Evaluation of Growth Promoting Implant Strategies and Days on Feed on Finishing Heifer Performance and Evaluation of Optimal Reimplant Times for Finishing Heifers and Steers

Authors

• Caitlin .. Ohnoutka, University of Nebraska-LincolnFollow

First Advisor

Galen E. Erickson

Date of this Version

Summer 8-2018

Document Type

Thesis

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In partial Fulfillment of Requirements For the Degree of Master of Science, Major: Animal Science, Under the Supervision of Professor Galen E. Erickson. Lincoln, Nebraska: August 2018

Copyright © 2018 Caitlin A. Ohnoutka

Abstract

Two experiments evaluated the effects of delayed, long-acting coated implants or uncoated implants to non-implanted heifers fed for constant or varying days on feed. In Exp. 1, heifers were implanted with either Revalor-XH on d 1, Revalor-200 on d 1, Revalor-XR on d 1, or Revalor-200 on d 70 compared to non-implanted control heifers when fed for an average of 198 d. In Exp. 2, heifers were implanted with Revalor-200 on d 1 and reimplanted with Revalor-200 on d 100, Revalor-XH on d 1, or not implanted and fed for different days on feed: 151, 165, 179, or 193. Implanting heifers increased BW, ADG, G:F and HCW compared to non-implanted heifers with no differences between implant strategies. As heifers were fed for longer DOF, ADG and G:F decreased. Implanting and increasing DOF substantially increased BW and HCW but increasing initial implant dosage did not result in a performance advantage when heifers were fed for varying DOF.

Two experiments evaluated the effect of timing of administering a terminal implant in heifers and steers when fed for 180 days. In Exp. 3, heifers were implanted with Revalor-IH and reimplanted with Revalor-200 at 20, 60, 100 or 140 DOF. In Exp. 4, steers were implanted with Revalor-IS and reimplanted with Revalor-200 on 20, 60, 80, 100 or 140 DOF. In Exp. 3, final BW, ADG, G:F, HCW and LM area responded quadratically and were maximized between 88 and 103 on terminal (DOT) implant. In Exp. 4, carcass-adjusted final BW, ADG, G:F and HCW responded quadratically and was optimized between 87 and 104 DOT. Therefore, the optimal duration for a terminal implant appears to be between 80 and 120 DOT, with an average of 96 DOT for both heifers and steers.

Advisor: Galen E. Erickson