Effects of growth-implant regimen on performance, carcass outcomes, activity, and rumination of finishing steers fed to different days on feed

Objective

This experiment evaluated effects of a single extended-release implant compared with 2 re-implant pro- grams administered at either 120 d on feed (DOF) or 80 d before slaughter on growth performance, carcass char- acteristics, activity, and rumination time of feedlot steers slaughtered at 166, 180, 194, or 208 DOF.

Materials and Methods

Using a randomized com- plete block design, steers (n = 6,840; initial BW = 370 ± 7.74 kg) were randomly assigned to 108 pens across 12 treatments in a 3 × 4 factorial arrangement. Treatments were a single extended-release growth implant adminis- tered on d 0 (IMP), an extended-release growth implant administered on d 0 followed by a second implant at 120 DOF (REIMP+120), or an extended-release growth im- plant administered on d 0 followed by a second implant administered 80 d before slaughter (REIMP-80); steers were slaughtered at 166, 180, 194, or 208 DOF. Three-axis accelerometer ear tags were applied to a random subset of steers (n = 1,080) to quantify rumination and activity minutes.

Results and Discussion

Dry matter intake was re- duced, which improved G:F for steers administered RE- IMP+120 and REIMP-80 compared with IMP. Re-im- planted steers tended to have heavier hot carcass weight (HCW) and had greater DP and LM area but less 12th- rib s.c. fat and marbling and lower YG. Choice carcasses were less frequent and Select carcasses were more frequent for re-implanted cattle than for IMP cattle. Final BW increased, concomitant with diminishing ADG and G:F as DOF increased. As DOF increased, there was an increase in HCW, the percentage of carcasses >477 kg, 12th-rib s.c. fat, marbling, YG, and DP. There were greater Choice and fewer Select carcasses with increased DOF. The propor- tion of steers exhibiting buller-steer syndrome was great- est for REIMP-80, intermediate for REIMP+120, and least for IMP. An implant × day interaction for activity minutes indicated that re-implanted steers had increased activity following re-implant.

Implications and Applications

Administration of a second growth implant that overlapped the 200-d ef- ficacy window of an extended-release implant improved G:F, HCW, and DP but decreased carcass fatness and reduced QG regardless of the timing of secondary implant administration.