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 Sourceab

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 also would 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.

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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

Step 1

Step 2

Step 3

Step 4

Step 5

Step 5a

Corn Silage

55.00

35.00

25.00

15.00

10.00

Oat Silage

8.00

Whole Shelled Corn

26.65

40.65

47.65

54.65

57.65

59.65

High Moisture Corn

9.75

15.75

18.00

21.00

23.00

23.00

LS460b

3.50

3.50

4.25

4.25

4.25

4.25

Soybean Meal, 44%c

5.00

5.00

5.00

5.00

5.00

5.00

Limestonec

.10

.10

.10

.10

.10

.10

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.

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Table 2. Processing Schedule

Group I

Group II

DOF

Date

DOF

Date

Procedure

-2

April 29

-2

May 21

Allotment weight

-1

April 30

-1

May 22

Sort to pens

0

May 1

0

May 23

Initial BW1

1

May 2

1

May 24

Initial BW2, implant

28

May 30

28

June 21

BW, palpate implant

56

June 27

56

July 19

BW, Re-implant (4)

89

July 30

89

August 21

BW, palpate implant

112

August 22

112

September 13

BW

130

September 9

130

October 1

BW

131

September 10

   

BW

   

144

October 15

BW

   

145

October 16

BW

 

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.

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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.

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Table 3. Pooled Performance Summary

TREATMENT

CONTRAST p<

Control
(1)
Synovex Plus
(2)
Revalor-S
(3)
Ralgro
Revalor-S
(4)
SEM 1 vs. 2,3,4 2,3 vs. 4 2 vs. 3 TRT*BLK
Initial BW 721 721 722 722 1.7 NSa NS NS NS

1-28 d

BW 28

839

864

856

848

3.4

.001

.007

.120

NS

ADG

4.23

5.10

4.81

4.49

.110

.001

.002

.073

NS

DMI

17.54

17.92

17.92

17.82

.257

NS

NS

NS

NS

F/G

4.23

3.57

3.81

3.99

.095

.001

.015

.082

NS

29 to 56 d

BW 56

953

1002

993

973

4.3

.001

.001

.129

NS

ADG

4.05

4.94

4.87

4.46

.114

.001

.004

NS

.005

DMI

20.82

21.63

21.03

21.38

.287

.124

NS

.148

NS

F/G

5.15

4.40

4.33

4.85

.091

.001

.001

NS

.001

57 to 89 d/p>

BW 89

1076

1146

1140

1122

4.8

.001

.001

NS

NS

ADG

3.75

4.37

4.47

4.49

.106

.001

NS

NS

NS

DMI

22.27

23.40

23.32

23.12

.279

.004

NS

NS

NS

F/G

6.01

5.39

5.24

5.18

.129

.001

NS

NS

.149

90 to 112 d

BW 112

1136

1223

1222

1207

6.3

.001

.055

NS

NS

ADG

2.61

3.36

3.55

3.73

.159

.001

NS

NS

NS

DMI

21.52

23.85

23.68

23.88

.337

.001

NS

NS

NS

F/G

8.59

7.24

6.75

6.45

.361

.001

NS

NS

NS

113 to 130 d

BW 130

1173

1277

1268

1267

6.0

.001

NS

NS

.003

ADG

2.03

2.96

2.54

3.29

.197

.001

.032

.146

.003

DMI

20.14

23.87

23.35

23.63

.227

.001

NS

.118

.001

F/G

11.14

8.85

9.89

7.49

.851

.021

.082

NS

.005

90-130 d

ADG

2.36

3.18

3.10

3.54

.113

.001

.008

NS

.005

DMI

20.90

23.86

23.53

23.76

.248

.001

NS

NS

.025

F/G

9.02

7.67

7.63

6.79

.251

.001

.009

NS

.001

Early (1-56 d)

ADG

4.14

5.02

4.84

4.48

.073

.001

.001

.095

NS

DMI

19.18

19.77

19.47

19.60

.244

.135

NS

NS

NS

F/G

4.65

3.95

4.05

4.40

.044

.001

.001

NS

.029

Late (57-end)

ADG

2.89

3.66

3.71

3.92

.073

.001

.012

NS

.004

DMI

21.41

23.66

23.47

23.51

.233

.001

NS

NS

.053

F/G

7.49

6.49

6.34

6.00

.114

.001

.006

NS

.001

Cumulative

Final BW

1191

1301

1298

1296

6.1

.001

NS

NS

.007

ADG

3.14

3.92

3.88

3.86

.039

.001

NS

NS

.001

DMI

20.51

22.07

21.85

21.93

.200

.001

NS

NS

NS

F/G

6.56

5.63

5.63

5.69

.050

.001

NS

NS

.001

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.

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4. Breakout of Interactions between Implant Treatment & Cattle Type

TREATMENT

CONTRAST p<

Control
(1)
Synovex
Plus
(2)
Revalor-S
(3)
Ralgro
Revalor-S
(4)
SEM 1 vs. 2, 3, 4 2,3 vs.4 2 vs. 3 TRT*BLK

Late (56 To End)

ADG

Group I

2.63

3.81

3.65

3.85

.073

.001

.012

NS

.004

Group II

3.15

3.50

3.78

4.00

DMI

Group I

21.23

24.26

23.80

23.30

.233

.001

NS

NS

.053

Group II

21.59

23.06

23.14

23.72

F/G

Group I

8.09

6.37

6.53

6.07

.114

.001

.006

NS

.001

Group II

6.88

6.60

6.14

5.94

Cumulative

ADG

Group I

2.93

3.95

3.75

3.68

.039

.001

NS

NS

.001

Group II

3.35

3.89

4.01

4.04

DMI

Group I

20.47

22.41

22.18

21.79

.200

.001

NS

NS

NS

Group II

20.56

21.73

21.52

22.06

F/G

Group I

6.98

5.68

5.91

5.92

.050

.001

NS

NS

.001

Group II

6.14

5.59

5.36

5.46


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.

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5. Effect of Implant Treatment on Carcass Traits
TREATMENT
CONTRAST p<
  Control
(1)
Synovex
Plus
(2)
Revalor-S
(3)
Ralgro
Revalor-S
(4)
SEM 1 vs. 2, 3, 4 2,3 vs.4 2 vs. 3 TRT*BLK

HCW, lb

717

781

785

781

5.8

.001

NS

NS

.139

DP, %

62.10

61.85

62.35

62.17

.161

NS

NS

.028

NS

REA, in2

12.77

13.86

13.82

13.64

.135

.001

NS

NS

NS

Ribfat, in.

.385

.394

.419

.390

.014

NS

NS

NS

NS

Marblinga

5.37

4.90

5.02

5.17

.082

.001

.026

NS

NS

Bone Maturityb

133

145

146

149

1.7

.001

.114

NS

NS

Lean Maturityc

141

139

136

141

1.6

NS

.054

NS

NS

Mascu-

linityd

.63

.96

1.03

1.05

.060

.001

NS

NS

.002

% Choicee

68.4

43.0

51.0

59.6

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.

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TREATMENT

Table 6. Marbling Scores and Choice % by Implant X Cattle Sourceab

Control
(1)

Synovex
Plus (2)

Revalor-S
(3)

Ralgro
Revalor-S
(4)

x

Marblinga,b

Group I

5.52

4.95

5.13

5.19

5.20

Group II

5.21

4.85

4.90

5.16

5.03

Choice,%c,d

Group I

67.4

54.0

58.0

59.2

59.6

Group II

69.4

32.0

44.0

60.0

51.3

Ribfate

Group I

.414

.430

.470

.418

.433

Group II

.356

.357

.369

.362

.361

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 and actual feed ingredient intakes. Maintenance requirements were calculated based upon the mean BW for each pen during interim periods. The NEm requirement was estimated to be increased by 10% during exposure to E2TBA implants. The final period was averaged to 138 days on feed. Higher GED values would be indicative of higher fat content in liveweight gain.

During the initial 56 days, GED was lower (P<.05) in steers exposed to E2TBA (Figure 2). Ralgro implants caused only a slight numerical decline from control values during this period. The GED content of re-implanted steers converged with the d-1 E2TBA treatment during the 57-89 and 90-112 days periods. The GED of non-implanted steers continued to climb and create an increasingly wider separation from values for implanted steers.

During the final feeding period, the GED was lower (P<.05) for re-implanted steers than for either of the d-1 E2TBA treatments. This is following a 137-day payout for the d-1 E2TBA treatments. The E2TBA implant payout for the re-implant treatment was only 81 days at this point. The difference in GED reflects more active implant activity at this late date and is consistent with expectations of implant responses over time.

If the deposition of fat as marbling is most pronounced late in the feeding period, the GED curves suggest that marbling would be highest in the non-implant steers and lowest in the re-implant steers. Consistent with this concept, marbling scores were highest (P<.001) for the non-implanted steers. However, marbling scores were higher (P<.05) for the re-implanted steers than those on the d-1 E2TBA treatments. When the pattern of GED is compared with the ranking by marbling scores, it is the early GED values that match up with rank of marbling scores. The separation that occurs between the non-implant and re-implant treatments at day 89 may be indicative of the phase of growth when marbling scores among re-implanted steers was depressed.

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Conclusions

Actual payout optimums for implants were not defined by this research. In Group I it appeared that Synovex Plus was more potent at 130 days than was Revalor-S. This observation was reversed in the Group II replication. The differences relate to an inconsistent ADG associated with the Synovex Plus treatment.

Cumulative feedlot production costs would be comparable for the implants used, in that weight gain and DMI were similar among implanted steers. There is an additional cost associated with re-implanting, but it appears that this cost would be more than offset by the increased carcass value associated with this strategy in the Group II steers. The explanation for improved grading associated with re-implanting may relate to fewer total days of TBA exposure. However, an evaluation of gain energy density suggests that it may be the influence of implants early in the feeding period that has the greatest effect on marbling scores. Theoretically this influence may be lessened in cattle carrying more flesh when placed in the feedlot. This (along with genetics) would help explain why the Choice percentage can vary dramatically among cattle receiving the same implant strategy. Consideration of this aspect of growth would be important in determining optimum payouts for implants. Future studies may reveal that Choice percentage may be dictated more so by the existing body condition when E2TBA implants are administered than by the days from implanting to harvest.

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Revalor is a registred trademark of Intervet International BV. Ralgro is a registered trademark of Intervet Inc. Synovex Plus is a  registered trademark of Zoetis W LLC