J. Anim. Sci. 2004. 82:2087-2091
© 2004 American Society of Animal Science
Effects of barley variety fed to steers on carcass characteristics and color of meat
J. A. Boles1,
J. G. Bowman,
L. M. M. Surber and
D. L. Boss
Animal and Range Sciences Department, Montana State University, Bozeman 59717-2900
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Abstract
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This study evaluated the effect of barley varieties in the diets of finishing steers on carcass composition, fat, and lean color and the fatty acid profile of subcutaneous fat. Crossbred steers (391 kg initial BW) were assigned randomly to one of five finishing diets composed primarily of corn (n = 9), Morex barley (n = 9), Steptoe barley, (n = 9), or two experimental barley varieties SM3 (n = 9) and SM5 (n = 9). Grains were cracked prior to feeding. Diets were formulated (DM basis) to be isonitrogenous (2.24% N) and isocaloric (2.01 Mcal/kg NEm and 1.35 Mcal/kg NEg). Steers were slaughtered according to industry-accepted procedures when it was visually estimated that 70% of carcasses would grade USDA Choice. After a 24-h chill at 4°C, carcass quality and yield grade data were collected by trained, experienced university personnel. Objective color (L*, a*, and b*) of both the LM and subcutaneous fat were measured, and samples of subcutaneous fat were removed from the 10th- to 12th-rib region for fatty acid analysis. Diet did not affect hot carcass weight (P = 0.15), fat thickness (P = 0.58), LM area (P = 0.57), percentage of internal fat (P = 0.52), yield grade (P = 0.96), marbling (P = 0.73), or quality grade (P = 0.10). However, the LM from steers fed diets formulated with Morex and SM5 barley varieties tended to be lighter (higher L* values, P = 0.08) than the LM from steers fed the corn-based diet. Additionally, fat from steers fed corn tended to be more yellow (higher Hunter b* values, P = 0.09) than fat from steers fed barley-based diets. Although grain source had only minimal effects on the fatty acid composition of subcutaneous fat samples, pentadecanoic acid (15:0) was greater (P < 0.05) in fat from steers fed SM3 and Steptoe barley varieties than in fat from steers fed corn. Stearic acid (18:0) concentrations were higher (P < 0.05) in fat samples from steers fed corn than in those fed the experimental barley lines (SM3 and SM5). Conversely, fat samples from steers fed Steptoe and SM5 barley had greater (P < 0.05) gadoleic acid (20:1) concentrations than fat from steers fed corn or Morex variety. Although the variety/line of barley included in the finishing diet may affect LM and fat color, grain-source (barley vs. corn) had little effect on beef carcass quality and yield grades and did not greatly alter the fatty acid composition of subcutaneous fat.
Key Words: Barley • Beef Cattle • Color • Corn • Fatty acids • Subcutaneous Fat
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Introduction
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Feedlots in the northern U.S. states, as well as Canada, typically feed barley-based diets to finishing cattle, whereas corn and milo are the preferred concentrates in feedlots located in the Southwest and Southern Plains states. Although environmental differences between these areas dictate the cultivation of available feedstuffs, there remain prejudices against inclusion of some grains and other by-product feeds in finishing diets based on unfounded concerns of these feedstuffs on cattle performances and carcass merit. Yet Boss and Bowman (1996)
reported similar growth rates between cattle fed barley or corn. More importantly, feeding cattle barley has been shown to improve beef carcass quality grades (Boss and Bowman, 1996), carcass weight, and LM area (Ovenell-Roy et al., 1998) compared with feeding corn. Maltin et al. (1998) reported an increase in heme pigments in beef from bulls finished on corn- or barley-based diets, suggesting that beef color may be redder when cattle are fed barley. Nelson et al. (2000), however, did not find any color differences between barley- and corn-fed beef. Additionally, Jeremiah et al. (1998) demonstrated that the source of dietary grain fed generally failed to produce any important effects on the cooking properties or palatability attributes of beef.
There are minor differences in the fatty acid composition between corn and barley (Weber, 1987; Morrison 1993); however, the differences between the two grains may result in changes in the fatty acid composition of beef (Nelson et al., 2000). Moreover, little is known about how genetic changes made in new barley lines/varieties might affect beef carcass quality and fatty acid composition of beef fat. Therefore, the purpose of this study was to evaluate the effect of diets based on corn and different barley varieties on the carcass composition, initial color of the meat, and the fatty acid composition of the subcutaneous fat.
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Materials and Methods
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Crossbred steers, with an initial BW of 391 kg, were assigned randomly to one of five finishing diets composed primarily of corn (n = 9), Morex barley (n = 9), Steptoe barley (n = 9), or two experimental barley lines SM3 (n = 9) and SM5 (n = 9). Barley varieties/lines used in this experiment were selected for their growth characteristics and digestibility, and were grown near Havre, MT. Morex is a six-rowed, malting barley adapted to growing in areas of Minnesota, North Dakota, and South Dakota and is the American Malting Barley Association’s standard malting variety (Rasmusson and Wilcoxson, 1979). Steptoe barley is a six-rowed, feed-type barley adapted to high- and low-rainfall areas of Washington, Idaho, Eastern Oregon, and Montana (Muir and Nilan, 1973). The experimental barley lines, SM3 and SM5, are backcrossed lines from Steptoe x Morex, and were developed to have the Morex allele at the ABA3 marker locus, which has been shown to mark digestibility (Gibson et al., 1994).
The experimental protocol for this experiment was approved before initiation by the Montana State University Animal Care Committee. Diets (DM basis) were formulated to be isonitrogenous (2.24% N) and isocaloric (2.01 Mcal/kg NEm and 1.35 Mcal/kg NEg), and all grain sources were cracked before feeding (83% grain, DM basis). Chopped barley straw (6%, DM basis) was included in all diets as roughage source. Steers were adjusted to their treatment diets during a 28-d adaptation period, and subsequently implanted with Implus-S (Upjohn, Kalamazoo, MI) at 28 d. Steers were fed daily at 0900 during the 112-d feeding trial, and had ad libitum access to water. There were two pens per treatment.
When 70% of all steers were visually estimated to grade USDA Choice, steers were transported 9 h (861 km) and slaughtered after a 12-h rest period at a commercial processing plant. After a 24-h chill at 4°C, carcass quality and yield grade data (USDA, 1997) were collected by a trained, experienced evaluator, and objective color (L*, a*, and b* values) of the LM and subcutaneous fat was measured with a Hunter Miniscan (Hunter Lab., Reston, VA) using illuminant A and a 10° angle of incidence after carcasses had been ribbed for USDA grading and passed the grading station in the plant (approximately 40 m after ribbing). Then, the subcutaneous fat opposite the LM (10th- to 12th-rib region) was excised from each carcass, and frozen at (80°C for fatty acid analysis.
Fatty Acid Composition
Two grams of fat tissue was homogenized using a Polytron Homogenizer (Fisher Scientific, Denver, CO) as described by Bligh and Dyer (1959). Extracted lipids were converted to methyl esters according to the procedures of Ramamurthi and McCurdy (1993) and analyzed in duplicate using a Varian 3400 GC equipped with a flame ionization detector and an autosampler (Varian Inc., Palo Alto, CA). The 30-m fused-silica capillary column (BPX-70; Rose Scientific, Edmonton, AB) had an i.d. of 0.22 mm and a film thickness of 0.25 µm. The column was held initially for 5 min at 140°C, raised to 170°C at a rate of 6°C/min, then to 190°C at a rate of 6°C/min, held for 2 min, and then temperature was raised to 220° at rate of 6°/min. Inlet temperature was 220°C and the detector temperature was 260°C. Split flow rate of carrier gas (nitrogen) was 60 mL/min. Data were collected, detected, and integrated, and response factors were estimated from standards (Nu-Chek-Prep Inc., Elysian, MN) run under identical conditions.
Statistical Analyses
Data were analyzed using the GLM procedure of SAS with individual steer as the experimental unit. Grain in diet was included as the lone main effect in the model. Least squares means were computed and statistically separated by the LSD method. Means were considered statistically different when the treatment F-test was P < 0.05.
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Results and Discussion
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Carcass Quality
Grain source in finishing diets had no effects on hot carcass weight (P = 0.15), fat thickness (P = 0.58), LM area (P = 0.57), percentage of internal fat (P = 0.52), or USDA yield grade (P = 0.96) (Table 1). Additionally, carcass maturity, marbling scores (P = 0.73), and resulting USDA quality grades (P = 0.10) did not differ, regardless of dietary treatment (Table 1). These results agree with those of Nelson et al. (2000) but conflict with results of Boss and Bowman (1996) and Ovenell-Roy et al. (1998). Nelson et al. (2000) reported no differences in carcass traits between steers that had been fed finishing diets based on barley or corn. Boss and Bowman (1996), however, reported higher USDA quality grades for carcass from steers that had been fed diets based on Harrington barley variety compared with carcasses of steers fed either corn or two other barley varieties (Gunhilde or Medallion). Furthermore, Ovenell-Roy et al. (1998) reported heavier carcass weights and larger LM area when steers were fed diets based on barley.
Lean from steers fed Morex and SM5 barley tended to be lighter (higher Hunter L* values; P = 0.08) than the LM from steers fed corn (Figure 1). Additionally, fat from steers fed corn tended to be more yellow (highest Hunter b* values; P = 0.09) than fat from steers fed barley (Figure 2). These results are not supported by those of Nelson et al. (2000), who found no affect of finishing diet (barley- vs. corn-based) on lean color. Yet McCurdy et al. (1981) reported that sensory panelists scored fat from roasts from steers fed longer on a high concentrate barley-based diet whiter than short-term fed animals. Maltin et al. (1998) reported an increase in heme pigments in meat from bulls finished on barley than that from bulls finished on silage-based diets. This observation suggests that beef from cattle fed a barley-based diet should be redder; however, results of the current study do not support this theory. The increase in lightness could be associated with antemortem muscle glycogen content and its relationship with ultimate pH or rate of pH decline postmortem. Immonen et al. (2000a,b) reported that high-energy diets increased glycogen stores and decreased ultimate pH compared with roughage-based, low-energy diets. There is, however, no indication that the type of grain a diet is based on will affect glycogen reserves or the rate of pH decline in meat.
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Figure 1. Comparison of corn and barley varieties on objective color measures of the LM. Y-Axis values are arbitrary units. The L* values are a measure of darkness to lightness (a higher value indicates a lighter color); a* values are a measure of redness (a higher value indicates a redder color); and b* values are a measure of yellowness (a higher value indicates a more yellow color). Bars for L* values without a common letter differ (P = 0.09).
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Figure 2. Comparison of corn and barley varieties on objective color measures of subcutaneous fat. Y-Axis values are arbitrary units. The L* values are a measure of darkness to lightness (a higher value indicates a lighter color); a* values are a measure of redness (a higher value indicates a redder color); and b* values are a measure of yellowness (a higher value indicates a more yellow color). Bars for b* values without a common letter differ (P = 0.08).
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Fatty Acid Composition
Grain in the diet fed to steers had only minor affects on the fatty acid composition of subcutaneous fat (Table 2). Pentadecanoic acid (15:0) content was higher (P < 0.05) in fat from steers fed SM3 and Steptoe than in fat from steers fed corn, whereas stearic acid (18:0) was highest in fat from steers fed corn, which was greater than (P < 0.05) in fat from steers fed SM3 and SM5. Gadoleic acid (20:1) was higher (P = 0.05) in fat of steers fed SM5 and Steptoe barley than in fat of steers fed diets based on either corn or Morex barley. Docosahexaenoic acid (22:6) was not found in significant quantities in the fat from cattle fed any of the diets but was found most (P < 0.05) in the fat of steers fed corn. These minor alterations in fatty acid composition had no (P > 0.05) appreciable effects on levels of total saturated, monounsaturated, or polyunsaturated fatty acids, as well as the saturated-to-unsaturated ratio in beef subcutaneous fat.
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Table 2. Fatty acid composition (% of total) of fat from steers fed finishing diets based on four barley varieties and corn
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Nelson et al. (2000) reported that corn had higher levels of 18:1 and 18:2 than barley, whereas barley had higher levels of 16:0 and 16:1 than corn. These increased levels were not translated into the LM. Additionally, Nelson et al. (2000) failed to detect changes in 14:0, 17:0, and 17:1 in meat from steers fed corn having more 14:0 and less 17:0 and 17:1. In the current study, fatty acid composition was affected by variety of barley in the diet, which could explain differences between previously published and present results. This information also could affect utilization of newly developed barley varieties. If alterations in the barley translate to increased unsaturated fatty acids in meat or to a more acceptable fatty acid profile, it could change the perception of barley as a grain for cattle finishing diets.
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Implications
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Results of the current study are interpreted to suggest that there are no substantial differences between feeding corn- or barley-based finishing diets on beef carcass quality or yield grades. Although barley varieties/lines used in the present experiment resulted in subtle improvements in beef and fat color, as well as subcutaneous fatty acid profiles, additional research is needed to determine how the numerous barley varieties/lines affect beef quality, including cooked beef palatability.
1 Correspondence: P.O. Box 172900 (phone: 406-994-7352; fax: 406-994-5589; e-mail: jboles{at}montana.edu).
Received for publication July 10, 2003.
Accepted for publication March 31, 2004.
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Abstract
Introduction
