Calvin W. Booker, D.V.M., M.Vet.Sc., G. Kee Jim, D.V.M.,
P. Timothy Guichon, D.V.M., Oliver C. Schunicht, D.V.M., B.Sc.,
Rick L. Sibbel, D.V.M.

Abstract

A field trial was conducted under commercial feedlot conditions in Nebraska to evaluate the relative efficacy of three implant programs in feedlot steers. Thirty pens containing a total of 14,196 animals were processed and randomly allocated to one of three experimental groups as follows: Ralgro/Revalor-S, which was implanted with a zeranol implant (Ralgro, Intervet/Schering-Plough Animal Health, Union, New Jersey) at allocation followed by an estradiol 17ß/trenbolone acetate implant (Revalor-S, Hoechst Roussel AgriVet, Sommerville, New Jersey) at day 70 of the feeding period; Ralgro/Synovex Plus, which was implanted with a zeranol implant (Ralgro) at allocation followed by an estradiol benzoate/trenbolone acetate implant (Synovex Plus, Fort Dodge Animal Health, Overland Park, Kansas) at day 70 of the feeding period; or Synovex Plus, which was implanted with an estradiol benzoate/trenbolone acetate implant (Synovex Plus) at allocation.

Initial weight and hip height were compared on a pen basis to assess the homogeneity of the experimental groups. Outcome variables were measured on a pen basis to assess performance, carcass grading, and animal health between the experimental groups. Performance parameters were calculated on both a live-weight (live) and fixed carcass yield (carcass) basis.

The groups were considered homogeneous with respect to initial weight and hip height (p>0.05). The daily dry matter intake of the Synovex Plus group was significantly (p<0.05) higher than the Ralgro/Revalor-S and Ralgro/Synovex Plus groups. The dry matter intake-to-gain ratio (DM:G) live and DM:G carcass of the Ralgro/Revalor-S and Ralgro/Synovex Plus group were significantly (p<0.05) lower than the Synovex Plus group. There were no significant (p>0.05) differences in final weight live, final weight carcass, weight gain live, weight gain carcass, days on feed, average daily gain (ADG) live, or ADG carcass between the experimental groups.

The percent of carcasses grading USDA Quality Grade (QG) Prime and Choice in the Ralgro/Revalor-S group was significantly (p<0.05) higher than the Ralgro/Synovex Plus and Synovex Plus groups.

The percent of carcasses grading USDA QG Select in the Ralgro/Revalor-S group was significantly (p<0.05) lower then the Ralgro/Synovex Plus and Synovex Plus groups. The percent of carcasses grading USDA QG Select in the Ralgro/Synovex Plus group was significantly (p<0.05) lower than the Synovex Plus groups. There were no significant (p>0.05) differences in the percent of carcasses grading USDA QG Standard, USDA Yield Grade (YG) 1, YG 2, YG 3, YG 4, or YG 5 between the experimental groups.

The initial rider rate in the Synovex Plus group was significantly (p<0.05) higher than the Ralgro/Revalor-S and Ralgro/Synovex Plus groups. There were no significant (p>0.05) differences in bovine respiratory disease (BRD) treatment, first BRD relapse, first rider relapse, second rider relapse, overall chronicity, overall rail, overall mortality, BRD mortality, hemophilosis mortality, metabolic mortality, polyarthritis mortality, or miscellaneous mortality rates between the experimental groups.

In the economic analysis, there were advantages of $8.80 US and $6.12 US in the Ralgro/Revalor-S and Ralgro/Synovex Plus groups as compared to the Synovex Plus group. There was an advantage of $2.68 US in the Ralgro/Revalor-S group as compared to the Ralgro/Synovex Plus group.

In summary, the results of this trial indicate that it is a cost-effective management decision in feedlot steers fed for 147 days to use a Ralgro implant at processing followed by a Revalor-S or a Synovex Plus implant at Day 70 of the feeding period as compared to Synovex Plus implant at processing, due to significant (p<0.05) improvements in the dry matter intake to gain ratio and USDA quality grade and a significant (p<0.05) reduction in the number of riders. Also, the results of this trial indicate that it is a cost-effective management decision in feedlot steers fed for 147 days to use Revalor-S instead of Synovex Plus as the terminal implant when Ralgro implants are used as the initial implant, due to significant (p<0.05) improvements in USDA quality grade and lower implant costs.

Introduction

The cost-effectiveness of using estradiol 17ß/trenbolone acetate (Revalor) in feedlot steers as a single implant and as a terminal implant is well documented. ^{1, 2, 3, 4, 5, 6} In animals fed in excess of 120 days, studies have demonstrated that zeranol (Ralgro implants) is the most cost-effective initial implant, particularly when the duration of payout is 70 to 75 days, due to a significant (p<0.05) increase in the proportion of animals grading USDA Prime or Choice, ^{7, 8, 9, 10, 11} a significant (p<0.05) decrease in the rider rate, ¹¹and no significant (p>0.05) reduction in performance.^{7, 8, 9, 10, 11} Recently, an estradiol benzoate/trenbolone acetate (Synovex Plus) implant was licensed in the United States for use in feedlot steers. However, the cost-effectiveness of using Synovex Plus as a single implant or as a terminal implant compared to Revalor-S when Ralgro implants are used as the initial implant in steers fed in excess of 120 days is unknown. As a result, additional studies are necessary to generate data pertaining to the use of Synovex Plus in commercial feedlot steers fed in excess of 120 days.

The primary purpose of the study reported herein was to compare the performance, carcass grading, and animal health of commercial feedlot steers implanted with Ralgro implants on arrival at the feedlot followed by Revalor-S or Synovex Plus at day 70 of the feeding period to steers implanted with Synovex Plus on arrival at the feedlot. A secondary objective of the study was to compare Revalor-S and Synovex Plus as terminal implants in commercial feedlot steers with respect to performance, carcass grading, and animal health.

Materials and Methods
Trial Facilities

The trial was conducted in a commercial feedlot near Broken Bow, Nebraska, which has a capacity of 66,000 animals. The basic design of the feedlot is representative of standard design in Nebraska. The animals were housed in open-air, dirt-floor pens arranged side by side with central feed alleys. There are 112 large pens in the feedlot which measure approximately 300 feet by 400 feet and have a capacity of up to 600 animals. The remaining 48 pens are smaller in dimension and have animal capacities ranging from 60 to 250 animals.

There is one permanent hospital facility and one mobile hospital facility at the feedlot. Both hospital facilities have a hydraulic chute equipped with an individual animal scale, a chute-side computer for animal health data, and separation alleys to facilitate the return of animals to designated pens. The permanent hospital has six recovery pens with a total capacity of 250 animals. Adjacent to the performance hospital are three "chronic" pens with a total capacity of 400 animals and eight receiving pens with a capacity of 150 animals each. There are an enclosed processing facility and several shipping pens.

Trial Animals

The animals utilized in the study were British crossbred beef steers purchased from auction markets throughout the central and western United States. Animals were transported by truck to the feedlot after assembly at the auction market. The animals allocated to the study were approximately 12 to 14 months of age and weighed between 427 and 1,099 lb.

Upon arrival at the feedlot, the animals were moved through a hydraulic chute for a group of procedures known collectively as processing. All animals were eartagged (to provide unique, individual animal identification ) and vaccinated against infectious bovine rhinotracheitis virus (I, Lextron, Inc., Greeley, Colorado). In addition, each animal received a multivalent clostridial vaccine (Bar-Vac^® 7, Anchor Division, Boehringer Ingelheim Animal Health, Inc., St. Joseph, Missouri). Animals allocated in June 1996 received topical fenthion (Tiguvon^® {Cattle}, Bayer Corporation, Shawnee, Kansas), and animals allocated in July and August 1996 received topical ivermectin (Ivomec^® Pour-on for Cattle, Merck Agvet Division, Merck & Co., Inc., Rahway, New Jersey).

Experimental design

During the processing procedures at the feedlot, animals from each processing group were randomly assigned to one of the three experimental groups as follows: Ralgro/Revalor-S, which was implanted with a zeranol implant (Ralgro) at allocation followed by an estradiol 17ß/trenbolone acetate implant (Revalor) at day 70 of the feeding period; Ralgro/Synovex Plus, which was implanted with a zeranol implant (Ralgro) at allocation followed by an estradiol benzoate/trenbolone acetate implant (Synovex Plus) at day 70 of the feeding period; or Synovex Plus, which was implanted with an estradiol benzoate/trenbolone acetate implant (Synovex Plus) at allocation. Animals in each experimental group were assembled in designated pens until the pens were full. Replicates (one pen from each experimental group) were filled consecutively until there were 10 replicates with a total of 30 pens.

Feeding Program

A standard mixed complete feedlot diet, formulated to meet or exceed the nutritional requirements of feedlot cattle (Nutritional Requirements for Beef Cattle, National Research Council, 1996) was offered ad libitum. The experimental diets were blended by combining dry-rolled corn, high-moisture corn, corn silage, alfalfa hay, tallow, corn distiller's grain solubles, and supplement in a modern batch milling facility equipped with overhead bins.

The diets were delivered by truck-mounted mixers on load cells. The supplement was manufactured in a granular form by a commercial feed mill (Farr Better Feeds, Duncan, Nebraska). The calculated composition of the supplement is shown in Table 1.

Table 1. Calculated composition (100% dry matter basis) of the supplement

The diets were delivered to the pens once or twice daily. Daily feed allowances to each pen were recorded. Water was provided ad libitum from automatic waterers. The animals were adapted to a finisher diet over a 25- to 35-day period by increasing the proportion of dry-rolled and high-moisture corn and decreasing the proportion of corn silage and alfalfa hay. The composition of the diets fed is presented in Table 2.

Table 2. Proportional composition (100% dry matter basis) of the mixed complete diets

Diet

The supplement was manufactured in granular form by a commercial feed mill (Farr Better Feeds, Duncan, Nebraska).

These baseline data were subsequently imported into a spreadsheet program (Quattro Pro 6.0, Corel Corporation, Ottawa, Ontario) where average initial weight and average hip height were calculated for each pen.

Ingredients were sampled bi-weekly, and the dry matter content of each ingredient was determined. From these data, the ration dry matter and the dry matter intake for each pen were calculated.

Sampling

The finisher diets were sampled monthly. These samples were analyzed for crude protein, fiber, calcium (Ca), phosphorus (P), and potassium (K) (Servi-Tech Labs, Hastings, Nebraska).

Animal Health

The cattle were observed once or twice daily by experienced pencheckers. The pencheckers were blind as to the experimental status of each pen. Cattle deemed to be "sick" by the pencheckers were moved to the hospital facility, diagnosed, and treated as per the written treatment protocols provided by the consulting veterinarians. In this study, the case definition for bovine respiratory disease (BRD) was an elevated rectal temperature (> 40.3°C) and a lack of abnormal clinical signs referable to body systems other than the respiratory system. All animal health events, including treatment date, presumptive diagnosis, drug(s) used, and dosage used, were recorded on the chute-side computer system.

All animals that died during the study were necropsied. The cause of death was determined by the attending veterinarian.

Marketing

The cattle were sold under normal marketing procedures whereby the feedlot manager, based on visual appraisal, determined that a replicate (one pen from each experimental group) was ready for sale. All animals in a replicate were trucked to a packing plant for slaughter (IBP, Lexington, Nebraska) on the same day.

Data collection and management

At processing, each animal was individually weighed, and hip height was measured to assess the homogeneity of the animals in each experimental group.

The outcome variables measured to assess performance were final weight live, final weight carcass, weight gain live, weight gain carcass, days on feed (DOF), daily dry matter intake (DDMI), average daily gain (ADG) live, ADG carcass, the dry matter intake-to-gain ratio (DM:G) live, and DM:G carcass. The outcome variables measured to assess animal health were initial BRD treatment rate, first BRD relapse rate, initial rider rate, first rider relapse rate, second rider relapse rate, overall chronicity rate, overall rail rate, overall mortality rate, BRD mortality rate, hemophilosis mortality rate, metabolic mortality rate, polyarthritis mortality rate, and miscellaneous mortality rate. In addition, the yield grade (YG) and quality grade (QG) were obtained for all animals on the trial.

The outcome variables used to assess feedlot performance were calculated on a pen basis as follows.

Grading data on all carcasses were obtained at slaughter. The proportion of animals grading USDA YG 1, YG 2, YG 3, YG 4, YG 5, QG Prime or Choice, QG Select, or QG Standard was calculated for each pen. In addition, the proportion of heavy carcasses (> 950 lb.) was calculated for each pen.

The computerized animal health data were verified and summarized. From these data, risk rates for initial BRD treatment, first BRD relapse, initial rider, first rider relapse, second rider relapse, overall chronicity (animals designated as chronics), overall rail (animals railed for salvage), overall mortality (mortality due to all causes), BRD mortality (mortality due to BRD), hemophilosis mortality (mortality due to Haemophilus somnus infection), metabolic mortality (mortality due to metabolic disease), polyarthritis mortality (mortality due to polyarthritis), and miscellaneous mortality (mortality due to causes other than BRD, hemophilosis, or metabolic disease) were calculated for each pen.

Statistical analysis

The data were analyzed using an analytical software program (The SAS‰ System for Windows, Release 6.11, SAS Institute Inc., Cary, North Carolina).

The chemical analyses of the mixed complete diets were compared between the experimental groups using least squares analysis of variance.¹²

The baseline, performance, and carcass grading variables were compared between the experimental groups using least squares analysis of variance for replicate and treatment effects.¹²The baseline variables were tested as covariates of the performance parameters. Those covariates with significant (p< 0.05) effects were included in the final model used for comparison of each parameter between the experimental groups.

The animal health parameters were compared between the experimental groups using linear logistic regression modeling techniques controlling for intra-pen clustering of disease using the method described by Van Donkersgoed, Ribble, Boyer, and Townsend¹⁴and reviewed by McDermott, Schukken, and Shoukri.^15,16

Economic analysis

The relative cost-effectiveness of the experimental groups was calculated using a computer spreadsheet program (Quattro Pro 6.0, Corel Corporation). In the economic model, the initial weight, final weight, ADGC, feeder price, slaughter price, Choice-Select spread, ration cost, yardage rate, mortality rate, and interest rate were fixed for all experimental groups. The implant costs, including the cost of administering the terminal implant, used in the economic analyses for the Ralgro/Revalor-S, Ralgro/Synovex Plus, and Synovex Plus groups were $5.27 US, $5.52 US, and $3.60 US, respectively. The veterinary costs used in the economic analyses were $4.00 US, $4.00 US, and $4.25 US for the Ralgro/Revalor-S, Ralgro/Synovex Plus, and Synovex Plus groups, respectively, reflecting the significant (p< 0.05) difference in the initial rider rates between the experimental groups. The actual DM:G carcass, percent of carcasses grading USDA QG Prime and Choice, and the percent of carcasses grading USDA QG Select were used in the economic model when significant (p< 0.05) differences between experimental groups existed. When no significant (> 0.05) differences existed between the experimental groups for these parameters, the parameters were standardized.

Results

The chemical analysis of the mixed complete diets is shown in Table 3.

Table 3. Chemical analysis (100% dry matter basis) of the mixed complete diets by experimental group

Experimental Group

Chemical analysis performed by Servi-Tech Labs, Hastings, Nebraska

There were no significant differences (p> 0.05) in the levels of crude protein, fiber, Ca, P or K between the experimental groups.

The pen-based summary statistics for the baseline, performance, and carcass grading parameters are presented in Tables 4, 5 and 6, and 7, respectively.

The groups were considered homogeneous with respect to average initial weight and average frame size (p> 0.05) (Table 4).

Table 4. Baseline data summary

Experimental Group

1. Initial weight for each pen was calculated as the summation of the individual animal initial weights corrected for the shrink from purchase to arrival at the feedlot.

2. Hip height is the average hip height within each pen.

The daily dry matter intake of the Synovex Plus group was significantly (p<0.05) higher than the Ralgro/Revalor-S and Ralgro/Synovex Plus groups. The dry matter intake-to-gain ratio (DM:G) live and DM:G carcass of the Ralgro/Revalor-S and Ralgro/Synovex Plus groups were significantly (p<0.05) lower than the Synovex Plus group. There were no significant (p>0.05) differences in final weight live, final weight carcass, weight gain live, weight gain carcass, days on feed, ADG live, or ADG carcass between the experimental groups (Tables 5 and 6).

Table 5. Performance data summary based on live weight

Experimental Group

a, b Means in the same row with different superscripts are significantly (p<0.05) different.

1. Final Weight Live for each pen was calculated as the total live weight out divided by the number of animals sold.

2. Weight Gain Live for each pen was calculated as (total live weight out plus total weight deads minus total weight in) divided by the initial number of animals in the pen.

3. DOF is the number of days on feed and for each pen was calculated as the average days occupation in the feedlot.

4. DDMI is the pounds of feed consumed per animal per day expressed on a 100% dry matter basis.

5. ADG Live is the average number of pounds gained per day during the feeding period based on live weight.

6. DM:G Live is a ratio of the pounds of feed (expressed on a 100% dry matter basis) necessary for 1 pound of gain based on live weight.

Table 6. Performance data summary based on carcass weight

Experimental Group

a, b Means in the same row with different superscripts are significantly (p<0.05) different.

1. Final Weight Carcass for each pen was calculated as ({total carcass weight out divided by a fixed carcass yield of 63.0%} plus total live weight rails) divided by the number of animals sold.

2. Weight Gain Carcass for each pen was calculated as ({total carcass weight out divided by a fixed carcass yield of 63.0%} plus total live weight rails plus total live weight deads minus total weight in) divided by the initial number of animals in the pen.

3. DOF is the number of days on feed and for each pen was calculated as the average days occupation in the feedlot.

4. DDMI is the pounds of feed consumed per animal per day expressed on a 100% dry matter basis.

5. ADG Carcass is the average number of pounds gained per day during the feeding period based on carcass weight.

6. DM:G Carcass is a ratio of the pounds of feed (expressed on a 100% dry matter basis) necessary for 1 pound of gain based on carcass weight.

Table 7. Carcass grading data summary

Experimental Group

a,b,c Means in the same row with different superscripts are significantly (p<0.05) different.

1. Yield Grade 1 is the proportion of animals within a pen that graded USDA Yield Grade (YG) 1.

2. Yield Grade 2 is the proportion of animals within a pen that graded USDA YG

3. Yield Grade 3 is the proportion of animals within a pen that graded USDA YG

4. Yield Grade 4 is the proportion of animals within a pen that graded USDA YG

5. Yield Grade 5 is the proportion of animals within a pen that graded USDA YG

6. Quality Grade Choice is the proportion of carcasses within a pen that graded USDA Quality Grade (QG) Choice or Prime.

7. Quality Grade Select is the proportion of carcasses within a pen that graded USDA QG Select.

8. Quality Grade Standard is the proportion of carcasses within a pen that graded USDA QG Standard.

9. Heavy Carcasses is the proportion of animals within a pen that had carcasses greater than 950 lb.

The percent of carcasses grading USDA QG Prime and Choice in the Ralgro/Revalor-S group was significantly (p<0.05) higher than the Ralgro/Synovex Plus and Synovex Plus groups. The percent of carcasses grading USDA QG Select in the Ralgro/Revalor-S group was significantly (p<0.05) lower than the Ralgro/Synovex Plus and Synovex Plus groups. The percent of carcasses grading USDA QG Select in the Ralgro/Synovex Plus group was significantly (p<0.05) lower than the Synovex Plus groups. There were no significant (p>0.05) differences in the percent of carcasses grading USDA QG Standard, USDA YG 1, YG 2, YG 3, YG 4, or YG 5 between the experimental groups (Table 7).

The distribution of new rider cases by weeks on feed is presented in Figure 1.

Figure 1. Distribution of New Rider Cases by Weeks on Feed

The initial rider rate in the Synovex Plus group was significantly (p<0.05) higher than the Ralgro/Revalor-S and Ralgro/Synovex Plus groups. There were no significant (p>0.05) differences in bovine respiratory disease (BRD) treatment, first BRD relapse, first rider relapse, second rider relapse, overall chronicity, overall rail, overall mortality, BRD mortality, hemophilosis mortality, metabolic mortality, polyarthritis mortality, or miscellaneous mortality rates between the experimental groups (Tables 8 and 9).

Table 8. Morbidity data summary

Experimental Group

a,b Means in the same row with different superscripts are significantly (p<0.05) different.

1. Initial BRD Treatment Rate is the average proportion of animals in each pen initially treated for bovine respiratory disease (BRD).
   
   
2. First BRD Relapse Rate is the average proportion of animals treated for BRD in each pen that relapsed.
   
   
3. Initial Rider Rate is the average proportion of animals in each pen treated as riders.
   
   
4. First Rider Relapse Rate is the average proportion of animals in each pen treated as riders that relapsed.
   
   
5. Second Rider Relapse Rate is the average proportion of first rider relapses in each pen that relapsed a second time.
   
   
6. Overall Chronicity Rate is the average proportion of animals in each pen designated as chronics.
   
   
7. Overall Rail Rate is the average proportion of animals in each pen that were railed for salvage.

Table 9. Mortality data summary

Experimental Group

1. Overall Mortality is the average proportion of animals in each pen dying due to all causes.
   
   
2. BRD Mortality is the average proportion of animals in each pen dying due to BRD.
   
   
3. Hemophilosis Mortality is the average proportion of animals in each pen dying due to Haemophilus somnus infection.
   
   
4. Metabolic Mortality is the average proportion of animals in each pen dying due to metabolic disease.
   
   
5. Polyarthritis Mortality is the average proportion of animals in each pen dying due to polyarthritis.
   
   
6. Miscellaneous Mortality is the average proportion of animals in each pen dying due to causes other than BRD, hemophilosis, metabolic disease, or polyarthritis.

Acknowledgments

This project was wholly supported by a research grant from Mallinckrodt Veterinary, Inc., Mundelein, Illinois. We thank the management and staff of Adams Land & Cattle Co., Broken Bow, Nebraska for their assistance and cooperation in conducting this study.

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