Zeranol with Trenbolone Acetate in a Re-implant Program For Yearling Steers: Optimum Timing and Relative Effectiveness

Introduction

It is well documented that estradiol (E₂) and trenbolone acetate (TBA) administered together improve gain and efficiency of feedlot steers more than either anabolic compound administered by itself. As a result, it has become a common practice in feedlots to use implants containing both. However, reduced quality grade has been a persistent problem associated with the use of these implants. Because of declining beef demand, quality and consumer acceptance have become major issues for the beef industry.

Previous work has suggested that administration of zeranol and TBA results in feedlot performance improvements comparable to those of E₂ and TBA but better quality grade. However, data addressing this question are limited. Moreover, the question of timing of zeranol and TBA following an initial Ralgro^® implant has not been addressed.

Objectives

To determine 1) optimum timing of Ralgro Magnum implant + Finaplix-s administration following an initial Ralgro implant and 2) effectiveness of Ralgro/Ralgro Magnum + Finaplix-S relative to Ralgro/Revalor^®-S in yearling steers on feed approximately 150 days.

Materials and Methods

British and Continental crossbred steers from Kansas, Oklahoma and Texas were used in this study. The study was conducted at a commercial research feedlot in the Texas Panhandle. The steers (1988 head; initial weight 720 lb) were randomly allotted to 20 pens. Each pen was assigned to one of five implant treatments (Table 1) resulting in 4 pens per treatment, 89 to 111 head per pen.

Table 1. Implant treatments.

The steers were fed an 89% concentrate finishing diet averaging 14.5% crude protein and comprised mainly of flaked corn, high moisture corn and flaked wheat. Initial weights were unshrunk. A 4% pencil shrink was applied to the final weights. The steers were shipped to a local packer after 154 days on feed. Carcass data were collected by Cattlemen’s Carcass Data Service, West Texas A & M University, Canyon, Texas.

Results

Feedlot performance data are presented in Table 2, and carcass characteristics are presented in Table 3.

Table 2. Feedlot performance data (deads and rejects in).

^a Dry matter.

^b P=.01

^c P=.02 for contrast MF0 vs. Ral/MF50, Ral/MF70 and Ral/MF90.

^d P=.06

^e P=.10 for contrast Ral/Rev70 vs. Ral/MF70.

f P=.01

^g P=.02, h P=.06

ⁱ P=.08 for contrast Ral/MF50, Ral/MF70 and Ral/MF90 quadratic effect.

Table 3. Carcass characteristics.

^a P=.02

^b P=.04

^c P=.05

^d P=.06

^e P=.07

^f P=.09

^g P=.10 for contrast MF0 vs. Ral/MF50, Ral/MF70 and Ral/MF90.

^h P=.02 Ral/MF50, Ral/MF70 and Ral/MF90 quadratic effect.

ⁱ P=.03

^j P=.07

^k P=.08 for contrast Ral/Rev70 vs. Ral/MF70.

^j 3.00=slight 0, 4.00=small 0, etc.

Ral/MF50, Ral/MF70 and Ral/MF90 steers grew faster and more efficiently than MF0 steers. The length of this trial (154 days) appears to have exceeded the effective lives of the Ralgro Magnum implants and Finaplix-s implants. However, the MF0 treatment resulted in more steers grading Choice or better and fewer steers grading Select or Standard than any other treatment.

Ral/MF70 steers gained faster and tended to be more efficient than the RalRev70 steers as well as those receiving the other Ralgro Magnum + Finaplix-s treatments.

Dressing percent was less for Ral/MF70 than the other treatments. As a result, hot carcass weights of the Ral/MF70 steers were not different from those of Ral/Rev70 or the other Ralgro Magnum + Finaplix-S treatments.

Not only did the Ral/MF70 treatment result in percent Prime + Choice similar to that of Ral/Rev70, it also reduced the percent Standard by 40%. In fact, the Ralgro Magnum + Finaplix-s treatments on the whole reduced Standards by about half. In other words, the use of Ralgro Magnum implants and Finaplix-S improved overall quality grade relative to Revalor-S by moving cattle up from Standard into the Select grade.

Conclusions

1) Ralgro Magnum + Finaplix-s was at least as effective at increasing growth rate and efficiency of yearling steers as Revalor-S when following an initial Ralgro implant.

2) Optimum re-implant timing of Ralgro Magnum + Finaplix-S for feedlot performance was 70 days after the initial Ralgro implant. Reimplanting at 70 or 90 days tended to be more effective than 50 days when evaluated on a carcass basis.

3) Compared to Revalor-S, Ralgro Magnum + Finaplix-S improved overall quality grade by reducing the proportion of cattle grading Standard or lower.

4) Reducing time until slaughter from 104 to 64 days after implanting with Ralgro Magnum and Finaplix-s did not negatively affect quality grade.

Ralgro is a registered trademark and Magnum is a trademark of Schering-Plough Animal Health Corporation.

Revalor-S is a registered trademark of Hoechst Roussel Vet.

Finaplix is a registered trademark of Elanco.