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ANIMAL GROWTH, PHYSIOLOGY, AND REPRODUCTION |
* Instituto de Ciencias Agrícolas, Universidad Autónoma de Baja California, Ejido Nuevo León, Baja California, México;
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Asociación Ganadera Local Especializada en Bovinos para Engorda de Baja California, Mexicali, Baja California, México;
and
Instituto de Investigaciones en Ciencias Veterinarias, Universidad Autónoma de Baja California, Mexicali, Baja California, México; and
and
Department of Animal Science, University of California, Davis 95616
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: ß-adrenergic receptor agonist • carcass characteristic • feedlot cattle • meat quality
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Crome et al., 1996). Mexico and South Africa approved use of ß-AA, including the feed additives zilpaterol hydrochloride (ZH) and ractopamine hydrochloride (RH), more than 10 yr ago to improve feedlot performance. In 2003, RH was approved for use in cattle in the United States, and ZH was just approved in 2006 for increased rate of weight gain, improved feed efficiency, and increased carcass leanness in cattle fed in confinement for slaughter during the last 20 to 40 d on feed. Use of all ß-AA is prohibited in Europe (Council of European Communities, 1986), and this is unlikely to change in the near future.
The ß-AA are organic molecules that bind to ß-adrenergic receptors, present on most mammalian cells, to increase skeletal muscle mass and protein content through hypertrophy and reduce fat accretion (Yang and McElligott, 1989). Although the mechanism of action of ß-AA is not fully understood, ß-AA administered orally to mammals may increase muscle protein synthesis or decrease muscle protein degradation, or both, as well as decrease carcass fat mass (Dunshea et al., 2005) because of decreased lipogenesis and increased lipolysis (Mersmann, 1998).
In Mexico, consumption of viscera from animals fed with clenbuterol has caused acute toxicity in consumers, indicating an abuse in the use of this product, and therefore this ß-AA was removed from the market. However, ß-AA such as ZH and RH are metabolized rapidly and cleared from cattle tissues (Sumano et al., 2002). Moreover, Mexican beef feedlot operators and meat packers need to know the potential advantages of using legal ß-AA products as well as their impact on carcass traits and meat quality.
Therefore, the objective of this study was to evaluate effects of ZH and RH on feedlot performance, carcass characteristics, and meat quality of beef steers.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Location of the Study
The study was completed at the Feedlot Experimental Unit of the Instituto de Investigaciones en Ciencias Veterinarias of the Universidad Autónoma de Baja California, located 10 km south of Mexicali in northwestern Mexico. The zone has a latitude of 32° 40' and a longitude of 115° 28', is about 10 m above sea level, and has Sonoran desert conditions. The experiment was conducted between February and March, with an average temperature of 18.6°C and relative humidity of 50.6%.
Animals, Housing, and Experimental Design
Forty-five crossbred steers (approximately 50% Charolais, 30% Limousine, and largely Zebú in the remainder) and 9 Brangus, with an average initial BW of 424 ± 26.6 kg, were used in a 33-d feeding study. This period is considered the last phase during the feedlot stage, so that steers had been previously adapted to the steam-rolled wheat grain-based finishing diet. In Mexico, beef consumers demand meat with low fat content, so cattle are killed at a lighter BW, and therefore they are in the feedlot for a shorter period of time. Steers were selected from 2 pens of 60 cattle each from a commercial feedlot and transported to the experimental unit.
Beginning 105 d before initiation of the study, all steers were managed similarly, including vaccinations (Express 5 HS and Caliber 7, Boehringer Ingelheim, Jalisco, México), injection of vitamins (4 mL of Se Ve, LAPISA, Michoacán, México), parasite control (injection of 10 mL of Novox 50, PISA, Jalisco, México), and implantation with a combination of 100 mg of progester-one and 10 mg of estradiol benzoate (Synovex-C, Fort Dodge Animal Health, Overland Park, KS). Sixty days before the study, the steers were treated again and reimplanted with a combination of 200 mg of trenbolone acetate and 28 mg of estradiol benzoate (Synovex Plus, Fort Dodge Animal Health) and given parasite control again [12 mL of Albendaphorte 10%, Salud y Bienestar Animal (Distrito Federal, México)]. The selected steers showed no symptoms of morbidity, were uniform in BW, and were blocked by initial BW and assigned to 18 pens, each containing 3 steers (i.e., 6 blocks). Pen dimensions were 50 m2, with 21 m2 of overhead shade, which was in an east-west orientation. Automatic water troughs, with float-activated water supplies, were located at the north end of each pen. The concrete feed bunk in each pen was 3.7 m long. Pens were situated in 2 adjacent lines, 8 pens on 1 side and 10 pens on the other. The Brangus steers were equally distributed across each of the 3 treatments.
Pens were assigned to 1 of 3 treatments: 1) control (no feed additive in the diet); 2) 60 mg of ZH (Zilmax, Intervet, México City, México) steer–1·d–1; or 3) 300 mg of RH (Optaflexx, Elanco Animal Health, Greenfield, IN) steer–1·d–1. The ZH and RH feed additives were mixed into the mineral supplement and added to the diet. There was only 1 diet used during the finishing phase, and it was prepared in a commercial feed mill and transported to the experimental feedlot unit every 4 to 5 d. Table 1 shows the ingredient and nutrient composition of the diet. All steers were fed the control diet for 1 wk before initiation of the study to allow for acclimation to the diet and to the facilities. So that all steers arrived at the abattoir at the same time, the ZH-treated steers began the study 3 d earlier than the RH group to allow for the legal preslaughter ZH withdrawal time. During the feedlot phase, steers were provided ad libitum access to their diet and water. The steers were monitored daily for health status, including symptoms of acidosis.
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Carcass Data Collection
Immediately after termination of the feeding phase, the steers were transported to a commercial abattoir (Rastro TIF 301; located 5 km south from the Feedlot Experimental Unit) for slaughter according to an approved technique (NOM-033-ZOO-1995: Humanitarian slaughter of domestic and wild animals in México). Carcass and hide weights were collected after removal of KPH. After the carcasses were chilled for 24 h at –4°C, 12th rib fat (cm), LM area (cm2), pH, and weight of each carcass were recorded. The difference between the chilled carcass weight and HCW was used to estimate storage loss (this variable was estimated at 24 h because that is the one time the packing plant commercializes the carcasses). Dressing percent was calculated using HCW divided by final BW and multiplying the result by 100 (Boggs and Merkel, 1993). All 52 carcasses from the experimental animals were then deboned, and lean, bone, and fat data were collected from each pen, so there was a small loss because of the storing time and the deboning process.
Meat Quality Data Collection
Two LM steaks (10-cm thick) from each carcass were removed between 12th and 13th rib interface, frozen immediately on dry ice, and shipped to the Meat Quality Laboratory of the IICV-UABC in Mexicali (Baja California, México), where they were frozen at –20°C, vacuum-packaged, and stored for subsequent meat quality trait analysis. One-half of the steaks from each animal was analyzed 5 d postmortem, and the remaining one-half at 14 d. Variables measured at these times included pH, color, shear force (SF), water-holding capacity (WHC), and drip loss (DL).
For pH analysis, a portable pH meter with a puncture electrode (Delta Track Inc., ISFET pH 101, Pleasanton, CA) was used. The color values L* (lightness), a* (redness), and b* (yellowness) were determined using a Minolta CM-2002 spectrophotometer (Minolta Camera Co., Ltd, Osaka, Japan), utilizing an integrated specular component (SCI), a D65 illuminator, and a 10° observer. The chroma (C*) and hue angle (h°) were estimated as C* = [(a*)2 + (b*)2]
, and h° = tan–1(b*/a*). The 10-cm-thick steaks previously obtained from the rib were thawed and stored for approximately 24 h at 4°C.
To obtain SF values, previously cooked steaks of 1.27-cm diam. were aged 24 h and then cut parallel to the muscle fiber orientation. The SF measurements (kg/cm2) were determined using a Lloyd Texturometer (Lloyd Instruments, Fareham, Hampshire, UK) equipped with Warner-Bratzler shear blades with a crosshead speed of 50 mm/min. Water-holding capacity was determined using a modified compression technique described by Owen et al. (1982), from the method termed press juice (Boakye and Mittal, 1993), in which 0.3 kg of a meat sample is positioned between 2 layers of filter paper and 2 plaques of acyclic Plexiglas, and compressed at a force of 5 N for 60 s using the Lloyd Texturometer. The WHC was estimated as juice lost divided by the initial sample mass. Drip loss was measured using the technique described by Honikel and Hamm (1994).
Statistical Analyses
Feedlot performance variables and carcass characteristics were analyzed using a randomized complete block design, blocking according to initial BW, and weighted to the number of steers in each pen because of the 2 missing steers. Treatment effects were tested using orthogonal contrasts that compared the control vs. the RH and ZH groups. Results are reported as least squares means and P values, using the GLM procedure (SAS Inst. Inc., Cary, NC). Meat quality variables measured over time (pH, L*, a*, b*, C*, h°, SF, WHC, and DL) were analyzed using a mixed model with a randomized complete block design, by using the REPEATED and RANDOM statements of the MIXED procedure (SAS Inst. Inc.).
For each meat quality variable analyzed, several variance-covariance structures were evaluated (i.e., unstructured, simple, compound symmetry, first order autoregressive, and first order heterogeneous autoregressive). Selection of the variance-covariance structure was based on Akaike’s Information Criterion and the Bayesian Information Criterion, with the variance-covariance structure that resulted in these 2 criteria being closest to zero being used (Littell et al., 1996). The simple variance-covariance structure had the best fit for WHC, L*, a*, b*, C*, and h°, whereas for pH and DL the first order heterogeneous autoregressive had the best fit. Finally, a first order autoregressive variance-covariance structure best fit SF.
The linear model for meat quality variables included effects of day, block, treatments, and the interaction of day x treatment. Pen within treatment was considered as a random effect. The same orthogonal contrasts were used. Least squares means and SE are reported, and significance was declared at the 5% level. A trend to a difference was accepted where 0.05 < P < 0.10.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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) was similar for all treated groups (P = 0.958 for control vs. ZH, and P = 0.723 for control vs. RH). However, final BW was greater for ZH (P < 0.001) and RH (P < 0.030) steers compared with control steers. Steers fed ZH and RH had 26 and 24% greater ADG vs. control steers (P < 0.001 for both comparisons), respectively. Steers fed RH consumed less (P < 0.031) DM than control steers, but DM intake of ZH steers did not differ (P = 0.374) from control steers. Addition of either ß agonist to the diet considerably improved (P < 0.001 for both comparisons) G:F.
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), with carcasses from ZH and RH steers being 7% (P < 0.001) and 5% (P = 0.002) heavier than carcasses from control steers. As a result, carcass yield was greater in ZH steers (P = 0.003) and RH steers (P = 0.018) than in control steers. The LM area was larger (P < 0.02) in ZH steers than in control steers, but that of RH steers did not differ (P = 0.13) from control steers. There was a trend (P = 0.06) for ZH steers to have less 12th rib fat than control steers, but the amount in RH steers did not differ (P = 0.49) from control steers. After carcasses were deboned, RH steers tended (P = 0.07) to produce more lean then control steers, whereas meat yield of ZH steers and control steers did not differ (P = 0.14). Bone yield was similar for control vs. ZH (P = 0.186), and control vs. RH (P = 0.367), as well as fat yield for control vs. ZH (P = 0.367), and control vs. RH (P = 0.736).
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). There was a treatment effect (P = 0.03) for h°, indicating that both ß-AA led to increased redness of the LM area compared with control steers. There was only a trend (P = 0.065) for b* in treatment RH to be greater than in control steers, whereas the ZH treatment did not differ (P = 0.632) from control steers. A day x treatment interaction occurred (P < 0.05) for pH, WHC, DL, L*, a*, and C* variables. The interaction for pH indicated that, in general, pH values decreased slowly from d 1 to 5 and then increased by d 14. However, all values were within the accepted normal range of pH; therefore, these changes are not large enough to suggest an alteration of meat pH. A similar situation was observed with variables DL, C*, and a*, suggesting that color was similar for all groups. The WHC tended to decrease from d 5 to 14 in control and RH groups, although WHC for ZH steers had an opposite effect with time (Figure 1A). Meat lightness (L*) was similar for all groups (P = 0.272) on d 1 and 14 and on d 5 control steers showed lower (P = 0.035) L* values than treated steers (Figure 1b).
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Schroeder, 2004; Dunshea et al., 2005). However, the effect of ß-AA for extended time during the end of the finishing period on feedlot cattle performance appears to diminish as the time of treatment increases. This observation is consistent with desensitization and downregulation of the ß-adrenergic receptor, thereby decreasing growth rate responses (Moloney et al., 1991). In an experiment that fed cimaterol to steers from wk 4 of age to slaughter, Chikhou et al. (1993a) found little beneficial effect on growth rate and the efficiency of gain compared with a shorter-term treatment. In contrast, using the recently US-approved ß-AA RH at the same dietary level as in the current study, Schroeder (2004) summarized results from 10 experiments completed in different regions of United States during the feedlot finishing phase and found that ADG, total BW gain, and the efficiency of gain were improved significantly by 26, 20, and 20.5%, respectively, compared with nonsupplemented controls. A slightly lower response in the same variables was observed in heifers treated with RH. However O’Neill (2001) reported an increase of 10.4% in ADG, and 15.1% in the efficiency of gain in steers consuming 6 mg/d of ZH, although these differences were not statistically significant. However, Plascencia et al. (1999) reported an improvement of 36 and 39% in ADG and G:F, respectively, of steers when the finishing diet was supplemented with 6 mg/kg of ZH. Using other animal models (i.e., pigs, lambs, and rats), the increase in ADG and the efficiency of gain has been considerably greater when animals supplemented with a ß-AA were compared with nonsupplemented controls.
An impressive response of almost 22 kg in HCW for the ZH group, and of 14 kg for the RH group, compared with control steers has not previously been reported. Schroeder (2004) reported an improvement in HCW of 8.3 kg in steers treated with RH, and Plascencia et al. (1999) reported 13 kg more in HCW in steers treated with ZH, both vs. steers with no ß-AA supplementation. Wheeler and Koohmaraie (1992) fed 3 ppm of the ß-AA L644–969 to steers for 6 wk and reported that, even though treated and control steers had similar BW and ADG, treated animals had heavier HCW, larger LM area and lower USDA yield grades. However, fat deposition in several organs was not affected by ß-AA supplementation. The authors attributed these results to induced muscle hypertrophy, which, in turn, was due to increased calpastatin activity in supplemented steers. Chikhou et al. (1993b) fed cimaterol in the diet for a longer period (i.e., 60 wk) in Friesian steers and observed that cimaterol increased lean meat accretion, reduced adipose tissue deposition, increased SF values, and diminished meat quality, leading to their conclusion that benefits were minimal in terms of carcass composition. Increased muscle mass in mammals is recognized as an important effect of ß-AA oral administration by increasing the synthesis of muscle protein, reducing the degradation of muscle protein, or a combination of both. This ß-AA induced muscle hypertrophy is accredited to an increased rate of muscle 
-actin synthesis as well as to the inhibitory activity of calpastatin (Smith et al., 1989; Yang and McElligott, 1989; Helferich et al., 1990). Apparently, these effects were more evident for the ZH group in the current study than the RH group due to the improvement in LM area and the tendency to reduce 12th rib fat.
According to Price and Schweigert (1987), the pH range that categorizes a meat as normal is between 5.4 and 5.8, and the pH values obtained in the current study from the 3 groups were close to the lower value of this range. This suggests that our ß-AA did not alter meat pH, which is consistent with results of experiments using other ß-AA. For example, Fiems et al. (1990) fed cimaterol to Charolais and double muscled Belgian white-blue bulls and concluded that the treatment did not change meat pH, color, or water holding capacity.
In the current study, both ß-AA increased the SF of meat, which has been a general result in studies using feedlot cattle supplemented with these ß-AA. Vestergaard et al. (1994) reported a dramatic increase in SF (2- to 3-fold greater) in meat from young bulls fed cimaterol, and these results were corroborated by the taste panel evaluation. Luño et al. (1999) assessed the quality of meat from steers fed clenbuterol and found that meat texture variable determined with a Warner-Bratzler shear blade were similar at d 1 postmortem, but at d 8 postmortem, all parameters were increased in meat from treated steers. Schroeder (2004) reported that RH increased the SF of meat from steers, but the sensory panel did not detect differences in juiciness or flavor of meat from treated- and control-steers. However, O’Neill (2001) found no differences in SF values for meat from steers treated, or not treated, with ZH, and concluded that this ß-AA did not cause tougher meat.
Boleman et al. (1997) suggested a categorization of meat tenderness based on Warner-Bratzler SF where an intermediate meat is classified in a range of 4.08 to 5.40 Kg and a tough meat is classified when SF is between 5.9 and 7.1 Kg. In contrast, Miller et al. (2001) classified an intermediate meat between 3.92 and 4.5 Kg and a tough one between 5.42 to 7.2 Kg. According to these 2 categorizations of meat tenderness, meat from steers fed both ß-AA in the current study was within acceptable or intermediate classification. Factors induced by ß-AA treatment, such as reduced protein degradation, probably decreased proteolytic activity, decreased collagen solubility, and changed the fiber component of the muscle, which are all considered responsible for reduced meat tenderness (Geesink et al., 1993; Vestergaard et al., 1994).
According to the meat color variables measured, a trend to redness in meat color was uniform in all groups. With time, meat also tended to become paler, even though there was more red pigment than yellow. Meat from all 3 treatment groups darkened with time, but the effect was more evident in the ZH group. In general, there is no strong evidence that color was affected by either ß-AA. A trend to paler meat has been reported in studies using ß-AA (Geesink et al., 1993; Vestergaard et al., 1994), probably due to reduced heme pigmentation and to a larger proportion of fast twitch glycolytic fibers (Beerman et al., 1987; Wheeler and Koohmaraie, 1992).
It is confirmed that dietary supplementation of ZH and RH improved feedlot performance of steers based on values of ADG and the efficiency of gain. Hot carcass weight and dressing were also increased by ß-AA supplementation. The LM area was improved by ZH but not by RH. Both ß-AA increased SF, suggesting tougher meat than in the nonsupplemented steers. However, meat obtained from ß-AA supplemented steers was classified as having intermediate toughness. In general, meat color was unaffected by ß-AA supplementation. The use of ß-AA may optimize steer performance without substantively compromising meat quality.
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Footnotes |
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2 The authors thank Orlando Platt-Lucero and Baraquiel Fimbres-Preciado for support during the study, from the commercial feedlots Ganadera Platt and Engorda La Casita, respectively, from Rastro TIF No. 301 in Mexicali, Baja California, México, and from L. Erasmus of the University of Pretoria in obtaining a key thesis reference.
3 Corresponding author: lar62{at}uabc.mx
Received for publication March 23, 2006. Accepted for publication July 22, 2006.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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