Technical Reports

A Comparison of Estradiol-Trenbolone Acetate Implant Programs for Yearling Steers of Two Genotypes

Robbi H. Pritchard, Ph.D.
Department of Animal and Range Sciences
South Dakota State University, Brookings

Introduction
Approach
   Table 1. Diets Fed
   Table 2. Processing Schedule
Results
   Table 3. Pooled Performance Summary
   Table 4. Breakout of Interactions between Implant Treatment & Cattle Type
   Table 5. Effect of Implant Treatment on Carcass Traits
   Table 6. Marbling Scores and Choice % by Implant X Cattle Source^ab
Conclusions

Introduction

Optimizing implant strategies requires striking a balance between implant payout, production cost, and carcass value. We realize that the influence of implants on cost of gain erodes over time. We also consider that carcass marbling is improved as the elapsed time from implanting to slaughter is increased (Wagner and Pritchard, 1991). The label associated with implant clearances does not stipulate how days relate to these variables.

The number of available estradiol-trenbolone acetate (E2TBA) implant products is expanding. These are potent tools for feedlot managers to use. In 1996 there were two E2TBA products available (Revalor^®-S and Synovex^® Plus) that varied in the ratio of estradiol: trenbolone acetate. They also differ in the way they are manufactured. We were curious as to the relative effective payout of these two products.

To evaluate effective payout, I think it is advantageous to have a non-implanted control to use as a moving reference point during growth. It would also be advantageous to have a positive control that provides high levels of implant payout during the same time frame associated with the expected depletion of the test implant(s). One way to accomplish this would be to administer implants in a staggered time schedule in the positive control treatment. Coincidentally, this also provides a look at the relative usefulness of a re-implant program.

In the experiment described here we wished to evaluate the relative effective payout for Revalor-S¹ and Synovex Plus.² Non-implanted steers were used as the negative control. The positive control involved delaying Revalor-S implanting for 56 days to provide a staggered payout during the later stages of the feeding period. In the positive control, Ralgro^®3 implants were used to provide early growth-promoting activity.

Approach

The original protocol called for evaluating implant strategy response by steers over a 140- to 150-day feeding period. The implant strategies used included 1) Control (non-implanted); 2) Synovex Plus; 3) Revalor-S; and 4) Ralgro-Revalor-S. The Synovex Plus, Revalor-S and Ralgro implants were administered on day 1. The re-implant with Revalor-S was administered after 56 days on feed.

Forty pens of 10 steers were assigned to the experiment. Steers were purchased as two major groups. Group I consisted primarily of black-hided steers, and Group II was predominantly continental crosses. Each group provided enough steers to fill 20 pens (5 pens per implant treatment/per group). The groups were fed and managed as distinctive lots of cattle to accommodate differences in implant response and marketing needs that could occur between differing biological types. The nutrition, processing and implant management were common across groups.

The 200 steers used in Group I were selected from a group of 223 steers. The Group II steers were drawn from a pool of 234 steers. At arrival cattle were observed for thriftiness, structural soundness and type characteristics. Any unacceptable subjects were deleted. Within a source group, cattle were ranked by arrival body weight (BW), and outliers were deleted. Once the pool was reduced to 200 subjects, treatment was assigned (1 to 4) using a random sequence of treatment codes. Data were resorted by treatment and BW and assigned a random sequence of replicate codes. The treatment-replicate combinations were then assigned pen numbers such that treatment was randomly distributed throughout the 20 pens allocated to the group. This allotment system distributes BW ranges in all pens. Starting dates were May 1, 1996 for Group I and May 23, 1996 for Group II.

Incoming cattle were eartagged and then vaccinated for IBR, BVD, PI3, H. somnus and 7 clostridial species, using Ultrabac 7⁴ and Resvac 4/Somubac.⁴ Parasite control was provided by administering Expar³ (external) and Panacur¹ (internal). During processing, ears were palpated for evidence of viable implants. None were found. During the receiving period, long hay and the step 1 diet (Table 1) were fed. Milled feed delivery was limited to 1.5% BW during receiving.

Table 1. Diets Fed

^aSwitch diets on August 20, 1996.

^b70% DM contained 460 g monensin/T AFB. Diet 28.5 g monensin/T DMB.

cFed as a pelleted supplement that included Tylosin. Diet 11 g Tylosin/T DMB.

Initial and final individual BW were recorded on two consecutive days. Initial implants were administered during the second initial BW process. Re-implanting with Revalor-S was done during the d-56 BW processing. Implant integrity was evaluated at the next weigh day following implanting. Interim BW were determined as noted in Table 2. All BW were collected with no prior restriction of feed or water.

Table 2. Processing Schedule

Cattle were fed twice daily. A five-step program was used to adapt cattle to the feed (Table 1). Feed calls were made at 0700 each morning based on bunk and cattle condition. A clean bunk management system was used. Rations were mixed using a stationary mixer. A single batch was distributed within replicate so that implant treatment and feed batch were not confounded. Samples of feed ingredients were collected once each week. The analysis of these samples was combined with batching records to reconstruct the composition of diets fed. While on step 5, these diets contained: DM 75.5% ± .5; CP 12.4% ± .07; ADF 5.6% ± .15; NDF 12.6% ± .8; ash 2.7% ± .04; NEm 94.8 Mcal/cwt ± .12; and NEg 63.7 Mcal/cwt ± .10. These weekly assays and feed delivery records were used to produce DMI summaries each week or more frequently when necessary.

Initial and interim BW reported in Table 3 were not corrected for fill. The Final BW referred to in Table 3 included a 3% pencil shrink. This shrunk BW was used to calculate cumulative ADG and dressing percentage. To evaluate the performance response to the re-implant program (4), performance variables were summarized for the periods prior to (EARLY) and following re-implanting (LATE). The Group I cattle were fed for 131 days, and the Group II were fed for 145 days. This caused the LATE performance windows to be 57 to 131 and 57 to 145 days, for Group I and II respectively.

Two steers were realized from the study, one for lameness and one as a burnout. Realized steers had been individually hospitalized prior to deleting them from the study. Their BW contribution to the pen mean was deleted from the onset of the experiment. Feed records were corrected for the days the subjects were hospitalized. It was assumed that realizers consumed pen average DMI up to the point of hospitalization.

On the evening following the final BW, steers were transported 75 miles to the beef packing plant at Luverne, Minn. They stood overnight and were processed at 0700 the following day. Individual carcass identity was maintained. Hot carcass weight was recorded the day of slaughter. Cold carcass data, longissimus area, ribfat thickness, marbling score, bone maturity, lean maturity, KPH (omitted in Group I) and masculinity were collected 24 hours after exsanguination. Data were collected by SDSU personnel trained in carcass evaluation.

One steer was mishandled during transit and was not slaughtered as part of this experiment. Consequently, carcass data were available for 397 subjects.

All performance variables were evaluated in a statistical model that included treatment, group, and the treatment x group interaction using the GLM package of SAS. The experimental unit in these analyses was the pen. Orthogonal contrasts were used to separate treatments. The contrasts included: (a) control vs. implants; (b) Synovex Plus and Revalor-S vs. Ralgro/Revalor-S and (c) Synovex Plus vs. Revalor-S. Carcass data were handled similarly except that the individual steer was recognized as the experimental unit.

Results

The initial BW for Groups I & II were 782 lb ± 5.5 and 661 lb ± 4.2, respectively. The predominantly Angus x Hereford steers in Group I were large framed and had never been implanted prior to entering our feedlot. It is unusual that the continental cross steers used in this study were smaller framed than the Angus x Hereford steers. The baldies were of exceptional quality. Initial body condition was not quantified. Flesh was considered comparable between the groups and typical for yearlings entering our feedlot. Feeding conditions were excellent throughout the duration of this trial, and cattle performance reflects these conditions.

Implants increased (P<.001) ADG and DMI and reduced (P<.001) feed/gain at closeout. These responses were evident during most interim measures of performance (Table 3). In the latter stages of the feeding period, interactions developed between cattle group and implant treatment for ADG and feed/gain. The non-implanted steers in Group II were growing more rapidly and more efficiently than Group I steers during 113 to 130 days on feed. These (Group II) steers started on feed at a lighter weight and were not as close to finish at 130 days. In contrast, the Group II steers implanted with Synovex Plus had lower ADG at 112 days (3.63 v 3.09) and 130 days (3.47 v 2.44) than Group I contemporaries. The DMI of these steers also tended to be lower during these interim periods.

Table 3. Pooled Performance Summary

^aP>.15.

^bFinal BW includes a 3% shrink.

Short intervals between BW measurements can be misleading. To average responses over time, ADG from 90 to 130 days was calculated (Table 3). These means clearly show that cattle were becoming less efficient as they approached slaughter BW. A response to implanting was still in effect, as feed/gain was 15% lower in steers receiving Synovex Plus or Revalor-S on d-1 than in non-implanted steers. There was an additional 11% improvement (P<.01) in feed/gain of re-implanted steers during this period.

To evaluate the merits of re-implanting, data were calculated for 1 to 56 (EARLY) and 57 to final (LATE) feeding periods. During the early phase, combination implants caused better ADG and feed/gain than Ralgro implants (P<.001). Synovex Plus tended (P<.095) to cause higher ADG than Revalor-S. During the late phase, re-implanted steers grew faster (P<.012) and more efficiently (P<.006) than single implant steers (Table 4). Interactions existed because the magnitude of response to implants differed between groups. It could be argued that this is merely an artifact of this experiment. It may also be that cattle respond differently to these implants based upon their relative size when implants are administered.

Table 4. Breakout of Interactions between Implant Treatment & Cattle Type

Implants increased hot carcass weight (HCW) by 65 lb. The carcass produced by implanted steers were of comparable weight (Table 5). The dressing percentage was affected when comparing Synovex Plus and Revalor-S. This may be due to differences in DMI at the termination of the feedlot study.

Table 5. Effect of Implant Treatment on Carcass Traits

^a4.0 = select; 5.0 = small.

^b,c100 = A; 200 = B.

^dScale 0 to 3; 3 = stag.

^eP = .002 by Chi square analysis.

Longissimus area was increased (P<.001) by implants. There was no appreciable influence on ribfat thickness. Bone maturity and masculinity were increased by implants. Bone and lean maturity were greater for re-implanted than single-implanted cattle, but the magnitude of difference is probably inconsequential as regards carcass value.

Influences on marbling were more distinctive. Implants reduced marbling scores and percentage Choice carcasses (Table 5). Marbling scores were lower (P<.05) for single implant strategies (Synovex Plus and Revalor-S) than the re-implant strategy. These influences were more pronounced in the leaner cattle of Group II (Table 6). As was noted earlier regarding late gain responses, cattle may be responding differently to implants based on their relative size when implants are administered.

Table 6. Marbling Scores and Choice % by Implant X Cattle Source^ab

TREATMENT

^aTreatment effect (P<.001).

^bGroup effect (P<.05).

^cTreatment effect P=.002.

^dGroup effect P=.09.

^eGroup effect (P<.001).

A desirable approach to addressing implant payout would be to evaluate changes in interim period feed/gain. In this data set (as in many others that I have reviewed) there are dynamic fluctuations in feed/gain within treatment during latter stages of the feeding period. This problem becomes exaggerated with short intervals of BW change. Coupled with this problem is the fact that the Group I steers achieved the marketing target at less than 140 days. Because of these circumstances, ADG and feed/gain were not effective indicators of implant response curves.

The interim ADG, DMI and feed/gain were not useful for explaining differences in marbling scores attributable to implant treatment. When intake was re-evaluated as DMI, g/kg BW.⁷⁵, the only distinctive separation that occurred was much lower relative DMI for non-implanted steers. This response began to appear after 112 days on feed (Figure 1).

Gain energy density (GED) was calculated as NEg (Mcal)/live weight gain (lb). It is a somewhat arbitrary number. The NEm and NEg were based upon tabular values for feedstuffs