Performance and Carcass Characteristics of Feedlot Steers: Effects of Delayed Implanting and Programmed Feeding During the Growing Period1

Professional Animal Scientist, Apr 2004 by Scaglia, G, Greene, L W, McCollum, F T III, Cole, N A, Montgomery, T H

Implanted steers program-fed for a slow rate of gain during the growing period had 91% of the carcasses grading Prime and Choice (Table 4) followed by non-implanted steers program-fed to gain slowly, and non-implanted steers program-fed to gain faster with 71 and 67%, respectively. Implanted steers fed for a faster rate of gain during the growing period had the least proportion (50.0%) of carcasses grading USDA Prime or Choice. Kerth et al. (1995) evaluated the effect of implanting with Ralgro�; Schering-Plough Animal Health, Union, NJ) or Revalor-S� on d 0 (the second implant was Revalor-S� on d 90 of the feeding period for all cattle) on characteristics of 1574 beef carcasses from Continental European, Continental European � British, and British-type cattle. Source of implant did not affect marbling score; USDA quality grades; adjusted preliminary yield grade; percentage of kidney, pelvic, and heart fat; and carcass weight for Revalor-S�/Revalor-S� or Ralgro�/Revalor-S�, respectively. However, a larger Longissimus area and lesser USDA Yield Grade was reported for cattle implanted twice with Revalor-S�.

The correlation coefficients of ultrasound measurements of fat thickness and marbling score at the beginning and at re-implantation during the finishing period with yield grade, quality grade, fat thickness, and marbling score are presented in Table 5. Ultrasound measurements of fat thickness at the beginning (d 1) and at re-implantation during the finishing period (d 67) were correlated to actual fat thickness (P

The regressions predicting external fat and marbling score at two different times in the experiment are given in Figure 1. Again, the closer the ultrasound measurement was conducted to the day of harvest, the greater the correlation of final fat thickness and marbling score. The r^sup 2^ for fat thickness altered from 0.261 on d 1 to 0.545 60 d before harvest. A similar tendency was observed for marbling score, with an r^sup 2^ that altered from 0.277 on d 1 to 0.431 60 d before harvest. At the beginning of the feeding period, ultrasound technology was not an accurate predictor of external fat endpoint for steers with an average age of 8 mo because they did not have enough external fat deposits (

Implications

Overall, results of this experiment indicate that programmed feeding during the growing period did not affect feed intake and ADG during the finishing period. Delaying the first implant until the beginning of the feedlot phase and programmed feeding during the growing period are tools that may be used to increase BW gain efficiency of beef steers during the feedlot phase and have a positive contribution on cost of gain in a finishing program. Measurement of fat thickness using ultrasound technology to estimate time of harvest may be a useful tool to decrease time on feed.

1 This research was funded by the Texas Agricultural Experiment Station and the Beef Carcass Research Center, West Texas A & M University. Reference to a company or trade name does not imply endorsement or approval by the Texas Agricultural Experiment Station, West Texas A & M University, or USDA-ARS.