| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
ANIMAL PRODUCTION |
* Department of Animal and Food Sciences, Texas Tech University, Lubbock 79409-2141; and
Elanco Animal Health, Greenfield, IN 46140
 |
Abstract |
|---|
 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
|---|
Key Words: ß-adrenergic receptor agonist • beef cattle • feed intake • performance • ractopamine
|
INTRODUCTION |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
|---|
; Bell et al., 1998). Ractopamine hydrochloride (RAC) is a phenethanolamine that increases protein accretion, improves growth performance, and decreases adipose tissue deposition in livestock (Smith, 1987; Watkins, 1990; Xiao et al., 1999). Although positive effects on performance have been observed, research with other ß-AA in cattle (Sillence et al., 1993) and with RAC in swine (Marchant-Forde et al., 2003) has implicated RAC in potential adverse effects on cardiac function.
Ractopamine hydrochloride was approved for use in beef cattle in 2004, but only limited research with RAC in beef cattle has been published. As a result, little data evaluating optimal dose and duration are available (Pritchard, 2005). In addition, the possible effects of RAC on behavioral and metabolic variables in beef cattle are virtually unknown.
Our research evaluated the effects of varying doses and durations of feeding RAC on growth performance and carcass characteristics of feedlot cattle and the effect of RAC on the rate of intake and acid-base status of finishing beef steers.
|
MATERIALS AND METHODS |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
|---|
Experiment 1
Cattle. Three hundred seventy-four steers were received (3 separate loads; Brangus, British, and British x Continental breeding; average arrival BW = 331 kg) at the Texas Tech University Burnett Center (New Deal, TX) during late May and early June 2004. During processing, cattle were individually weighed and uniquely identified with an ear tag; hide color was recorded for each animal. All cattle were vaccinated (s.c.) with a modified live-virus vaccine (Titanium 5, Agri-Labs, Des Moines, IA) and a clostridial bacterin-toxoid (Vision 7 with SPUR, Intervet, Millsboro, DE) and treated with moxidectin for parasite control (Cydectin, Fort Dodge Animal Health, Overland Park, KS). Cattle were initially fed a 65% concentrate diet for approximately 15 d, then switched to a 75% concentrate diet, implanted with Ralgro (36 mg of zeranol; Schering-Plough Animal Health, Union, NJ), and sorted into 1 of 25 soil-surfaced pens. Over the next 2 wk, cattle were adapted to a 90% concentrate diet. After approximately 75 d on feed, cattle were weighed individually and reimplanted with Revalor S (120 mg of trenbolone acetate and 24 mg of estradiol; Intervet).
Treatments.
Of the 374 steers originally received, 360 (BW = 545 kg) were used in Exp. 1. Steers were blocked by BW at reimplant (8 blocks of 45 steers each). Blocks were assigned to 9 contiguous pens of identical dimensions (2.9-m wide x 5.6-m deep; 2.4 m of linear bunk space), and cattle were assigned randomly to pens within BW blocks (5 steers/pen). Pens were assigned to 1 of 9 treatments arranged in a 3 x 3 factorial design by dose [0, 100, or 200 mg/d of RAC (Optaflexx, Elanco Animal Health, Greenfield, IN)] and by duration of RAC feeding (28, 35, or 42 d before the slaughter). Distribution of hide colors (P = 0.78) and original loads (P = 0.92) were evaluated by 
2 procedures and found not to differ among treatments.
To provide the dose of RAC, 3 diets were fed during the experimental period: 1) Control (CON; no RAC); 2) a RAC-containing diet designed to provide 100 mg of RAC/steer daily (RAC100); and 3) a RAC-containing diet designed to provide 200 mg of RAC/steer daily (RAC200). Ingredient composition and chemical analyses of the diets and supplements are provided in Table 1. As noted previously, the 3 diets were fed for 28, 35, or 42 d before slaughter to provide differences in the duration of RAC feeding. Concentrations of RAC in the premixes (Table 1) were based on an assumed DMI of 9.96 kg/steer (average pretrial DMI the week before RAC feeding began).
|
Diets were mixed for 2.5 min in a 1.27-m3-capacity paddle mixer (Marion Mixers Inc., Marion, IA) and delivered by a drag-chain conveyor to a Roto-Mix 84-8 mixer/delivery unit (Roto-Mix, Dodge City, KS). Mixing order throughout the RAC feeding period was CON, RAC100, and RAC200. All scales in the feed mill and load cells on the mixer/delivery unit were calibrated and certified for accuracy before RAC feeding began. Diets were mixed for approximately 3 min after transfer to the mixer/delivery unit and delivered to treatment pens via load cells and an indicator on the unit (readability of ± 0.454 kg).
Feed samples for each diet were collected daily from the feed bunks at the time of delivery, bagged in plastic sample bags, and stored frozen. Samples were shipped weekly to SDK Laboratories (Hutchinson, KS) for compositing and analysis for chemical components. Composite samples were subsequently transferred by SDK Laboratories to Woodson-Tenent Laboratories (Memphis, TN) for analysis of RAC and monensin (Rumensin, Elanco Animal Health) concentrations. A duplicate set of daily samples was collected for frozen storage in the Texas Tech University Ruminant Nutrition Laboratory, from which a weekly composite sample was prepared and analyzed for DM content (drying overnight at 100°C in a forced-air oven).
At the end of the experimental period for each block of cattle, feed bunks were cleaned, orts were weighed, and a sample was dried in a forced-air oven at 100°C for approximately 24 h to determine DM content. The corrected total DM delivered to each pen was determined by subtracting the DM content of the orts at the end of the period from the total quantity of DM delivered to the pen for the entire period (as-fed delivery of feed multiplied by percentage DM). The corrected total DM delivered was then divided by the number of animal days to determine the average DMI/steer.
To achieve the desired degree of finish at approximately the same BW and degree of finish (approximately 1.27 cm of 12th-rib backfat), blocks of cattle were begun on the dietary treatments at different times. Cattle in the 2 heaviest blocks (blocks 7 and 8) were begun on trial first, with cattle in blocks 5 and 6, blocks 3 and 4, and blocks 1 and 2 beginning on trial at 1-wk intervals thereafter. Within each block, cattle assigned to the 42-d RAC treatments were begun first, followed 1 and 2 wk later by the cattle in the 35-d and 28-d duration treatments, respectively. This procedure allowed all cattle in a BW block to be weighed individually on the morning of shipment to slaughter. Cattle were weighed in the morning before feeding on scheduled weigh days, and BW measurements were collected on individual animals without withholding feed or water. The individual-animal scale [C & S Single-Animal Squeeze Chute (Garden City, KS) set on 4 Rice Lake Weighing Systems (Rice Lake, WI) load cells] was calibrated with certified weights (453.59 kg, Texas Department of Agriculture) within 24 h of use. Beginning and ending BW measurements for each block of cattle were obtained from September 21 through November 23, 2004, depending on the block and treatment group (duration of feeding).
Carcass Evaluation. At the end of the assigned feeding period, each treatment and block combination was shipped to a USDA-inspected slaughter facility (Plainview, TX). Personnel from the West Texas A& M University Beef Carcass Research Center collected HCW, liver abscess score, LM area, marbling score, KPH, fat thickness, and USDA yield and quality grades.
Statistical Analyses. Pen performance and carcass data were analyzed as a randomized complete block using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). Pen was the experimental unit, block was a random effect, and the residual was used to test for treatment effects. Fixed effects included dose and duration of RAC and the dose x duration interaction. The proportion of cattle grading USDA Choice or greater was analyzed as a binomial proportion using the GLIM-MIX procedure of SAS. The model was the same as for performance data. For performance and carcass data, when the dose x duration interaction was not significant (P > 0.10), linear and quadratic orthogonal contrasts for the main effects of RAC dose and duration of feeding were evaluated for all response variables.
Experiment 2
Seventeen crossbred steers (British x Continental) housed in soil-surfaced pens at the Texas Tech University Burnett Center were weighed individually using the animal scale described for Exp. 1. As before, the scale was calibrated before each use. Twelve of the 17 steers were selected for use in the experiment (the heaviest and lightest steers were eliminated), stratified by BW, and assigned randomly to 1 of 2 treatments, beginning with the lightest animal and proceeding to the heaviest.
Two treatment diets were fed during the 30-d study: CON and RAC200 (0 or 200 mg/(steer·d), respectively, as described for Exp. 1). Approximately 14 d before the RAC feeding period began, steers were familiarized with the feeding procedures that would be used during the trial by weighing the feed on a platform scale with a 90-kg capacity and a 0.45-kg readability (Ohaus Corp., Pine Brook, NJ) into 189.3-L buckets that were placed in front of each pen. After the feed was weighed for all 12 steers, feed was delivered with a 5-min interval between pens. This staggered feeding approach allowed for individual pen measurements to be taken at timed intervals.
Baseline measurements for blood gases and urine pH were collected 6 d before the beginning of the trial, during which time all the animals were consuming the control diet. All 12 steers were weighed, and arterial blood was collected for blood gas analysis. Hair was removed from both ears using livestock clippers to allow for easy detection of and access to arteries in the ear. Arterial blood was collected from the auricularis caudalis artery using a 3-mL, heparinized arterial blood sampling syringe and needle set (Vital Signs Inc., Englewood, CO), as described by Nagy et al. (2002). Immediately after collection, blood was analyzed for blood gas (IRMA Blood Analysis System, Diametrics Medical Inc., St. Paul, MN). Urine was collected in 15-mL test tubes for determination of urine pH (Accumet Basic, Fisher Scientific International, Pittsburgh, PA). The 15-mL test tube was inserted into the opening of the sheath, which in some instances would immediately cause urination. When cattle did not urinate within 2 min, the test tube was attached to the steer’s sheath by using a rubber band to secure it to excess hair hanging from the sheath, and the steer was released from the squeeze chute and placed in an individual holding pen. Once the steer urinated into the test tube (typically within 30 min), it was brought back to the squeeze chute, and the tube was removed, after which the urine pH was measured.
Baseline measurements for rate of intake were obtained for each steer 4 d before the beginning of the trial. Feed bunks were cleaned before the morning feeding, and the feed delivered was weighed for each steer at 5-min intervals among the 12 steers. Feed remaining in the bunk was removed from the pen and weighed from each pen every 30 min for the first 2 h, every hour until 4 h, and every 2 h thereafter until 8 h after feeding. On the following day (24 h after feeding), orts were weighed for each pen, and DM analysis was conducted on the orts.
Ingredient composition for dietary treatments and the supplement, along with chemical composition data for the 2 diets are provided in Table 1
. Concentrations of RAC in the premixes were based on an assumed DMI of 10.06 kg/steer (average pretrial DMI the week before the beginning of the experiment). Diets were mixed in the Roto-Mix mixer/delivery unit, as described for Exp. 1, weighed on the Ohaus platform scale into 189.3-L buckets, and then delivered to the pen on the 5-min staggered feeding schedule described previously. Mixing order throughout the experimental period was CON followed by RAC200.
The 2 experimental diets were initially fed on April 12 (d 1). At this time, BW measurements for all 12 steers were collected. Rate of intake measurements were collected on d 8, 15, 22, and 29. Likewise, 24-h orts were weighed, individual BW measurements were taken, and arterial blood and urine samples were collected the following day (d 9, 16, 23, and 30). Measurements were taken in the morning before feeding. After BW measurement and blood and urine collection on d 30, cattle were shipped to a USDA-inspected slaughter facility (Plainview, TX). Personnel from the Texas Tech University Meat Science Laboratory obtained carcass data, as described for Exp. 1, excluding the liver score data. Feed samples were collected daily and composited weekly, and composite samples were analyzed by SDK Laboratories, as described for Exp. 1.
Statistical Analyses. Performance and carcass data for Exp. 2 were analyzed as a completely random design (treatment as the sole fixed effect) using the MIXED procedure of SAS, with animal as the experimental unit. To determine day-to-day variation in intake (feed delivery), absolute daily deviations in feed DM delivered were calculated and adjusted for the total quantity of feed delivered to each animal by using the following equation:
 |
where d2 was the feed delivery for the current day, and d1 was the feed delivery for the previous day. An adjusted deviation was calculated for the overall feeding period, the first 7 d, and the first 14 d. These adjusted deviations were analyzed as repeated measures using the MIXED procedure of SAS. Animal was the experimental unit, and fixed effects included day, treatment, and the day x treatment interaction. The subject of the repeated measures analysis was animal within treatment, and the analyses were conducted using multiple covariance structures (autoregressive, autoregressive with heterogeneous variance, compound symmetry, and compound symmetry with heterogeneous variance) to determine the most appropriate structure. The covariance structure that resulted in the smallest Akaike and Schwarz’s Bayesian criteria was considered the most desirable for analysis. Compound symmetry with heterogeneous variance was the most appropriate structure for the overall feeding period and 14-d adjusted deviations, whereas compound symmetry was optimal for the 7-d adjusted deviations.
For rate of intake, the percentage of total DM consumed was calculated for each collection time (0.5, 1 h, and so on) and fitted using the REG procedure of SAS, with a model in which the percentage of total DMI at each time was regressed on time after feeding and time squared. The resulting quadratic equations were then solved to determine the time required (hours) for steers to consume 25, 50, 75, and 100% of their total daily DMI. These intake values, along with blood gas data and urine pH were analyzed as described for the daily intake deviation data using repeated measures with the MIXED procedure of SAS. Baseline measurements for each of these data sets were included as covariates in the analyses. As before, the subject of the repeated measures analysis was animal within treatment, and the analyses were conducted using multiple covariance structures. Covariance structures chosen for each trait were as follows: 25 and 50% intake rates were autoregressive; blood gas data were autoregressive with heterogeneous variance, except for partial pressure of CO2 (compound symmetry) and K+ (compound symmetry with heterogeneous variance); the 75% intake rate was compound symmetry with heterogeneous variance; the 100% intake rate was compound symmetry; and urine pH was autoregressive with heterogeneous variance.
|
RESULTS AND DISCUSSION |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
|---|
No RAC dose x duration of feeding interactions (P > 0.10) were noted for performance data (Table 2). As RAC dose increased, there were linear increases (P 
0.01) in final BW (FBW), ADG, and G:F. These results agree with summary data presented by Schroeder et al. (2004b), who reported increased ADG by steers fed RAC. These authors further noted that ADG by steers fed RAC at 100, 200, and 300 mg/(steer·d) was increased by 17.1, 19.6, and 25.7%, respectively, and total BW gain over the RAC feeding period for each treatment was 7.1, 7.8, and 10.9 kg above controls. In addition, G:F for steers was increased by 13.6, 15.9, and 20.5% for the 3 treatments, respectively. Anderson et al. (1989) also reported improved ADG and G:F for beef cattle fed RAC.
|
, which showed that performance responses to RAC in pigs were greatest from d 6 to 22 and decreasing linearly thereafter, indicating that RAC increases growth rapidly at the onset of feeding until a plateau is reached. This plateau theory may further be explained by the phenomenon of desensitization of ß-AA receptors with chronic exposure to ß-AA (Moody et al., 2000; Johnson, 2004). In the current study, linear increases with duration of RAC feeding were noted for DMI (P = 0.01) and G:F (P < 0.01).
Because duration of RAC feeding is not applicable to the CON diet, data were also evaluated using linear and quadratic contrasts for duration at both the RAC100 and RAC200 dose levels, excluding values for the control diet. Results for ADG, DMI, and G:F are shown in Figure 1. For steers receiving the RAC100 diet, linear effects were detected for ADG (P = 0.02) and DMI (P < 0.01), with a tendency for a linear increase in G:F (P = 0.09). Conversely, for steers receiving the RAC200 diet, quadratic effects were detected for ADG (P = 0.01) and G:F (P = 0.01). The maximal benefit in ADG and G:F from feeding RAC was observed at 35 d for the RAC200 treatment, whereas the maximal benefit for the RAC100 treatment was reached at 42 d. These results further support the receptor desensitization theory, indicating that feeding RAC at a greater dose seemed to produce a diminishing return as duration increased beyond 28 d. Nonetheless, the linear effects associated with the RAC100 treatment suggested that performance traits continued to improve when receptors were exposed to a lower level of RAC, thereby producing improved performance traits for an extended duration of feeding.
|
. As with performance data, no RAC dose x duration of feeding interactions (P > 0.10) were detected. The HCW increased linearly (P = 0.02) as dose of RAC increased, whereas there was a tendency (P = 0.09) for HCW to respond quadratically relative to duration of feeding. These results agree with the summary data reported by Schroeder et al. (2004b), who noted increased HCW of 2.9, 6.4, and 8.3 kg for the 100, 200, and 300 mg/(steer·d) treatments, respectively. In the present data, there also was a tendency (P = 0.09) for a linear increase in LM area as RAC dose increased. No additional dose or duration differences (P 
0.14) were observed for other carcass characteristics, except for a tendency (P = 0.09) for a quadratic increase in percentage of carcasses grading USDA Choice or greater relative to duration of feeding. Our results for carcass characteristics differ from those in other trials, which showed increased yield grade, dressing percent, and LM area when RAC was fed to beef cattle (Anderson et al., 1989; Schroeder et al., 2004a).
|
0.20) between CON and RAC200 treatments, respectively. Likewise, there were no differences (P 0.43) in ADG (0.79 and 1.07 kg; SE = 0.24), DMI (8.78 and 9.39 kg/d; SE = 0.55), or G:F (0.09 and 0.10; SE = 0.02) for CON and RAC200 steers, respectively. Cattle performance is typically improved by feeding RAC (Anderson et al., 1989; Schroeder et al., 2004b); however, Johnson (2004) reported inconsistent results for live BW gain and ADG, ranging from a 9% decrease in ADG to a greater than 30% increase. Despite the lack of statistical significance in the current study, which likely reflects the small number of animals per treatment, changes in ADG and G:F in the RAC200 treatment group were consistent with effects noted in Exp. 1. With respect to carcass effects, RAC increased (P = 0.04) LM area by approximately 13% (94.6 vs. 108.7 cm2 for CON vs. RAC200; SE = 4.13) and decreased (P = 0.03) yield grade by 0.77 points (2.57 vs. 1.80 for CON vs. RAC200; SE = 0.22). There were no differences for other carcass traits (data not shown). Anderson et al. (1989) reported decreased yield grade for steers fed varying does of RAC, and Schroeder et al. (2004b) reported increased LM area for steers fed RAC.
Results for direct and calculated blood gas measurements are shown in Tables 4 and 5, respectively. There were no differences between treatments for any of the blood gas, electrolyte, or metabolite measurements (P > 0.10). There was a treatment x day interaction (P = 0.03) for the partial pressure of O2, as well as effect of day (P < 0.05) for the partial pressures of CO2 and O2, bicarbonate, base excess of extracellular fluid, and O2 saturation. Urine pH results are shown in Table 6. Similar to the blood data, there were no treatment effects (P = 0.39) for urine pH, but there was a day effect (P = 0.02). To our knowledge, there are no other data available comparing the acid-base status of cattle fed RAC diets. Based on blood gas, electrolyte, and metabolite concentrations, urine pH, and the fact that the DMI by cattle in Exp. 2 was comparable to that by cattle in Exp. 1, it seems likely that RAC has minimal effects on the acid-base balance of feedlot steers.
|
|
|
), expressed as the relative deviation did not differ between treatments over the entire experimental period (P = 0.75), the first 7 d (P = 0.86), or the first 14 d (P = 0.69). There was, however, a day effect (P < 0.01) for the entire feeding period, as well as for the first 14 d (P < 0.01). Although these day effects suggest that intake varied noticeably from day to day, there were 3 d for which abnormally large deviations were noted for both the RAC and the CON groups. These variations were associated with days on which rate of intake measurements were obtained or on days in which rainfall occurred.
|
; Schwartzkopf-Genswein et al., 2004). Moreover, cattle vary markedly in their ability to cope with dietary factors that might cause acidosis, even after adaptation to high-grain diets (Brown et al., 2000). Variation in an individual animal’s ability to adapt to adverse situations was shown by Brown et al. (2000), when only 2 of 5 steers on diets formulated to cause acute acidosis had to be removed from the study because of inappetence. Likewise, Schwartzkopf-Genswein et al. (2003) reported that cattle in both high and low ADG groups had similar, but noticeable variation in intake, indicating that day-to-day fluctuations in intake by individuals may not necessarily exert a negative effect on growth performance.
Rate of intake data are shown in Figure 3. There were no treatment differences for time required to consume 25% (P = 0.26) of the daily feed intake; however, it took less time for CON steers to consume 50% (P = 0.09) and 75% (P = 0.10) of their daily feed intake, with a tendency for CON cattle to consume 100% (P = 0.12) of their daily feed intake in less time than RAC cattle. These data indicate that feeding RAC changes the within-day intake pattern of feedlot steers. Nonetheless, based on performance, carcass, blood gas, and urine pH data in the current study, it seems that this change in intake pattern did not cause either adverse or favorable changes from a performance or metabolic standpoint. There are few reports in the literature evaluating the effects of different intake patterns or variation in feed intake on performance or metabolic changes in cattle. Thus, it is not possible to speculate what effect a slower rate of intake might have on feedlot cattle. Schwartzkopf-Genswein et al. (2003) alluded to the fact that the rate at which a particular animal consumes feed may affect its ability to maintain ruminal pH. Further research is needed to verify our results and to determine the effects of changes in rate of feed intake on feedlot cattle.
|
|
Footnotes |
|---|
2 Corresponding author: judson.vasconcelos{at}ttu.edu
Received for publication May 11, 2007. Accepted for publication June 18, 2007.
|
LITERATURE CITED |
|---|
|
TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
|---|
This article has been cited by other articles:
|
|
 |
|
  S. F. Holmer, D. M. Fernandez-Duenas, S. M. Scramlin, C. M. Souza, D. D. Boler, F. K. McKeith, J. Killefer, R. J. Delmore, J. L. Beckett, T. E. Lawrence, et al. The effect of zilpaterol hydrochloride on meat quality of calf-fed Holstein steers J Anim Sci, November 1, 2009; 87(11): 3730 - 3738. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. D. Etherton ASAS Centennial Paper: Animal growth and development research: Historical perspectives J Anim Sci, September 1, 2009; 87(9): 3060 - 3064. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. J. Vogel, G. C. Duff, J. Lehmkuhler, J. L. Beckett, J. S. Drouillard, A. L. Schroeder, W. J. Platter, M. T. Van Koevering, and S. B. Laudert Effect of Ractopamine Hydrochloride on Growth Performance and Carcass Traits in Calf-Fed and Yearling Holstein Steers Fed to Slaughter Professional Animal Scientist, February 1, 2009; 25(1): 26 - 32. [Abstract] [PDF]
|
|
|
|
|
|
W. A. Griffin, G. E. Erickson, B. D. Dicke, T. J. Klopfenstein, R. J. Cooper, D. J. Jordon, R. S. Swingle, W. M. Moseley, G. E. Sides, and D. J. Weigel Effects of Ractopamine (Optaflexx) Fed in Combination with Melengestrol Acetate on Feedlot Heifer Performance Professional Animal Scientist, February 1, 2009; 25(1): 33 - 40. [Abstract] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
