HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Schlegel, M. L. Articles by Rust, S. R. Search for Related Content PubMed PubMed Citation Articles by Schlegel, M. L. Articles by Rust, S. R.

Use of bovine somatotropin for increased skeletal and lean tissue growth of Holstein steers^1,2,3

M. L. Schlegel^*,4, W. G. Bergen^*,5, A. L. Schroeder, M. J. VandeHaar^* and S. R. Rust^*,6

^* Department of Animal Science, Michigan State University, East Lansing 48824-1225; and Elanco Animal Health, Greenfield, IN 46140

	Abstract

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION IMPLICATIONS LITERATURE CITED

 
One hundred-sixty Holstein growing-finishing steers (initial BW of 185 kg) were blocked by BW to determine the effectiveness of long-term bovine somatotropin (bST) administration on lean, skeletal, and carcass measurements. Steers were randomly allocated to 4 treatments (10 steers/treatment) within a block (n = 4 blocks). Treatments were control, no bST (C-C); bST from d 0 to 182 (bST-C); bST from d 183 to slaughter (C-bST); and bST from d 0 to slaughter (bST-bST). Steers received a s.c. injection of placebo or bST at 14-d intervals. Doses were 320 mg of bST/injection from d 0 to 112 and 640 mg of bST/injection from d 113 to slaughter. The last treatment was administered 31 d before slaughter. Steers received a 14% CP (DM basis) diet from d 0 to 182 and 11.5% CP from d 183 to slaughter that consisted of dry, whole-shelled corn and a pelleted protein-mineral supplement. Steers were slaughtered when BW per block averaged 615 kg (d 325, 353, 367, and 381 for the 4 blocks, respectively). Thirty steers were removed from the study because of poor performance with respect to their pen mates, illness, lameness, death, incomplete castration, and incorrect treatment. Serum IGF-I concentrations increased 151% (P < 0.01) from d 7 through 35 in bST-treated steers compared with control steers. During the first 182 d, bST-C and bST-bST steers were heavier (P < 0.01) and had greater (P < 0.01) ADG, G:F, hip height, and hip height gain compared with C-C and C-bST steers. From d 183 to slaughter, C-bST steers had reduced (P < 0.05) daily DMI and greater G:F than bST-C steers. At final slaughter, C-bST and bST-bST steers had greater (P < 0.05) hip height than C-C steers. Noncarcass weight was increased and dressing percent reduced (P < 0.05) in C-bST and bST-bST steers compared with C-C steers. Quality grade was least (P < 0.05) in bST-bST carcasses compared with C-C, whereas bST-C and C-bST carcasses were intermediate. At final slaughter, steers receiving bST had greater (P < 0.05) carcass protein and water composition and lower (P < 0.05) carcass lipid and lipid accretion than C-C steers. Bovine somatotropin was effective in reducing carcass fat and increasing edible lean. Administering bST to young, lightweight steers increased skeletal growth and noncarcass weight without an increase in total carcass weight, but decreased carcass quality.

Key Words: carcass measurement • Holstein • lean • skeletal growth • somatotropin • steer

	INTRODUCTION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION IMPLICATIONS LITERATURE CITED

 
A greater awareness and demand by consumers for healthier beef products has prompted the beef industry to emphasize production of lean beef, which maintains consumer acceptance. Identification of production strategies that accomplish this goal has led researchers to investigate exogenous growth promotants such as bovine somatotropin (bST).

Research has documented the ability of bST to stimulate growth and reduce carcass lipid content in pigs (Krick et al. 1993), lambs (Butler-Hogg and Johnsson, 1987), steers (Moseley et al., 1992; Preston et al., 1995; Rumsey et al., 1996), and bull calves (Holzer et al., 1999). Previous results in beef cattle administered bST have demonstrated greater increases in noncarcass weight than lean and skeletal tissue (Early et al., 1990a). Additionally, as cattle fed high-concentrate diets increase in weight and age, carcass lipid mass increases at a greater rate than carcass protein (Owens et al., 1995). Administration of bST to younger animals during peak periods of lean and skeletal tissue growth may increase the effectiveness of the exogenous hormone to alter carcass lipid and protein content. Therefore, a study was designed to evaluate the effectiveness of long-term bST administration to growing-finishing Holstein steers on lean, skeletal, and organ growth, and also on carcass characteristics and composition, and serum IGF-I concentrations.

	MATERIALS AND METHODS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION IMPLICATIONS LITERATURE CITED

 
Animal Management
This study was completed with the approval of the Michigan State University All University Committee on Animal Use and Care (AUF # 10/90-308-02) and under an investigational new animal drug application (6673-C004 - bST) issued to Michigan State University. Sixty-four to 71 d before beginning the study, 243 Holstein steers (116 kg) were received from Indiana and Wisconsin at the Beef Cattle Teaching and Research Center in East Lansing, MI. Upon arrival, steers were placed in partially covered pens (4.3 x 11.9 m, 10 to 12 steers per pen) and fed 1.36 kg of dry, whole-shelled corn, 0.91 kg of medicated-pelleted supplement (Rebound supplement; Kent Feeds, Inc., Muscatine, IA), and had ad libitum access to second cutting alfalfa hay and water. Steers were ear-tagged, vaccinated against infectious bovine rhinotracheitis, parainfluenza-3, bovine viral diarrhea, bovine respiratory syncytial virus (Vira Shield 4; Grand Laboratories, Inc., Larchwood, IA), and mass medicated with 10 mL of an antibiotic mixture (225 mL of long-acting penicillin, 225 mL of spectinomycin, and 50 mL of vitamin B complex). Animals with rectal temperatures of 40°C or higher were treated for 2 additional days with the described antibiotic mixture.

Two weeks after arrival, steers received booster vaccinations and also received initial vaccinations against Haemophilus somnus and Pasteurella haemolytica-multocida (Bioceutic, St. Joeseph, MO) and Clostridial organisms (Ultrabac-7; Beecham Laboratories, Piscata-way, NJ; or Fermicon-8; Bioceutic, St. Joseph, MO). Additionally, steers were mass medicated with oxytetracycline (10 mL/steer, 100 mg/mL of oxytetracycline), checked for growth promotant implants, and dehorned. Any animals that were found not to be castrated were subsequently castrated.

Thirty-four days before the initiation of the study, the medicated supplement was removed from the diet and replaced by a 50% CP pellet (Table 1), and steers were given a 2 mL injection of vitamin E and selenium (Mu-Se; Schering-Plough Animal Health, Kenilworth, NJ). The steers were fed a 14% CP (DM basis) diet consisting of 86% dry, whole-shelled corn and 14% pelleted supplement (Table 1) until the initiation of the study.

Steers were housed in partially covered pens (4.3 x 11.9 m) with ad libitum access to feed and water. The diet consisted of dry, whole-shelled corn and a pelleted supplement (Table 1). During the first 182 d, steers received a 14% CP diet, and from d 183 to final slaughter, steers received an 11.5% CP diet.

To address the objective of strategic timing of bST administration, 64 steers remained on their initial treatment after d 182 or were switched to the opposite treatment to provide the 4 different treatment groups as previously described. Two steers from each pen (32 steers total, 16 control, 16 bST treated) were randomly selected for slaughter when treatments were changed on d 182 (intermediate slaughter). The intermediate slaughter steers received their last treatment injection on d 168 (last effective dose on d 182) and remained with their treatment group until d 199, when steers were transported to a commercial-slaughter facility. Final slaughter of steers was conducted when weight blocks were predicted to reach 615 kg and a 31-d withdrawal period from last treatment was observed as required by the investigational new animal drug application. Blocks were transported to a commercial slaughter facility for final slaughter on d 325, 353, 367, and 381; final weights were 611, 609, 602, and 619 kg, respectively.

If a steer gained (ADG) less than 50% of its penmates for 2 consecutive weigh periods (28 d), the steer was removed from the study. Thirty steers were removed from the study. These included 22 steers for gaining 50% less than their pen mates, 3 for respiratory problems, 2 because of death, 1 for lameness, 1 for incomplete castration, and 1 for incorrect treatment before slaughter (7, 7, 7, and 9 steers were removed from C-C, bST-C, C-bST, and bST-bST, respectively).

Preparation and Administration of Treatments
Bovine somatotropin (Lilly Research Laboratories, Greenfield, IN) and control treatments were preloaded in 10 mL syringes and frozen until used. The carrier agent was white wax. One hour before administration, the required number of bST and control treatments were thawed at room temperature. Steers received a s.c. control (placebo) or bST injection (16-gauge needle) at 14-d intervals beginning on d 0. From d 1 to 42, injections were administered in the midthoracic region just caudal to the shoulder, on alternating sides. From d 43 to slaughter, treatments were given s.c. in the perirectal area. Dosages of bST administered were 320 mg of bST/injection (22.9 mg/d, lot # 48631) from d 0 to 112 and 640 mg of bST/injection (45.7 mg/d, lot # 48632) from d 113 to slaughter. The change in dosage after 112 d was as directed by the sponsor and helped maintain the bST dose relative to BW. Control steers received a similar volume of carrier agent as that given to the bST-treatment steers. Treatments were administered between 0730 and 1100.

Blood Collection and Serum IGF-I Assay
Blood samples were collected on d 0, 7, 14, 21, 28, and 35 at the beginning of the study and before slaughter 7, 14, 21, and 28 d after the last treatment. To reduce the influence of bST spikes on IGF-I concentrations, the evening before blood collection, steers were removed from feed for 16 h and the next morning were fed 0.5 h before blood collection by jugular venipuncture. Blocks (4 pens) were staggered every 1 h with feeding begun at 0700. Blood (10 mL) was collected, and serum was harvested and stored at –20°C.

Serum IGF-I concentrations were measured on 2 randomly selected steers from each pen by radioimmunoassay after removal of IGF-binding proteins by formic acid-ethanol extraction (Sharma et al., 1994). The international human IGF-I reference served as the standard; this standard gives IGF values twice that of most recombinant standards (Bristow et al., 1990).

Feedlot Performance
Initial, intermediate (d 182), and final weights were calculated as the average of weights taken on 2 consecutive days. Interval weights were determined every 14 d. Orts were weighed weekly to determine daily DMI. Feed efficiency (G:F) was calculated as ADG (g) divided by daily DMI (kg) for a specific time period.

Skeletal Growth
Skeletal growth was assessed through hip-height measurements (Altitude Stick; NASCO, Fort Atkinson, WI) on d 0 and 1 (averaged for initial hip height), d 181 and 183 (averaged for d 182 hip height), and on 2 consecutive days before slaughter (averaged for final hip height). Skeletal growth (cm/d) was calculated for each period (d 0 to 182, d 183 to slaughter, and d 0 to slaughter) of the study.

At slaughter, the right front limb was separated from the carcass proximal to the carpo-metacarpal joint (knee), placed in a labeled plastic bag, and returned to the Michigan State University Meat Laboratory for dissection. The hide, tendons, ligaments, muscle, and fat were removed from the bones, and the metacarpal bone was separated from the carpus and phalanges. The metacarpus was frozen for future analyses. Third metacarpal bone length was determined, and the bones were sectioned at their midpoint and measurements obtained according to Coble et al. (1971). Medial and lateral width and depth, and circumference of the bone section, were determined. Total cross-sectional area and marrow cavity area were determined using a compensating polar planimeter (Keuffel and Esser Co., Germany). Bone area was determined as the difference between total cross-sectional area and marrow cavity area. Bone volume was determined by water displacement and used to calculate bone density (g/mL).

Carcass Measurements
At slaughter, hot carcass, lungs, liver, spleen, heart, kidney, and semitendinosus muscle were weighed. After a 24-h postslaughter chill, the ribeye area, 12th-rib backfat, KPH, marbling score, and USDA quality grade were determined. Noncarcass weight, dressing percent, and yield grade were calculated (Boggs and Merkel, 1993). Noncarcass weight was calculated as the difference between the final slaughter weight and HCW. The 9th through 13th rib sections were removed from the left side of the carcasses for compositional determination and transported to the Michigan State University Meats Laboratory. The 9th through 11th rib sections were separated from the larger rib portion (Hankins and Howe, 1946), weighed, and the soft tissue was separated from bone. Bones and soft tissue from each rib were weighed. The soft tissue was ground in a Hobart meat grinder (Horbart Corp., Troy, OH) 3 times (once coarsely and twice finely) with mixing in between each grind to ensure uniformity. Approximately 500 g of sample was collected and placed into a Whirlpak bag (NASCO, Fort Atkinson, WI) and stored at –30°C. The frozen sample was homogenized with liquid N in an industrial Waring blender. Tissue samples were analyzed for DM, CP, and ether-extractable lipid.

Tissue sample DM was determined in triplicate by placing 2 g of homogenized tissue in a desiccated labeled aluminum pan (5 cm diameter) and dried for 48 h in a 55°C oven. Tissue moisture was determined by difference. Ether-extractable lipid was determined in triplicate using samples previously dried. A cotton ball was placed in the center of each aluminum pan, and the sides were folded inward to prevent loss of sample and the cotton ball. The dried samples were placed in a Soxhalet apparatus and extracted with petroleum ether for 24 h. Ether-extractable lipid was calculated as the loss of weight during ether extraction.

Crude protein was analyzed in duplicate for total-Kjeldahl N (AOAC, 1984) using a Technicon auto-analyzer system (Bran + Luebbe Inc., Tarrytown, NY). The proportions of carcass bone, lipid, protein, and moisture were calculated based on equations by Hankins and Howe (1946). Accretion rates of lipid and protein were determined from equations developed by Anderson et al. (1988) using initial slaughter data for accretion rates from d 0 to 182 and average treatment intermediate slaughter data for accretion rates from d 183 to slaughter.

Statistical Analysis
The study was designed as a randomized complete block. Feedlot performance (BW, ADG, DMI, and G:F) was analyzed with the GLM procedure of SAS (SAS Inst. Inc., Cary, NC) with block and treatment in the model and the pen as the experimental unit. Means for traits evaluating performance from d 0 to 182 were separated using a contrast statement to determine the difference between control (C-C and C-bST) and bST (bST-C and bST-bST) treatments during the first phase of the study. Performance trait means from d 183 to slaughter and from d 0 to slaughter were separated using a Tukey’s test for all pairwise comparisons.

Hip height, hip-height gain, metacarpal bone characteristics, carcass characteristics, carcass composition, and tissue weights were analyzed with the GLM procedure of SAS with block and treatment in the model and the animal as the experimental unit. A significant block x treatment interaction (P < 0.10) was included in the model for hip-height gain from d 0 to 182, intermediate slaughter spleen weight (g), intermediate slaughter bone characteristics (medial bone depth, lateral bone depth, and bone area), and final slaughter liver weight (g, g/kg of HCW). Least square treatment means were calculated and separated using the PDIFF ADJUST= TUKEY option. Treatment means were only separated if the overall treatment F statistic was significant (P < 0.10). To separate the percentages of carcasses in USDA quality grades, the Fisher’s exact test of SAS was used.

Serum IGF-I concentrations were analyzed using the univariate repeated-measures analysis of SAS with block and treatment in the model and using the animal as the experimental unit. Treatment means within a day were separated by procedures outlined by Gill (1988).

One control steer, from the intermediate slaughter group, was removed from the study because it received an incorrect treatment 3 d before slaughter. All individual data from this steer and the data from an additional 29 steers previously removed from the study were omitted.

	RESULTS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION IMPLICATIONS LITERATURE CITED

 
Serum IGF-I Concentrations
Steers receiving bST had 151% greater (P < 0.01) serum IGF-I concentrations from d 7 through d 35 of the study compared with control steers (Figure 1). After the final treatment injection, 31 d before slaughter, C-bST and bST-bST steers had 298 and 223% greater (P < 0.05) serum IGF-I concentrations 7 and 14 d after the last treatment, respectively, than C-C and bST-C steers (Figure 2). Twenty-one days after the last treatment, bST-bST steers had 163% greater (P < 0.05) serum IGF-I concentrations than C-C, bST-C, and C-bST steers. Serum IGF-I concentrations were not different among all steers 28 d after the last treatment injection.

View larger version (14K): [in this window] [in a new window]   Figure 1. Effect of treatment, control [circle; no bovine somatotropin (bST) treatment from d 0 to slaughter; and no bST treatment from d 0 to 182 and d 183 to slaughter] or bST (square; bST treatment from d 0 to 182 and no bST from d 183 to slaughter; and bST treatment from d 0 to slaughter), on serum IGF-I concentrations after initial treatment on d 0 and subsequent treatments as indicated by arrows. a,bMeans without common superscript letters differ (P < 0.01; SED = 40.1).

View larger version (15K): [in this window] [in a new window]   Figure 2. Effect of treatment, no bovine somatotropin (bST) treatment from d 0 to slaughter (open circle), no bST treatment from d 0 to 182 and bST from d 183 to slaughter (closed circle), bST treatment from d 0 to 182 and no bST from d 183 to slaughter (open square), or bST treatment from d 0 to slaughter (closed square), on serum IGF-I concentrations after final treatment 31 d before final slaughter as indicated by the arrow. a,bMeans without common superscript letters differ (P < 0.05; SED = 91.9).

Feed efficiency was 9% greater (P < 0.001) in bST-treated steers (bST-C and bST-bST) during the first 182 d compared with steers receiving no bST during the first 182 d (C-C and C-bST). Steers receiving bST only during the latter phase of the study (C-bST) had 25.6% greater (P < 0.05) G:F than bST-C steers, and 6.8% greater (P < 0.05) overall G:F overall than C-C steers.

Skeletal Growth
On d 182, hip height was increased 1.2% (P < 0.01) in steers receiving bST during the first phase of the study (Table 3). Steers receiving bST during the entire study (bST-bST) had 3.3 and 2.2% greater (P < 0.05) hip heights at slaughter than C-C and bST-C, respectively. Steers receiving bST only during the latter phase of the study (C-bST) had 1.8% greater (P < 0.05) hip heights at slaughter than C-C steers. Daily hip height gain was increased (P < 0.001) by 8% in steers receiving bST during the first 182 d (bST-C and bST-bST) compared with steers receiving no bST during the first 182 d (C-C and C-bST). Steers receiving bST during the latter phase of the study (C-bST and bST-bST) had 66% greater (P < 0.05) daily hip-height gain from d 182 to slaughter than C-C and bST-C steers. Overall (d 0 to slaughter), bST-bST steers had 15, 7, and 10% greater (P < 0.05) daily hip-height gain than C-C, C-bST, and bST-C steers, respectively.

Semitendinosus muscle, liver, lung, and spleen weights did not differ among treatments at the intermediate-slaughter point (data not shown). Steers receiving bST during the first phase of the study had smaller (P < 0.05) hearts relative to BW than C-C steers, but bST steers tended to have larger (P < 0.10) kidney weights on an absolute (9.2%) and relative (7.1%) basis than C-C steers (data not shown).

At the conclusion of the study, steers receiving bST in the later phase of the study (C-bST and bST-bST) tended to have 7% greater (P < 0.10) semitendinosus muscle weight relative to HCW than C-C steers (Table 7). Spleen weights of bST-bST steers were 7.5% greater (P < 0.05) than C-C steers. Kidney weights were 23 and 12.6% greater (P < 0.05) in bST-bST steers than C-C and bST-C steers, respectively. Relative to BW, bST-bST steers had 18.9% greater (P < 0.05) kidney weights than C-C steers.

	DISCUSSION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION IMPLICATIONS LITERATURE CITED

 
Serum IGF-I Concentration
An increase in serum IGF-I concentration in bST-treated steers is consistent with previous research conducted in feedlot cattle (Moseley et al., 1992; Preston et al., 1995; Holzer et al., 2000), but the magnitude was comparable to the 91 to 200% increase in serum IGF-I concentrations in bST-treated dairy heifers (Yung et al., 1996) and late-lactation dairy cows (Sharma et al., 1994), respectively. After 22 wk of bST administration to steers, Enright et al. (1990) demonstrated that IGF-I concentrations returned to control concentrations 5 days after the last treatment of 40 µg of bST/kg of BW. In the current study, IGF-I concentration returned to baseline 14 to 28 d after the last bST treatment; the delay to return to control concentrations was probably due to an increased dosage (averaged 88 µg of bST/kg of BW) used in the later phase of the current study.

Feedlot Performance
After 182 d of treatment, steers receiving bST had greater BW than control steers. This is in agreement with short-term studies using steers (Early et al., 1990a; Rumsey et al., 1996) and bull calves (Holzer et al., 1999) of similar initial BW. When treatments were continued in the current study and steers were slaughtered between 325 and 381 d on feed, steer BW were not different. Final BW of steers were also not different when steers with heavier initial BW (378 kg) received bST treatment (Preston et al., 1995).

Previous research has shown a 3.5 to 28% increase in ADG of feedlot steers (Early et al., 1990a; Preston et al. 1995; Rumsey et al., 1996) and bull calves (Holzer et al., 1999) with bST administration. Additionally, Moseley et al. (1992) demonstrated that bST doses between 16.5 and 33 µg of bST/kg of BW increased ADG, but doses of 100 and 300 µg of bST/kg of BW decreased ADG of steers weighing 392 to 418 kg. In the current study we observed an 8.9% increase in ADG within the first 182 d of the study, but ADG were not different during the later phase of the study.

The inconsistent effect of bST on DMI in the current study is comparable to the results of previous studies (Early et al., 1990a; Preston et al., 1995; Rumsey et al., 1996). McBride and Moseley (1991) suggest that in animals that may have deposited fat, the administration of bST increases the amount of circulating nutrients, which cannot be fully utilized by the animal; therefore, to compensate the animal reduces its DMI. In the current study, the largest decrease in intake was observed in C-bST steers, which only received bST during the later phase of the study. These steers had greater body fat than the bST-bST and bST-C steers after 182 d of bST administration, and therefore would fit the theory suggested by McBride and Moseley (1991). As a result of either increased ADG or decreased DMI, the current study demonstrated an increase in feed efficiency (G:F) during all phases of the study when steers received bST for a period of time during the study. The increase in efficiency is in agreement with previous studies using steers (Early et al., 1990a; Preston et al., 1995; Rumsey et al., 1996) and bull calves (Holzer et al., 1999).

Skeletal and Bone Growth
Hip height increased 5 cm (3.3%) from C-C to bST-bST steers and was moderately correlated with metacarpal length. Loy et al. (1988) also observed an increase in hip height in estrogen-implanted steers over controls steers without a corresponding increase in metacarpal length. Early et al. (1990b) observed a 1.3 cm increase in humerus length in steers administered bST, but not in the length of the femur, tibia, or radius.

Bovine somatotropin administration increased the percentage of bone in the carcass. This is in agreement with research in feedlot steers (Dalke et al., 1992; Rathmacher et al., 1997) and ewe lambs (Johnsson et al., 1985) receiving bST. Additionally, daily growth in bone circumference was observed in the femur of steers treated with bST (Early et al., 1990b), and an increase in metacarpal bone diameter (dorsal-palmar) was observed in Quarter horse-type yearlings treated with somatotropin (Thomson et al., 2002). In agreement with Johnsson et al. (1985), bone density was not different among treatments in this study, but Carter and Cromwell (1998) demonstrated a decrease in metacarpal-metatarsal bone and femur strength with somatotropin administration in pigs.

Ossification of the long bones of cattle occurs after 18 to 24 mo of age (Sisson, 1917). Therefore, bST should have been able to stimulate long-bone growth throughout the study. This is supported by the fact that the bST-bST steers had the greatest hip height for the entire experiment. Skeletal growth, as measured by hip-height gain, decreased by two-thirds from the first phase of the study to the second, which is in agreement with the sigmoidal growth curve of meat animals in which bone matures first (Boggs and Merkel, 1993).

Carcass Measurements
In agreement with Preston et al. (1995) and Holzer et al. (2000), the current study found no effect of bST on HCW in steers, but other studies demonstrated an increase in HCW in steers (Moseley et al.,1992; Rumsey et al., 1996) and in bull calves (Holzer et al., 1999) with bST treatment. Dressing percent decreased in the current study and previous studies (Early et al., 1990a; Moseley et al., 1992; Holzer et al., 1999). The decrease in dressing percent was in part a result of an increase in noncarcass weight at final slaughter in the current study and also as observed by Early et al. (1990b) and Rumsey et al. (1996). Early et al. (1990b) attributed 75% of the increase in noncarcass weight to increased weight of the gastrointestinal tract, but this was not evident in the study of Rumsey et al. (1996) and was not measured in the current study.

Early et al. (1990a) theorized that by administering bST to younger, lighter-weight cattle, the carcass component could be increased to a greater extent than the noncarcass components. Carcass protein accretion and muscles were increased in the current study and other studies (Eisemann et al., 1989; Rumsey et al., 1996). However, in the current study, these increases did not result in an increase in HCW, but noncarcass weight increased to a greater extent than observed by Early et al. (1990a). Therefore, most of the weight gained as a result of bST treatment was in offal rather than retail product.

Carcass fat was reduced in steers treated with bST as evident in reduced backfat, KPH percentage, marbling score, and USDA quality grade. Previously, bST administration to cattle reduced backfat (Peters, 1986; Moseley et al., 1992; Preston et al., 1995), KPH, marbling score (Preston et al., 1995), and the percentage of carcass grading USDA Choice (Moseley et al., 1992; Preston et al., 1995), although Early et al. (1990b) did not observe a difference in backfat or Canadian carcass grade.

Somatotropin decreased lipid accretion to a greater extent during the latter phase of the study when lipid accumulation was the greatest. Even though bST decreases lipid accretion, it does not prevent it entirely. As fat decreased, red meat yield increased in the current study as evidenced by a reduction in yield grade. This agrees with Preston et al. (1995) in which bST reduced yield grade scores by 12.5%.

Carcass Value
On an economic basis, the goal of using bST is to produce greater quantities of red meat without sacrificing the quality of the product. Table 10 demonstrates the premiums and discounts using average treatment values based on an average grid pricing system (USDA Market News Service, 2004) including quality grade, yield grade, and HCW. All carcasses were within the acceptable HCW range (250 to 431 kg). Although C-bST and bST-bST carcasses had lower yield grades and therefore greater cutability, the added value of the increased lean did not compensate for the reduced quality grade, and would be valued at $59.30 less than C-C carcasses. Carcasses from bST-C steers were discounted for both quality grade and yield grade, and therefore had $70.36 lower carcass value than C-C carcasses. Some of the loss in carcass value could be offset by the lowered DMI and reduced feed cost, but animal handling charges (treatments every 2 weeks) and cost of the product would need to be accounted for as well.

	IMPLICATIONS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION IMPLICATIONS LITERATURE CITED

	Footnotes

 
¹ This study was funded in part by Lilly Research Laboratories, Greenfield, IN, and the Michigan Agricultural Experiment Station.

² The authors would like to thank B. Sharma for his laboratory assistance and expertise.

³ Trade or product names are mentioned for the convenience of the reader and do not imply endorsement over comparable products.

⁴ Present address: Veterinary Services Department, The Zoological Society of San Diego, CA 92112-0551.

⁵ Present address: Department of Animal Sciences, Auburn University, AL 36849-5415.

⁶ Corresponding author: rust{at}msu.edu

Received for publication November 4, 2004. Accepted for publication September 19, 2005.

	LITERATURE CITED

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION IMPLICATIONS LITERATURE CITED

 


Anderson, P. T., D. R. Hawkins, W. G. Bergen, and R. A. Merkel. 1988. A note on dry-matter intake and composition of gain of Simmental bulls and steers fed to the same weight or age. Anim. Prod. 47:493–496.

AOAC. 1984. Official Methods of Analysis. 14th ed. Assoc. Offic. Anal. Chem., Arlington, VA.

Boggs, D. L., and R. A. Merkel. 1993. Live Animal Carcass Evaluation and Selection Manual. 4th ed. Kendall Hunt Publ. Co., Dubuque, IA.

Bristow, A. F., R. P. Gooding, and R. E. Gaines-Das. 1990. The international reference reagent for insulin-like growth factor-I. J. Endocrinol. 125:191–197.[Abstract/Free Full Text]

Butler-Hogg, B. W., and I. D. Johnsson. 1987. Bovine growth hormone in lambs: Effects on carcass composition and tissue distribution in crossbred females. Anim. Prod. 44:117–124.

Carter, S. D., and G. L. Cromwell. 1998. Influence of porcine somatotropin on phosphorus requirement of finishing pigs: I. Performance and bone characteristics. J. Anim. Sci. 76:584–595.[Abstract/Free Full Text]

Coble, D. S., L. L. Wilson, J. P. Hitchcock, H. Varela-Alvarez, and M. J. Simpson. 1971. Sire, sex and laterality effects on bovine metacarpal and metatarsal character. Growth 35:65–77.[Medline]

Dalke, B. S., R. A. Roeder, T. R. Kasser, J. J. Veenhuizen, C. W. Hunt, D. D. Hinman, and G. T. Schelling. 1992. Dose-response effects on recombinant bovine somatotropin implants on feedlot performance in steers. J. Anim. Sci. 70:2130–2137.[Abstract]

Early, R. J., B. W. McBride, and R. O. Ball. 1990a. Growth and metabolism in somatotropin-treated steers: I. Growth, serum chemistry and carcass weights. J. Anim. Sci. 68:4134–4143.[Abstract]

Early, R. J., B. W. McBride, and R. O. Ball. 1990b. Growth and metabolism in somatotropin-treated steers: II. Carcass and non-carcass tissue components and chemical composition. J. Anim. Sci. 68:4144–4152.[Abstract]

Eisemann, J. H., A. C. Hammond, and T. S. Rumsey. 1989. Tissue protein synthesis and nucleic acid concentrations in steers treated with somatotropin. Br. J. Nutr. 62:657–671.[Medline]

Enright, W. J., J. F. Quirke, P. D. Gluckman, B. H. Breier, L. G. Kennedy, I. C. Hart, J. F. Roche, A. Coert, and P. Allen. 1990. Effects of long-term administration of pituitary-derived bovine growth hormone and estradiol on growth in steers. J. Anim. Sci. 68:2345–2356.[Abstract]

Gill, J. L. 1988. Standard errors for split-split-plot experiments with repeated measurements of animals. J. Anim. Breed. Genet. 105:329–336.

Hankins, O. G., and P. E. Howe. 1946. Estimation of the composition of beef carcasses and cuts. Tech. Bull. No. 926. USDA, Washington, DC.

Holzer, Z., Y. Aharoni, A. Brosh, A. Orlov, and F. Buonomo. 2000. The influence of recombinant bovine somatotropin on dietary energy level-related growth of Holstein-Friesian bull calves. J. Anim. Sci. 78:621–628.[Abstract/Free Full Text]

Holzer, Z., Y. Aharoni, A. Brosh, A. Orlov, J. J. Veenhuizen, and T. R. Kasser. 1999. The effects of long-term administration of recombinant bovine somatotropin (Posilac) and Synovex on performance, plasma hormone and amino acid concentration, and muscle and subcutaneous fat fatty acid composition in Holstein-Friesian bull calves. J. Anim. Sci. 77:1422–1430.[Abstract/Free Full Text]

Johnsson, I. D., I. C. Hart, and B. W. Butler-Hogg. 1985. The effects of exogenous bovine growth hormone and bromocriptine on growth, body development, fleece weight and plasma concentrations of growth hormone, insulin and prolactin in female lambs. Anim. Prod. 41:207–217.

Krick, B. J., R. D. Boyd, K. R. Roneker, D. H. Beermann, D. E. Bauman, D. A. Ross, and D. J. Meisinger. 1993. Porcine somatotropin affects the dietary lysine requirement and net lysine utilization for growing pigs. J. Nutr. 123:1913–1922.[Abstract/Free Full Text]

Loy, D. D., H. W. Harpster, and E. H. Cash. 1988. Rate, composition and efficiency of growth in feedlot steers reimplanted with growth stimulants. J. Anim. Sci. 66:2668–2677.[Abstract/Free Full Text]

McBride, B. W., and W. M. Moseley. 1991. Influence of exogenous somatotropin on the components of growth in ruminants. Pages 91–103 in Biotechnology for Control of Growth and Product Quality in Meat Production: Implications and Acceptability. P. van der Wal, G. M. Weber, and F. J. van der Wilt, ed. Pudoc, Wageningen, The Netherlands.

Moseley, W. M., J. P. Paulissen, M. C. Goodwin, G. R. Alaniz, and W. H. Clafin. 1992. Recombinant bovine somatotropin improves growth performance in finishing beef steers. J. Anim. Sci. 70:412–425.[Abstract]

Owens, F. N., D. R. Gill, D. S. Secrist, and S. W. Coleman. 1995. Review of some aspects of growth and development of feedlot cattle. J. Anim. Sci. 73:3152–3172.[Abstract]

Peters, J. P. 1986. Consequences of accelerated gain and growth hormone administration for lipid metabolism in growing beef steers. J. Nutr. 116:2490–2503.[Abstract/Free Full Text]

Preston, R. L., S. J. Bartle, T. R. Kasser, J. W. Day, J. J. Veenhuizen, and C. A. Baile. 1995. Comparative effectiveness of somatotropin and anabolic steroids in feedlot steers. J. Anim. Sci. 73:1038–1047.[Abstract]

Rathmacher, J. A., F. J. Bonilla, C. Coates, D. C. Beitz, A. Trenkle, and S. L. Nissen. 1997. Effect of bovine somatotropin and RevalorS^® on tissue deposition rates in steers. J. Anim. Sci. 75(Suppl. 1):56. (Abstr.)

Rumsey, T. S., T. H. Elsasser, S. Kahl, W. M. Moseley, and M. B. Solomon. 1996. Effects of Synovex-S^® and recombinant bovine growth hormone (Somavubove^®) on growth responses of steers: I. Performance and composition of gain. J. Anim. Sci. 74:2917–2928.[Abstract]

Sharma, B. K., M. J. VandeHaar, and N. K. Ames. 1994. Expression of insulin-like growth factor-I in cows at different stages of lactation and in late lactation cows treated with somatotropin. J. Dairy Sci. 77:2232–2241.[Abstract]

Sisson, S. 1917. The Anatomy of the Domestic Animals. 2nd ed. W. B. Saunders Co. Philadelphia, PA.

Thomson, K. L., G. D. Potter, K. J. Terrell, E. L. Morris, and K. J. Mathiason-Kochan. 2002. Cortical bone width in juvenile race horses treated with exogenous somatotropin. Prof. Anim. Sci. 18:184–189.[Abstract/Free Full Text]

USDA Market News Service. 2004. National weekly direct slaughter cattle—Premiums and discounts for the week of 1/12/2004. Available: http://www.ams.usda.gov/mnreports/lm_ct155.txt. Accessed Jan. 15, 2004.

Yung, M. C., M. J. VandeHaar, R. L. Fogwell, and B. K. Sharma. 1996. Effect of energy balance and somatotropin on insulin-like growth factor I in serum and on weight and progesterone of corpus luteum in heifers. J. Anim. Sci. 74:2239–2244.[Abstract]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Schlegel, M. L. Articles by Rust, S. R. Search for Related Content PubMed PubMed Citation Articles by Schlegel, M. L. Articles by Rust, S. R.