Relative Effectiveness of Zeranol (Ralgro^® Magnum implants) with Trenbolone Acetate (Finaplix^®-S) in Yearling Steers

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 is limited.

Objective

To determine the effectiveness of Ralgro Magnum implants administered in conjunction with Finaplix-s for promoting growth in yearling steers on feed approximately 100 days relative to Revalor^®-S.

Materials and Methods

Black and black/white-faced yearling steers purchased from a Nebraska auction were used in this study. The study was conducted at the South Dakota State University research feedlot in Brookings, SD. The steers (280 head; initial weight 864 lb) were randomly allotted to 28 pens. Each pen was assigned to one of four implant treatments, resulting in 7 pens per treatment, 10 head per pen. The treatments were 1) no implant, 2) Revalor-S, 3) Synovex^® Plus and 4) Ralgro Magnum implants + Finaplix-S. Due to problems associated with the implanting of Synovex Plus, the data from treatment 3 were compromised and will not be discussed. The implants were administered once at the beginning of the study.

The steers were fed a 90% concentrate finishing diet averaging 13.4% crude protein and comprised mainly of whole shelled and high moisture corn. Initial weights were unshrunk. A 4% pencil shrink was applied to the final weights. The steers were shipped to a commercial packing plant in Minnesota after 104 days on feed. Carcass data was collected by South Dakota State University and USDA personnel.

Results

Feedlot performance and carcass data are presented in Tables 1 and 2, respectively. Implanting increased steer weight gain 26% and reduced feed required per pound of gain 18%. This translates into 92 additional pounds of weight per steer at market time for only 121 additional pounds of feed. Performance of the steers receiving Ralgro Magnum + Finaplix-S did not differ from that of the steers receiving Revalor-S.

Table 1. Feedlot performance data.

^ab P<.001

^cd P<.05

^e All comparisons of Ralgro Magnum+Finaplix-S vs. Revalor-S P>.40

^f Dry matter.

Implanting increased carcass weight and ribeye area by 54 lb. and .49 in.², respectively and reduced marbling score. Dressing percent, internal fat, fat thickness and yield grade were not affected. There were no differences between Ralgro Magnum + Finaplix-S and Revalor-S for any of these carcass characteristics. Although the proportion of carcasses grading Choice and above was reduced by implanting, overall quality grade tended to be better for Ralgro Magnum + Finaplix-S than Revalor-S. This was the result not only of more carcasses grading Choice but also of fewer carcasses grading Standard.

Table 2. Carcass characteristics

^a 4.00=Slight 0, 5.00=Small 0.

^bc P<.001

^de P<.05.

^f Chi square Ralgro Magnum+Finaplix-S vs. Revalor-S P=.09.

Conclusions

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.