) between DOF were observed for FBW through all 10 weigh days. A difference (P < 0.05) across DOF for days 42, 84, 126, 168, 210, 252, and 294 was noted for FTU. These data suggest growth promoting implants cause differences (increases) in weight and traditional ultrasound measures of carcass endpoints.