Comparison of Three Trenbolone Acetate / Estradiol Implant Programs on the Performance and Carcass Characteristics of Long Fed Heifer Calves in western Canada.

Dr. Janice Berg, Robert Stilborn,
Lakeside Research, Brooks Alberta

and Dr. Grant Royan
Hoescht-Rousell Vet, Regina Saskatchewan

Introduction

Feeding heifers presents a unique challenge. Heifers have a cyclic change in hormone status every 21 days, and feed intake, gain and feed conversion of heifers is less than steers. Implanting feedlot heifers with combination trenbolone acetate/estradiol implants improves feedlot performance compared to implanting with conventional estradiol/testosterone implants. This trial was conducted to compare three implant programs for long fed heifer calves.

Materials and Methods:

Trial Facilities: The trial was conducted in a research feedlot operated in conjunction with a 75,000 head commercial feedlot. The animals were housed in open air, dirt floor pens (6.1 m X 17.1 m) arranged side by side with a front feeding alley.

Experimental Animals: The experimental animals were chosen from 251 good quality recently weaned heifer calves, 6 ­ 8 months of age, purchased by private treaty or from local auction markets. The heifers were crossbred Charolais typical of those fed in western Canada.

Experimental design: The trial was a randomized block design with three treatments per block and 8 replications of each block. There were 24 head in each block. A total of 192 heifers were selected for the trial.

The three experimental groups were:

Group I: 64 heifers were implanted on Day 0 of the trial with Revalor-H and reimplanted on Day 91 with Revalor-H

Group II: 64 heifers were implanted on Day 0 of the trial with Ralgro³ and reimplanted on Day 63 with Revalor- H

Group III: 64 heifers were implanted on Day 0 of the trial with Synovex³­H and reimplanted on Day 91 with Revalor-H

Animal allocation: .All animals were individually weighed on Day -1, Day 0, Day 63, Day 91, Day 154, and the two days immediately prior to the day of slaughter.The on trial weight was the average of the weight on Day -1 and Day 0.The heifers were slaughtered by block based on a visual appraisal for finish.

Feeding and watering:. Feed was delivered to the feed bunks by a truck-mounted mixer on load cells. Monensin (Rumensin) and tylosin (Tylan) were included in the diet at the manufacturer's recommended inclusion rate. Water was available ad libitum from automatic waterers.

Feed formulations: Heifers were fed a grower ration for the first 63 days on feed and then were adapted to a high concentrate diet by increasing the amount of barley in the ration and decreasing the amount of silage over a three week period. The finishing diet was fed for the remainder of the trial. The finishing diet was approximately 80% barley, 15% silage and 5% supplement on a dry matter basis.

Results:

One heifer died from bloat during the study, no heifers were removed. The heifers were slaughtered in three groups at Day 187, Day 213 and Day 226. The final finishing ration averaged 12.4% crude protein and a NEg at 0.613 mcal /lb. Heifers were on feed for an average of 211 days.

Performance:

1. Average Daily Gain:
The heifers had similar body weight gains from Day 0 — Day 63, Day 91 — Day 154, Day 154 —market and Day 0 — market. From Day 63 — Day 91 the heifers implanted with Ralgro Day 0 and reimplanted on Day 63 with Revalor-H gained significantly faster (p < 0.05) than the heifers implanted with Synovex-S on Day 0.

2. Daily Dry Matter Intake:
Heifers implanted with Synovex-H Day 0 consumed less feed than the heifers implanted with Ralgro or Revalor-H during the first weigh period Day 0 — Day 63. There was no difference in dry matter consumption during the remainder of the trial.

3. Feed Conversion:
There was no difference in feed conversion except during the period from Day 91 — Day 154 when the heifers implanted with Synovex H on Day 0 and reimplanted with Revalor-H on Day 91 had a better feed conversion than the heifers implanted with Ralgro at Day 0 (p < 0.05).

Performance Summary:

The performance of the heifers was similar with all three implant programs. The data is summarized in Table 1 on a live weight basis and Table 2 on a carcass adjusted basis.

Table 2: Performance Summary — Carcass Adjusted Basis
Initial Implant	Revalor-H	Ralgro	Synovex H
Re implant	Revalor-H	Revalor-H	Revalor-H
Initial Weight	593.9	594	594.7
Final Weight	1185.9	1181.3	1186.2
Days on Feed	211	211	211
Average Daily Gain	2.81	2.78	2.80
Daily Dry Matter Intake	18.14	18.21	17.50
Feed Efficiency	6.46	6.55	6.25

Carcass adjusted bases = Hot Carcass Weight divided by a common Dressing Percent = 0.605

Discussion:

There was no significant difference in feedlot performance between the three implant programs. Trials with steer calves have generally shown similar results utilizing the same type of implant programs. Carcass results also follow the pattern shown with steer calves, utilizing RALGRO as the initial implant in a reimplant program, with the terminal implant being a Revalor implant, results in a greater number of the carcasses grading AAA. This trial supports the contention that the initial implant has an impact on marbling and subsequent quality grade. There is no economic advantage with a Revalor-H/Revalor-H implant program. A Synovex H/Revalor-H implant program gives the best feedlot performance, a RALGRO/Revalor implant program resulted in significantly more carcasses grading AAA quality grade.

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