| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
ANIMAL GROWTH, PHYSIOLOGY, AND REPRODUCTION |
Department of Animal and Range Sciences, South Dakota State University, Brookings 57007
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
|---|
Key Words: Beef • Body Composition • Implants • Estradiol • Trenbolone Acetate
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
|---|
). Implanting can improve carcass leanness by up to 8% compared with nonimplanted controls at the same BW. In 1991, the option of using a single implant that contained both an estrogen (estradiol) and an androgen (trenbolone acetate, TBA) was made available to beef producers. The combination of estradiol and TBA increased ADG and feed efficiency more than either substance alone (Preston, 1999). Research has shown that administration of a combination implant too close to slaughter can decrease marbling scores (Kerth et al., 1996). Pritchard (2000) suggested that the decrease in quality grade might result from administering an improper implant strategy. Using implants that differed in their level of potency, Pritchard (2000) reported that carcasses developed marbling scores similar to nonimplanted contemporaries if a lower-potency implant was administered early in the finishing phase. The disparity between experimental outcomes among studies may lie in the timing as well as the potency of the implant. Understanding how implants affect marbling development would aid in the selection of more appropriate implant strategies. This study was conducted to quantify the growth of intramuscular fat relative to changes in body composition in steers fed high-energy diets and implanted at two different points in the finishing phase growth curve. |
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
|---|
Angus and Angus x Limousin cross spring-born steers (n = 186) were weaned and transported 545 km to the South Dakota State University (SDSU) Nutrition Unit, where they were individually tagged and processed in early November. Before initiating the study, steers were backgrounded for 47 d at a targeted gain of 1 kg/ d. Steers were ranked by weight and four outliers were removed. Fifteen steers that were closest to the mean weight of the group were selected and randomly assigned to one of three serial slaughter treatments. Steers selected for serial slaughter were fed in pens by treatment. To measure production variables, the remaining 167 steers were randomly assigned to one of three treatments with seven replicates per treatment: 1) control, no implant (NI); 2) early implant (EI) on d 1 (BW = 309 kg); or 3) delayed implant (DI) on d 57 (BW = 385 kg). The implant that was administered for implanted treatments was an estradiol–TBA implant containing 24 mg of estradiol and 120 mg of TBA (Revalor-S, Intervet, Millsboro, DE). The allotment system caused a similar distribution of BW in each pen. Steers were fed in paved outdoor pens measuring 7.6 x 7.6 m deep, with a 7.6-m fence-line feed bunk. Each pen contained seven or eight steers. Steers were fed once daily in the afternoon and had continual access to water. Steers were brought up to ad libitum intakes within 14 d. The finishing diet comprised (DM basis) 40% whole shelled corn, 40% high-moisture corn, 10% ground grass hay, and 10% supplement, which contained (on a DM basis) 12.9% ± 0.09 CP, 6.1% ± 0.12 ADF, 13.7% ± 0.36 NDF, and 3.2% ± 0.08 ash, and was 74.9% ± 0.72 DM. The estimated final dietary energy density was 2.06 Mcal/kg of NEm and 1.36 Mcal/kg of NEg. Cattle were weighed on trial on December 21, 2000, at which time implants were administered to EI steers. Steers (n = 5) assigned to the initial slaughter group were transported to the SDSU Meat Lab and processed.
Three calves were removed from the study with their BW contribution to the pen mean deleted from the onset of the experiment. The South Dakota State University Animal Care and Use Committee approved the care, handling, and sampling of animals used in this study.
Steers were weighed every 28 d to monitor weight gain and to schedule appropriate implant and slaughter dates. Steers averaged 385 kg on d 56. The following day (d 57), the DI treatment (Revalor-S, Intervet) was administered. On d 58, steers assigned to serial slaughter from the EI treatment (n = 5) and nonimplanted (n = 5) were transported to the SDSU Meat Lab for slaughter. When the average of all steers visually reached 1.00 cm of rib fat thickness, 30 steers (n = 10 from each treatment) were selected from near the mean BW of each treatment for slaughter over a 10-d period at the SDSU Meat Lab for compositional analysis. This began after 140 d on feed. Production data were calculated through 140 d to maintain the integrity of the experimental units (pens). The remaining steers (n = 134) were transported 75 km to a commercial packing plant. Carcass data collected included hot carcass weight (HCW), LM area, s.c. rib fat thickness (RF), and percentage of kidney, pelvic, and heart fat (KPH) depots (USDA, 1996). Estimates of bone maturity and marbling score (to the nearest tenth) were recorded by trained university personnel or an official USDA meat grader. For steers slaughtered at the South Dakota State University Meat Lab (n = 30) the KPH depot was removed by physical separation from each side of the chilled carcass and weighed to determine the actual percentage of KPH relative to carcass weight.
Carcass Composition
Following carcass data collection, the 9th-10th-11th rib section was removed from the right side of each carcass as outlined by Hankins and Howe (1946) on the steers (n = 30) slaughtered at the SDSU Meat Laboratory. Soft tissue was separated from bone and weights were obtained on each. The soft tissue was mixed and homogenized in a bowl chopper. Three samples weighing 100 g each were obtained and stored in polyethylene bags at –20°C. Chemical analysis of the soft tissue was conducted to determine the water, ether extract (fat), and N contents of the 9th-10th-11th rib section samples. Two 50-g samples were lyophilized to a constant weight (48 h). Water was calculated as the difference between the wet sample and lyophilized sample weight. The lyophilized samples were then combined and immersed in liquid N and subsequently powdered with a Waring commercial blender (Waring Products Division, New Hartford, CT). Samples (2 g) were wrapped in ashless filter paper and extracted with petroleum ether in a side arm Soxhlet (AOAC, 1990) to a constant weight (60 h) for ether extraction of lipid followed by drying at 60°C for 12 h. Crude fat was calculated as the difference between lyophilized and extracted sample weight. Crude protein was measured on extracted samples (1 to 1.5 g) by the macro-Kjeldahl method (AOAC, 1990). Ash content was determined on 1-g lyophilized samples held at 650°C for 12 h. Hankins and Howe (1946) equations for steers were used to predict composition of the carcass soft tissue from chemical composition of soft tissue from the 9th-10th-11th rib section and to predict the percentage of carcass fat, protein, moisture, and ash. Equations are as follows: carcass fat = 3.49 + 0.74 (9th-10th-11th rib fat content); carcass protein = 61.9 + 0.65 (9th-10th-11th fat protein content); (Hankins and Howe, 1946). Whole carcass values were calculated by equations outlined by Hankins and Howe (1946) and used for determination of fractional growth rates. Empty body weight (EBW) was calculated by the following equation of Old and Garrett (1987), where EBW = ([1.316 x HCW] + 32.237).
Longissimus Sample
On the carcasses (n = 30) that were slaughtered for body composition study, a 1-cm slice of the LM was removed from the posterior portion of the 12th-rib section from the right side of the carcass. All exterior fat and epimysial connective tissue was removed. The sample was then cut into 1 cm x 1 cm cubes and stored in plastic bags (Whirlpack, Nasco, Fort Atkinson, WI) at –20°C. Samples were homogenized in liquid N as outlined previously. Ether extraction of the LM samples was performed in triplicate to quantify percentage of intramuscular fat (IMF) content of the LM at the 12th rib as outlined previously with the 9th-10th-11th rib sample.
Fractional Growth
Fractional growth rate (FGR) was calculated as outlined by McCarthy et al. (1983) as the rate of carcass protein and fat gain divided by the total carcass protein or fat of the animal at the point of reference (d 0, 56, or 150). Growth rate is reported as a percentage increase in mass of growth per day. The equation to calculate FGR is as follows: FGR = ([P1 –P0]/T)/([P1+ P0]/2), where P1 is the later measure of carcass tissue, P0 is the earlier measure of carcass tissue, and T is the number of days between the two measurements.
Statistical Analyses
All performance variables were evaluated using GLM procedure of SAS (SAS Inst., Inc., Cary, NC) in a statistical model that included treatment in a one-way treatment design. The experimental unit in these analyses was pen. Fisher’s LSD was used to separate treatment means. Analysis of carcass data was conducted using a complete random design in a model that included the main effect, implant treatment. Carcass traits were regressed against empty BW and partitioned into comparisons for linear, quadratic, and cubic relationships based on contrasts for the model (Steel and Torrie, 1960). Regression equations were developed to quantify the change in carcass characteristics and composition throughout the feeding phase with P < 0.05 considered significant and P < 0.10 tending to be significant.
|
Results and Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
|---|
Feedlot performance data are summarized in Table 1. Implanting increased BW and ADG, which are similar to responses reported by others (Duckett et al., 1997). The estradiol–TBA implant (containing 24 mg of estradiol and 120 mg of trenbolone acetate) administered on d 0 (EI) increased (P = 0.002) BW by 3% and increased (P = 0.004) ADG 11% to d 56. During the period from d 57 to 112, implanted steers had 2% greater (P = 0.05) BW than NI. The responses reported here are lower than previously reported by Preston and Rains (1993) and Pritchard (2000), who reported a 20% increase in ADG, as well as by Johnson et al. (1996), who observed an 18% increase in ADG over 140 d. The authors (Preston and Rains, 1993; Johnson et al., 1996; Pritchard, 2000) reported that implanted steers maintained greater gains throughout the experiment than controls. In the present study, EI steers implanted had increased ADG up to d 56, but d 57 to d 112 and cumulative ADG (d 140) did not differ from controls or DI.
|
). These results are similar to those reported by Johnson et al. (1996) but in contrast to those of Bartle et al. (1992) and Pritchard (2000), who reported that estradiol–TBA implants stimulated DMI. In the present study the failure of the implant treatment to elicit a DMI response may have been caused by the high intake occurring during cold, winter weather.
Gain efficiency was improved (P = 0.003) 13% for EI vs. NI the first 56-d period. At the conclusion of the trial, steers receiving an implant (EI or DI) had 10.5% improvement (P = 0.002) in feed efficiency over controls. This response is similar to previously reported results of 13% (Johnson et al., 1996) and 14% (Pritchard, 2000). However, EI did not maintain the advantage in G:F over controls from d 56 to d 112, whereas others (Johnson et al., 1996; Pritchard, 2000) have reported an advantage throughout the duration of the trial (140 d for Johnson et al., 1996; 145 d for Pritchard, 2000).
Carcass Characteristics and Composition
Carcass measurements and carcass composition for the initial slaughter group are shown in Table 2. Serial slaughter at d 56 and the final slaughter on d 150 are presented in Table 3. During the first 56 d, HCW increased (P = 0.010) for EI vs. NI, with no differences observed for other carcass traits. Implanting increased (P = 0.010) carcass weights by improved (P = 0.011) dressing percent, as well as by increasing BW at final slaughter. Eversole et al. (1989) found no difference in dressing percent for steers receiving one estradiol–TBA implant, but reported an increase in dressing percent for steers that were reimplanted with estradiol–TBA. Others (Perry et al., 1991; Pritchard, 2000) have reported increases in HCW with no difference in dressing percent.
|
|
; Perry et al., 1991; Bartle et al., 1992; Pritchard, 2000). Implanting increased (P < 0.001) LM area on d 150, which is similar to reports by Eversole et al. (1989), Bartle et al. (1992), and Pritchard (2000). Longissimus muscle area measurements for EI steers at initial (d 0) and on d-56 slaughter dates were not different from controls. These findings are similar to results reported by Johnson et al. (1996), who noted no difference in LM area 40 d after implanting with estradiol–TBA acetate. No difference was observed for KPH fat in steers slaughtered at d 56 or d 150. Similarly, Milton et al. (2000) reported no difference for KPH fat in steers administered an estradiol–TBA implant (28 mg/200 mg) on d 0, 35, or 70 compared with nonimplanted controls. Others (Bartle et al., 1992; Johnson et al., 1996) reported that implanted steers had less KPH than nonimplanted steers. Yield grade did not differ among treatments at d 56, which is similar to serial slaughter findings of Johnson et al. (1996), who reported no difference in yield grade at 40, 115, and 143 d after implanting. However, at final slaughter DI had lower (P = 0.038) yield grade than NI, which is in contrast to the findings of Eversole et al. (1989) and Bartle et al. (1992), who reported no difference in yield grade between implanted and nonimplanted steers.
Early implant treatment decreased (P = 0.021) marbling scores compared with controls, with no difference (P = 0.36) between NI and DI at final slaughter. Likewise, EI caused a lower (P = 0.070) percentage of carcasses with marbling scores of greater than or equal to Modest00 (Table 4). Morgan (1997) stated that TBA-containing implants produced approximately 25% fewer carcasses grading Choice or higher, whereas Kerth et al. (1996) reported that a combined estradiol–TBA implant decreased marbling scores one full marbling score compared with nonimplanted controls. In the present study, we found that EI on d 0 decreased (P = 0.006) marbling scores compared with controls, whereas DI was similar to controls. Both Eversole et al. (1989) and Bartle et al. (1992) reported decreased marbling scores with administration of an estradiol–TBA implant on d 0 compared with controls. An objective measurement of IMF content was conducted by quantifying the percentage of IMF content of the longissimus dorsi at the 12th rib (n = 30). No differences for IMF were detected among treatments at 56 d or 150 d; however at 150 d, EI steers had a percentage of IMF that was 21% lower than controls (5.08 vs. 4.03).
|
). Whole carcass composition of steers serially slaughtered at d 56 and final slaughter are presented in Table 5. Implanting with an estradiol–TBA implant at d 0 or 56 had no effect on percentage of whole carcass protein, fat, moisture, or bone. Likewise, no differences among treatments were detected when proportions of protein and fat were evaluated on an EBW basis. These results are similar to results reported by Johnson et al. (1996), who found no difference in the percentage of carcass components throughout serial slaughters at d 40, 115, and 143.
|
. During the initial 56 d, steers receiving an implant on d 0 (EI) had greater FGR for protein compared with NI (NI 0.41 vs. EI 0.53; P = 0.021), with no difference in the FGR of carcass fat. Steers receiving an implant on d 57 had greater (P = 0.012) rates of protein accretion from d 57 to d 150 compared with steers receiving an implant on d 0. Fractional accretion rate of percentage of IMF during the first 56 d did not differ between NI and EI, but EI numerically reduced FGR by 43% compared with NI. Cumulative FGR for protein and fat were not different among treatments, but the FGR of IMF tended to be lower (P = 0.06) for EI compared with NI.
|
. Implanting on d 0 increased EBW (P = 0.01) the first 56 d on feed compared with NI. Likewise, EBW tended to increase (P = 0.06) for cattle receiving an implant (EI or DI) compared with NI at the conclusion of the study, with no difference in the percentage of protein or fat between treatments. Regression equations (Table 8) were developed by regressing kilograms of empty body fat (EBF), percentage of IMF, and marbling against EBW and were found to be linear. Steers receiving EI had lower (P = 0.031) rates of development of percentage of IMF compared with NI but were not different (P = 0.111) from DI (Figure 1).
|
|
|
). Empty body weights at a constant EBF, IMF, and marbling score are presented in Table 9. At 28% EBF, steers receiving an implant (EI or DI) were 5.7% heavier on average than controls. Steers implanted on d 0 (EI) had 15% greater EBW at constant IMF content of 4% than NI. Likewise EI had 7.3% greater EBW than NI at a marbling score of Small0.
|
nutrient requirements of beef cattle adjust cattle so they are equivalent in body composition to the steers in the Garrett (1980) database. In the equations (NRC, 1996), the standard reference weight at which cattle reach an expected final body fat was determined by averaging the percentage of body fat of cattle in studies where body composition was measured and many different body types and sizes were represented (Harpster, 1978; Danner et al., 1980; Lomas et al., 1982; Woody et al., 1983) and the reference points are reported as 27.8% EBF at a small degree of marbling, with an EBW of 478 kg. In our study, control steers reached 28% body fat at 546 kg, whereas EI and DI reached 28% body fat at 579 and 597 kg, respectively (Table 9). Cattle in this study reached marbling scores of Small0 at a lower percentage of body fat and had lower EBW at Small0 marbling than those summarized by Fox et al. (1992) and Tylutki et al. (1994). It has been well documented that growth-promoting implants increase frame size (Loy et al., 1988; Perry et al., 1991; Fox et al., 1992). Implanted steers in our study reached 28% EBF at EBW that were 33 and 51 kg greater than controls for EI and DI, respectively. Perry et al. (1991) reported that steers implanted with estradiol–TBA, when compared with nonimplanted steers, reached a Small degree of marbling at live weights that were from 25 to 45 kg heavier than controls. In our study, NI and DI steers reached Small0 at similar weights, whereas EI increased the live weight at which steers reached Small0 by 36 kg compared with controls (Table 9). |
Implications |
|---|
|
TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
|---|
|
Footnotes |
|---|
2 Correspondence: ASC 217 Box 2170 (phone: 605-688-5452; fax: 605-688-6170; e-mail: kelly_bruns{at}sdstate.edu).
Received for publication June 23, 2004. Accepted for publication September 23, 2004.
|
Literature Cited |
|---|
|
TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
|---|
This article has been cited by other articles:
|
|
 |
|
  W. A. Griffin, D. C. Adams, and R. N. Funston The Effect of Delaying Initial Feedlot Implant on Body Weight, Average Daily Gain, and Carcass Characteristics of Calf-Fed Steers Professional Animal Scientist, April 1, 2009; 25(2): 145 - 149. [Abstract] [PDF]
|
|
|
|
 |
|
 J. A. Boles, D. L. Boss, K. I. Neary, K. C. Davis, and M. W. Tess Growth implants reduced tenderness of steaks from steers and heifers with different genetic potentials for growth and marbling J Anim Sci, January 1, 2009; 87(1): 269 - 274. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. J. Winterholler, G. L. Parsons, D. K. Walker, M. J. Quinn, J. S. Drouillard, and B. J. Johnson Effect of feedlot management system on response to ractopamine-HCl in yearling steers J Anim Sci, September 1, 2008; 86(9): 2401 - 2414. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. J. McPhee, J. W. Oltjen, J. G. Fadel, D. Perry, and R. D. Sainz Development and evaluation of empirical equations to interconvert between twelfth-rib fat and kidney, pelvic, and heart fat respective fat weights and to predict initial conditions of fat deposition models for beef cattle J Anim Sci, August 1, 2008; 86(8): 1984 - 1995. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. R. Smith, S. K. Duckett, M. J. Azain, R. N. Sonon Jr., and T. D. Pringle The effect of anabolic implants on intramuscular lipid deposition in finished beef cattle J Anim Sci, February 1, 2007; 85(2): 430 - 440. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. J. McPhee, J. W. Oltjen, T. R. Famula, and R. D. Sainz Meta-analysis of factors affecting carcass characteristics of feedlot steers J Anim Sci, November 1, 2006; 84(11): 3143 - 3154. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
