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ANIMAL PRODUCTION |
,2
* Clayton Livestock Research Center, New Mexico State University, Clayton 88415;
and
Panhandle Research and Extension Center, University of Nebraska, Scottsbluff 69361;
and
Oklahoma State University, Stillwater 74078;
and
Beef Carcass Research Center, West Texas A&M University, Canyon 79016;
and
# Intervet Inc., Millsboro, DE 19966; and
|| Department of Animal and Food Sciences, Texas Tech University, Lubbock 79409
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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0.78) were detected among treatments for ADG and G:F from the start of the study until the final 50 d on feed. Final BW was greater for the average of the 3 ZH-treated groups (P < 0.01) than for the 0-d group. Average daily gain was greater for ZH-treated vs. control cattle during the final 50 d on feed (P < 0.01) and for the entire feeding period (P < 0.01). No differences in DMI were noted for any periods of the experiment (P 0.42) for ZH-treated cattle vs. controls. No differences were noted for DMI among the ZH-treated groups for the final 50 d on feed (P = 0.81) or for the overall feeding period (P = 0.31). Feeding ZH for any length of time increased G:F (P < 0.01) for the final 50 d and overall compared with 0-d cattle. In addition, a linear increase with more days of ZH feeding was observed for G:F during the period that ZH was fed (P = 0.01), as well as for the overall feeding period (P = 0.01). The ZH-treated cattle had heavier HCW (P < 0.01), greater dressing percent (P < 0.01), reduced marbling scores (P < 0.01), less 12th-rib fat (P < 0.01), larger LM area (P < 0.01), less KPH (P = 0.01), and a lower USDA yield grade (P < 0.01) than the 0-d cattle, regardless of the duration of ZH feeding. Dressing percent increased linearly (P < 0.01) with increased duration of ZH feeding, whereas 12th-rib fat (P = 0.07), marbling scores (P < 0.01), and USDA calculated yield grade (P = 0.01) decreased linearly with increased duration of ZH feeding. Feeding ZH increased ADG and G:F and decreased overall carcass fatness. In addition, effects of ZH on measures of carcass fatness were enhanced by feeding the product for a greater length of time.
Key Words: β-adrenergic receptor agonist • cattle • feedlot • performance • zilpaterol hydrochloride
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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; Bell et al., 1998). Feeding β-AA typically increases ADG, accompanied by a slight decrease in DMI with an ensuing improvement in feed efficiency (Mersmann, 2002). In addition, feeding β-AA has increased skeletal muscle protein mass, which is often associated with a decrease in adipose tissue mass (Byrem et al., 1998; Mersmann, 1998, 2002).
Zilpaterol hydrochloride (ZH; Intervet, Millsboro, DE) is a synthetic β-AA approved for use in feedlot cattle in the United States. Previous studies have shown that ZH has marked effects on BW gain, G:F, and carcass characteristics of beef feedlot cattle (Plascencia et al., 1999; Avendaño-Reyes et al., 2006; Vasconcelos et al., 2008). Zilpaterol hydrochloride was recently approved in the United States (FDA, 2006), but it has been used in feedlot cattle production since the 1990s in Mexico and South Africa (Avendaño-Reyes et al., 2006). Thus, to date, limited data have been published relative to effects of ZH on performance and carcass traits of feedlot cattle in the United States (Vasconcelos et al., 2008). Moreover, no data have been reported from experiments conducted with large-scale conditions, which are typical of most US feedlots. The objective of the present study was to evaluate the effects of duration of ZH feeding on performance and carcass characteristics of feedlot cattle by pooling data from 4 experiments conducted under feedlot conditions.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Exp. 1 and 2
British and British x Continental beef steers [n = 4,770; initial BW = 340.7 kg (Exp. 1); BW = 333.4 kg (Exp. 2)] were used in 2 trials conducted at a research facility located at Cactus, Texas, during fall 2006. Treatments consisted of feeding ZH (8.33 mg/kg of dietary DM) for the last 0, 20, 30, or 40 d of the feeding period, followed by a 3-d withdrawal period before slaughter. A randomized block design with 4 treatments and 7 (Exp. 1) or 6 (Exp. 2) blocks per treatment was used. Each block consisted of 4 adjacent pens containing steers of similar origin and date of arrival. Treatments were assigned randomly to pens within blocks, and steers were assigned randomly to pens, resulting in 2,569 (28 pens; 76 to 100 steers/pen) and 2,201 steers (24 pens; 80 to 98 steers/pen) in Exp. 1 and 2, respectively. After randomization, steers were brought by pen within block to the processing barn, where they were 1) weighed individually (those with a BW that differed from the expected pen mean BW by more than 2 estimated SD were removed); 2) identified with a uniquely numbered ear tag; 3) vaccinated with Vista 5 SQ (Intervet Inc.); 4) treated for parasites with Ivomec Pour-On (Merial, Duluth, GA) and Safe-Guard Oral Suspension (Intervet Inc.); and 5) implanted with Revalor-IS (80 mg trenbolone acetate + 16 mg estradiol; Intervet Inc.). Steers were reimplanted with Revalor-IS an average of 97 (range = 91 to 102; Exp. 1) and 73 (range = 67 to 81; Exp. 2) d before slaughter.
To establish their initial (d 0) BW, pens were group-weighed (2 or 3 drafts per pen) using platform scales (readability ± 45.4 kg) before feeding on the morning after each block was processed. For d-0 BW, actual scale BW data were used without adjustment (e.g., no shrink was applied). In Exp. 1 and 2, the mean days on feed across blocks were 170 and 164, respectively. Pen BW data 50 d before and on the day of slaughter were multiplied by 0.96 to adjust for gastrointestinal fill (NRC, 1996).
Feed was delivered 3 times daily during the transition period (22 d) and twice daily for the remainder of the study by means of a truck equipped with a mixer box mounted on load weigh cells. Delivered amounts were recorded electronically at each feeding, and feed records were maintained on a computerized system. Diet samples were obtained directly from the feed bunks during the morning feeding cycle. One portion of each sample was dried in a forced-air oven at 100°C to determine the DM percent, and a portion was retained and stored frozen. Samples were composited monthly and submitted to commercial laboratories for analysis of nutrient composition (Servi-Tech Laboratories, Amarillo, TX), as well as monensin (Eurofins Laboratory, Memphis, TN) and ZH concentrations (Intervet Analytical Laboratory, Lawrence, KS). The composition of the finishing diet was the same for Exp. 1 and 2 (Table 1). To reflect the widespread use of monensin and tylosin (Rumensin and Tylan, respectively; Elanco Animal Health, Indianapolis, IN) in feedlot diets, the control diet contained monensin and tylosin throughout the experiment. During the 3-d ZH withdrawal period before slaughter, all cattle were fed the control diet, which contained monensin and tylosin.
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). Exp. 3
Yearling beef steers (n = 2,067; British and British crosses) with approximately 85 steers per pen (84 to 91; initial BW = 426.4 kg) were used in an experiment that was conducted in a commercial feedlot in Parma, ID [(same 4 treatments described for Exp. 1 and 2); 6 blocks; 24 pens]. On arrival, cattle were individually identified and weighed and breed types were recorded, after which the cattle were assigned to blocks based on BW, breed type, and origin. Steers were vaccinated with Vista 5 SQ and Vision 7 (Intervet Inc.); treated for parasites with Cydectin (Fort Dodge Anim. Health, Overland Park, KS) and fenbendazole (Safe-Guard); and implanted with Revalor-S (24 mg of estradiol + 120 mg of trenbolone acetate; Intervet Inc.). Steers were not reimplanted. Diet and supplement samples were collected weekly and submitted to commercial laboratories for analysis of nutrient composition (SDK Laboratories, Hutchinson, KS) and ZH concentration (Intervet Analytical Laboratory). Composition of the finishing diet fed in Exp. 3 is shown in Table 1
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Cattle were fed twice daily. Pen BW (not shrunk) were obtained at the beginning of the experiment, and cattle were weighed again approximately 7 d before incorporating ZH into the diet (d -50). As in Exp. 1 and 2, during the 3-d withdrawal period cattle were fed the control diet, which contained monensin and tylosin. A final pen BW (multiplied by 0.96) was obtained on the day cattle were shipped to slaughter. Cattle were fed for an average of 136 d (from October 2006 to February 2007) and then slaughtered at a commercial facility (AB Foods, Toppenish, WA), where carcass data were collected as described for Exp. 1 and 2).
Exp. 4
Beef steers (primarily British crosses; n = 1,810; BW = 284 kg) were used in a trial conducted in a commercial feedlot in Watonga, OK. Steers within an arrival date were assigned randomly, 10 at a time, to 1 of 4 treatment pens in a block (same 4 treatments as in Exp. 1, 2, and 3). Immediately after randomization, steers were taken by pen to a platform scale and weighed in 1 draft; this BW served as the initial starting BW (not shrunk) for each pen. Initial processing of steers occurred after the initial BW was obtained and included vaccination with Vista 5 SQ and Vision 7; treatment for parasites with Ivomec Pour-On (Merial) and Safe-Guard (Intervet Inc.); metaphylactic treatment for bovine respiratory disease (Micotil, Elanco Animal Health); and implanting with Revalor-IS (Intervet Inc.). Steers were reimplanted with Revalor-S an average of 136 d before slaughter.
Cattle were fed 3 times daily. Steers were initially adjusted to a 95% concentrate diet using a series of 3 diets. Feed amounts delivered to each pen were recorded manually by the feed truck driver and electronically by the feed truck scale system. Diets were sampled daily for DM determination. Samples were dried in a forced-air oven at 110°C, and diet samples were sent to a commercial laboratory for analyses of nutrient composition, monensin, and ZH concentrations as described for Exp. 1 and 2. Composition of the finishing diet fed in Exp. 4 is shown in Table 1. As in the other experiments, during the 3-d ZH withdrawal period before slaughter, cattle were fed the control diet, which contained monensin and tylosin throughout the experiment.
Days on feed averaged 204 d. Each pen was weighed on a platform scale in 2 drafts (35 to 45 steers/draft) for determination of final BW (multiplied by 0.96 as in the other 3 experiments). The d -50 BW measurement was not collected in this experiment. Steers were shipped and slaughtered at a commercial slaughter facility (National Beef, Liberal, KS) during April 2007. Carcass data (same as in Exp. 1, 2, and 3) were collected at the time of slaughter by USDA meat graders, an independent carcass collection service (Cattle Trail Inc., Johnson, KS), and Oklahoma State University (Stillwater).
Statistical Analyses
Trial x treatment interactions were tested initially using the GLM procedures (SAS Institute Inc., Cary, NC). Significant trial x treatment interactions were noted for various ADG and G:F measurements. Subsequent evaluation of simple-main effects for treatments across trials demonstrated strong differences (P < 0.001) for all statistics of interest, with significant trial x treatment interactions. These responses, coupled with visual appraisal of response surface data, indicated that the interactions were primarily a result of magnitude differences for individual treatments across trials. Therefore, trial performance and carcass data were pooled and analyzed as a randomized complete block design using the MIXED procedure of SAS. Pen was the experimental unit for all analyses. The model statement included treatment, and the random statement included trial, block nested in trial, and the trial x treatment interaction. Nonparametric data (e.g., proportions of cattle in a particular USDA quality grade category) were analyzed as binomial proportions using the GLIMMIX procedure of SAS with the same overall mixed model described above. The binomial proportion approach that we used effectively treated a multinomial distribution (e.g., multiple categories of quality grades) as a series of individual binomial proportions. Thus, readers are cautioned that the P-values shown in the tables should not be interpreted as relating to the probability of differences in the distribution of various categories for a particular variable. Preplanned contrasts were used to test 1) the pairwise comparison of 0 vs. 20 d of ZH feeding; 2) 0 vs. the average of 20, 30, and 40 d of ZH feeding; 3) the linear effects of days fed ZH; and 4) the quadratic effect of days fed ZH. The 0- vs. 20-d comparison was included as a contrast to evaluate the effects of the response to 20 d, which is the ZH feeding period currently recommended by Intervet Inc. Results were considered significant if P < 0.05, with tendencies identified when the significance was between 0.05 and 0.10. For all statistics of interest, model assumptions were tested to ensure that variance components were analyzed appropriately. Model additivity was tested by outputting the predicted residual (pred) values, treating all variance components as fixed effects, adding the pred x pred effect to the model statement in PROC MIXED, and testing this effect for significance. For nonadditive models (P < 0.15) the appropriate transformation (e.g., log-transformation, power function, etc.) was used to ensure additivity before analysis with the original statistical model. Heteroscedasticity was tested with a null model likelihood ratio test by treating all variance components as fixed effects and identifying trial x treatment with the Repeated/Group option of PROC MIXED. For cases of heteroscedasticity (P < 0.15), the largest SE value is reported. The UNIVARIATE procedure was used to test normality of model residuals using a Shapiro-Wilks test. In cases of nonnormal distributions (P < 0.15), the data were rank transformed, analyzed by the same model as for nontransformed data, and compared against the original data to determine the most conservative probability values.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Performance data are presented in Table 2. No differences were detected for ADG, DMI, and G:F for the time period between initial BW to the final 50 d on feed (P 0.42). Final BW was greater for the average of the 3 ZH-treated groups (P < 0.01) than for the 0-d group. As would be expected from changes in BW, ADG differed between the 0-d group and the average of the 20-, 30-, and 40-d ZH groups, and was greater for ZH-treated cattle during the period in which treatment diets were imposed (P < 0.01) and for the entire experimental period (P < 0.01). Comparing cattle fed ZH with controls, no differences in DMI were noted from d 50 to the end of the study or for the overall feeding period (P 0.63). Moreover, no linear or quadratic responses were observed for DMI among the ZH-treated groups for the final 50 d on feed (P 0.30) or for the overall feeding period (P 0.31). Surprisingly, DMI for the time period between initial BW to the final 50 d on feed tended to decrease in a linear manner (P = 0.07) among the 3 ZH-treated groups during the time before ZH was fed, presumably reflecting random variation in DMI. With increased ADG and similar DMI, feeding ZH for any length of time increased G:F compared with the 0-d cattle (P < 0.01) for the final 50 d and for the overall feeding period. In addition, there was a linear increase in G:F with increasing days of ZH feeding during the period ZH was fed (P = 0.01), as well as during the overall feeding period (P = 0.01).
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in an experiment conducted with the same ZH treatments (ZH was fed for 0, 20, 30, or 40 d before slaughter plus a 3-d withdrawal period) and a randomized block design in a research setting with only 5 animals per pen. Vasconcelos et al. (2008) observed only a tendency (P = 0.15) for heavier final BW for ZH-fed cattle vs. 0-d cattle, and these authors reported a linear decrease in DMI during the period in which ZH was supplemented (20, 30, or 40 d), which was not observed in the pooled results from the present studies. In the results submitted for FDA approval of ZH (FDA, 2006), feeding ZH decreased DMI, but effects of length of the ZH feeding period on changes in DMI were not reported. Thus, it remains to be determined whether the length of time cattle are fed ZH has consistent effects on DMI.
As noted in the present study, Vasconcelos et al. (2008) also observed that ADG increased linearly during the ZH supplementation period, resulting in a linear increase in G:F as duration of ZH feeding increased. Plascencia et al. (1999) fed ZH to crossbreed yearlings steers (BW = 373 kg) in a 42-d finishing trial and did not observe effects of ZH on DMI; however, as in the present experiments, supplemental ZH increased ADG and G:F (Plascencia et al., 1999). Avendaño-Reyes et al. (2006) compared the effects of 2 β-AA [ZH and ractopamine hydrochloride (RH)] using 54 steers (BW = 424 kg) in a 33-d feeding study, and observed that steers fed ZH and RH had 26 and 24% greater ADG than control steers, respectively. Addition of either β-AA to the diet considerably improved G:F (Avendaño-Reyes et al., 2006). Steers supplemented with RH consumed less DM than control steers, whereas DMI was slightly less by ZH-treated cattle compared with controls, but the difference was not significant (Avendaño-Reyes et al., 2006).
Liver Abscesses
The percentage of livers with abscesses was greater for ZH-fed steers than for 0-d steers (P = 0.01; Table 3). This difference in occurrence of liver abscesses was somewhat expected because of the exclusion of tylosin from the diet during the time that ZH was fed. At the time these experiments were conducted, the combination of ZH, monensin, and tylosin was not approved by the US Food and Drug Administration; however, the combination approval was granted in 2008 (US Food and Drug Administration, 2008). Evaluation of data from the experiment of Vasconcelos et al. (2008), which also was conducted before the combination approval, indicated that the ZH groups had a numerical increase in the frequency of liver abscessed livers compared with the 0-d group. Nonetheless, because there were fewer animals in their small-pen study and relatively few cattle with abscessed livers, Vasconcelos et al. (2008) did not detect statistical differences among treatments for proportions of cattle with liver abscesses.
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Regardless of the duration of ZH feeding, cattle supplemented with ZH had a heavier HCW (P < 0.01), an increased dressing percent (P < 0.01), a reduced marbling score (P < 0.01), less 12th-rib fat (P < 0.01), a larger LM area (P < 0.01), less KPH (P = 0.01), and a reduced yield grade (P < 0.01) than the 0-d cattle (Table 3). Linear responses for duration of ZH feeding were observed for dressing percent (P < 0.01), marbling scores (P < 0.01), fat thickness (P = 0.07), and USDA calculated yield grade (P < 0.01). Dressing percent increased linearly (P < 0.01) with increased duration of ZH feeding, whereas 12th-rib fat (P = 0.07), marbling scores (P < 0.01), and USDA calculated yield grade (P= 0.01) decreased linearly with increased duration of ZH feeding. Skeletal and overall maturity scores decreased linearly with increasing days on ZH (P = 0.01).
Increased HCW, dressing percent, and LM area have been a consistent effect of ZH in carcasses of feedlot cattle (Plascencia et al., 1999; Avendaño-Reyes et al., 2006; Vasconcelos et al., 2008). Similar to present results, Vasconcelos et al. (2008) noted decreased 12th-rib fat and KPH for ZH-treated cattle compared with 0-d cattle, which reflects the nutrient repartitioning effects of ZH on lean and fat tissue depots. Consequently, ZH increases meat yield and dressing percent. Likewise, Avendaño-Reyes et al. (2006) observed that feeding ZH increased HCW, and that carcass leanness tended to increase when ZH was fed, whereas carcass fat was decreased by approximately 1 percentage unit, although this difference was not significant.
In the present study, the 0-d group had greater marbling scores than cattle fed diets containing ZH (P < 0.01), with a linear decrease in marbling score (P < 0.01) as duration of ZH feeding increased (Table 3). The comparison between 0- and 20-d of ZH feeding also showed a decrease in marbling scores when cattle were supplemented with ZH (P < 0.01).
Data for percentage of carcasses qualifying for USDA quality grades of Prime, Choice, Select, and Standard are shown in Table 4. The percentage of carcasses grading USDA Prime and Premium Choice was less (P < 0.01) for cattle fed ZH than for the 0-d cattle, was less (P < 0.01) when ZH was fed for 20 vs. 0 d, and decreased linearly with increased duration of ZH feeding (P < 0.01). Likewise, the percentage of cattle grading USDA Choice was less for ZH-treated cattle than for 0-d cattle (P = 0.01). The comparison between 0- and 20-d cattle, however, showed no differences in the percentage of cattle grading USDA Choice (P = 0.18). The percentage of cattle grading USDA Select was greater (P < 0.01) for 0 vs. 20 d of ZH feeding, and it increased linearly (P < 0.01) as duration of ZH feeding increased. In addition, a tendency for a quadratic response to the duration of ZH feeding was observed for the percentage of carcasses grading USDA Select (P = 0.06). No differences were observed between the 0-d group and the 3 ZH-treated groups for the percentage of carcasses grading USDA Standard (P = 0.51).
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. The smaller percentage (P 
0.01) of carcasses in categories with greater marbling scores [Small (P = 0.01); Modest (P < 0.01); and Moderate (P = 0.01)] was evident for cattle fed ZH vs. control cattle. The percentage of carcasses with Slightly Abundant marbling, however, did not differ (P = 0.49) between cattle fed ZH for any duration of time and 0-d cattle. In addition, only tendencies for differences were observed for Traces (P = 0.10), Modest (P = 0.11), or Moderate (P = 0.10) marbling scores for 20- vs. 0-d cattle. The percentage of Slight marbling scores was greater for carcasses in the 20-d ZH group compared with carcasses in the 0-d treatment (P < 0.01). As with the overall 0-d vs. ZH-feeding comparison, the percentage of Slightly Abundant marbling scores did not differ (P = 0.93) for carcasses of cattle fed ZH for 20 vs. 0 d.
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. No differences between the 0-d group and the 3 ZH-treated groups were observed for percentage of carcasses with yield grade 2.5 to 3 (P = 0.12) or 3 to 3.5 (P = 0.25); however, ZH-treated groups had a greater percentage of carcasses with yield grades <2 (P < 0.01) and with yield grades between 2 and <2.5 (P < 0.01). Results for the average of the 3 ZH feeding durations were similar to those for the comparison between 0 and 20 d of ZH feeding. In addition, the percentage of carcasses with yield grades between 3.5 and <4 (P < 0.01) and yield grades >4 (P < 0.01) was less for cattle fed ZH. In contrast, Vasconcelos et al. (2008), found no differences between the 0-d group and the 3 ZH-treated groups for these yield grade classes. Overall, however, the findings of the present study with respect to yield grade are generally consistent with data reported by Vasconcelos et al. (2008). Differences with duration of ZH feeding were observed for percentage of carcasses with yield grades <2 (P = 0.02; linear increase with greater duration of ZH feeding); yield grades 3.5 to <4 (P = 0.08; tendency for a linear decrease); and yield grades >4 (P = 0.07; tendency for a linear decrease).
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). Overall, the percentage of carcasses in HCW groups >431 kg was increased when ZH was fed (P 0.01). Percentage of carcasses in HCW groups >431 kg also was increased when ZH was fed for 20 vs. 0 d (P 0.02). Vasconcelos et al. (2008) found no differences among treatments (ZH feeding vs. controls) in the percentages of HCW when categorized as in the present study, although these authors noted that small sample sizes in the various subclasses might have limited their ability to detect differences, and differences among treatments followed trends similar to those observed in the present study.
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). The percentage of carcasses with LM area >103 cm2 increased linearly (P = 0.01) as duration of ZH feeding increased. In addition, a tendency (P = 0.08) for a quadratic response was observed in the percentage of LM areas between 77 and <90 cm2. Overall, these results are consistent with the findings of Vasconcelos et al. (2008), who noted a significant increase in the percentage of LM area >90 cm2 when ZH was fed and that the percentage of carcasses with LM area >103 cm2 tended to increase linearly as duration of ZH feeding increased.
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, who reported that DMI was decreased in a linear manner as duration of ZH feeding increased from 20 to 40 d.
In the present study, ZH increased HCW, dressing percent, and LM area, and it decreased 12th-rib fat, yield grade, and marbling scores. Although the average marbling score was less for cattle fed ZH for 20 d vs. 0-d cattle (420.0 vs. 434.3, respectively), percentage of carcass marbling scores (% of carcasses with Traces, Small, Modest, Moderate, and Slightly Abundant scores) did not differ (P 0.10) between cattle fed ZH for 20 vs. 0 d. Overall, the present results suggest that feeding ZH increased ADG, G:F, and decreased overall carcass fatness of feedlot cattle, and that feeding ZH for 20 d seems to provide the bulk of the benefits in terms of increased carcass weight and yield, while decreasing the negative effects of ZH on marbling scores and quality grades.
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Footnotes |
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2 Corresponding author: jvasconcelos2{at}unl.edu
Received for publication October 14, 2008. Accepted for publication February 18, 2009.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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