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Author: B.S. CLYBURN, C.R. RICHARDSON, J.L. MONTGOMERY, G.V. POLLARD, A.D. HERRING and M.F. MILLER - Texas Tech University (Courtesy of Alltech Inc.)
Effects of vitamin E level and selenium (Se) supplement form on performance and carcass characteristics were evaluated in a completely randomized design involving 96 Angus crossbred steers (374 ± 34.3 kg). Two sources of dietary selenium, sodium selenite and organic selenium (Sel-Plex selenium yeast, Alltech Inc.) added at 0.3 mg Se/kg and three levels of vitamin E (500, 250, and 125 IU/hd/d) were evaluated over a 103 day finishing period.
Steers were divided into six equal groups and fed diets based on steamflaked corn with 10% roughage. The basal ration was a typical southwestern US feedlot diet with all test diets formulated to be isonitrogenous and isocaloric. Steers given organic selenium showed improvements (P<0.10) in performance measurements during the first 56 days of the finishing study.
Cattle receiving inorganic selenium and a moderate level of vitamin E had a larger (P<0.10) longissimus muscle area. Selenium source and vitamin E level did not affect WBS values. Retail display color characteristics, lean muscle lightness (L*), measure of lean redness (a*), and lean muscle yellowness (b*) were measured on strip loin steaks for four different aging treatments. No difference was detected for lean muscle lightness between steaks from the inorganic selenium treatment and 500 IU vitamin E and organic selenium plus 250 IU vitamin E at 7 days aging compared to the same treatments when steaks were aged for 14 days. No difference was detected between the inorganic selenium and 250 IU vitamin E and the organic Se with 125 IU vitamin E at 7 and 35 days, respectively. Steaks from steers not fed supplemental vitamin E or selenium at all four aging treatment times showed no lean muscle lightness difference (P>0.05) from the organic selenium treatments with 125 IU and 500 IU vitamin E nor the inorganic selenium treatments after 35 days of aging. No differences were detected among treatments for all other retail display color variables measured.
Introduction
During the 1930s and 1940s selenium was considered to be a powerful toxin in livestock. However, during the late 1950s selenium was found to be an essential nutrient for livestock in small amounts (Mahan, 1999; Wolffram, 1999). In 1987, the Food and Drug Administration (FDA) approved the addition of selenium (sodium selenite or sodium selenate) to livestock and poultry diets at a 0.3 mg/kg concentration (Ullrey, 1992). Since that time, several changes have been made with regard to the level at which selenium can be administered in feeds for various animals. In August 1997, a final rule was published by the FDA that supports 3.0 mg/hd/d for beef cattle.
There have been numerous reports about the clinical importance of selenium in the prevention of white muscle disease in sheep and goats (McDowell, 1992). Normally, inorganic sources of selenium, such as sodium Selenite and sodium selenate, have been used in feed supplements. However, organic selenium sources, such as selenium-enriched yeast, have also become available for animal feeds. Edens (1996) showed that the use of seleniumenriched yeast, in comparison to sodium selenite, resulted in a reduction in the amount of drip loss from poultry muscle. However, few data are available on animal performance and carcass quality responses to dietary selenium source in beef cattle.
Selenium and vitamin E are nutritionally associated because of their relatively common deficiency symptoms. There have been a number of studies indicating a relationship between selenium and vitamin E in animal health (Van Ryssen et al., 1989; Weiss et al., 1990).
Vitamin E has been recognized as an essential nutrient for growth and health of all species of animals (McDowell, 1989). The diverse roles of vitamin E are due to its involvement in nutritional myopathy, prostaglandin biosynthesis, and immune response (Liu et al., 1995; Tengerdy, 1989). Asghar et al. (1991) showed improvements in animal performance when pigs were supplemented with 100 mg vitamin E/kg of feed. Vitamin E functions as a fat soluble antioxidant in cell membranes, primarily in the form of α-tocopherol (Brody, 1999; Sherbeck et al., 1995; Arnold et al., 1993). Supplementation of dietary vitamin E above animal requirements has been successful in reducing lipid oxidation in meat samples (Buckley et al., 1995).
Meat color is an important sensory characteristic by which consumers distinguish quality of meat (Faustman, 1994). Myoglobin is the primary pigment associated with color in meat. Myoglobin can be oxidized to metmyoglobin during retail display resulting in an undesirable brown color (Faustman, 1994; Zerby et al., 1999). Vitamin E is a potent antioxidant and has been shown to reduce the rate of lipid oxidation (Cannon et al., 1996), decrease drip loss, and improve overall meat quality (Asghar et al., 1991; Monahan et al., 1990a; 1990b). Color lightness is an extremely critical component associated with the appearance of fresh red meat and has substantial influence on purchase decisions (Sherbeck et al., 1995; Liu et al., 1996). Consumers have learned through experience that the desirable color of fresh beef is a bright cherry red color and any deviation from this has been associated with a degree of unacceptability (Kropf, 1980). Consumer-perceived freshness primarily determines retail display life, or the length of time the product displays the bright, cherry red color. Extending that period of time should greatly improve retail sale revenues (Sherbeck et al., 1995).
The objectives of this research were to determine the effects of organic or inorganic selenium along with vitamin E on performance, carcass characteristics, meat quality, and sensory characteristics of growing/finishing feedlot steers.
Materials and methods
Ninety-six Angus crossbred steers (374 ± 34.3 kg) were utilized in an experiment to compare the effects organic and inorganic selenium supplementation with different levels of vitamin E on performance, carcass characteristics, meat quality, and sensory characteristics. The feeding study was conducted at the Alltech Biotechnology Research Feedlot located on the Texas Tech University research farm on the southern high plains during the fall and winter of 1999.
Steers were divided by weight into 24 pens (four steers per pen and four pens per treatment) and fed for 103 days. Feed for each treatment was individually batched and delivered at approximately 0900 hrs each morning. Prior to feeding, feed remaining in the bunks was visually estimated and used to adjust feed amounts offered.
Typical feedlot diets used in this study were based on steam-flaked corn and 10% roughage from cottonseed hulls and chopped alfalfa hay (Table 1). All diets were formulated to meet or exceed requirements for crude protein, calcium, phosphorus, and vitamin A (NRC, 1996). Selenium was added to the diet to supply 0 or 3 mg Se per head daily in the form of inorganic selenium (sodium selenite) or organic selenium from yeast (Sel- Plex, Alltech Inc.). Vitamin E was added at either 125, 250, or 500 IU per head to provide the following dietary treatments:
1) Basal diet (no added vitamin E or Se)
2) 3.0 mg Se/head/day from Sel-Plex and 250 IU vitamin E
3 3.0 mg Se/head/day from selenite and 250 IU vitamin E
4) 3.0 mg Se/head/day from Sel-Plex and 125 IU vitamin E
5) 3.0 mg Se/head/day from selenite and 500 IU vitamin E
6) 3.0 mg Se/head/day from Sel-Plex and 500 IU vitamin E
Table 1. Composition (%) of experimental diets.
aFormulated to meet NRC (1996) requirements for beef cattle containing cottonseed meal, calcium carbonate, dicalcium phosphate, potassium chloride, magnesium oxide, ammonium sulfate, salt, cobalt carbonate, copper sulfate, iron sulfate, EDDI, manganese oxide, zinc sulfate, vitamin A, monensin, and tylosin. No added selenium or vitamin E.
bSodium selenite premix 1 = 3 mg/hd/d.
cSel-Plex premix 1 = 3 mg/hd/d.
dVitamin E premix 0.25 = 125 IU/hd/d, 0.50 = 250 IU/hd/d, and 1.0 = 500 IU/hd/d of vitamin E.
Individual animal weights were recorded at 28 day intervals during the experiment. Average daily gain (ADG), dry matter intake (DMI) and feed efficiency (F:G) ratios were calculated for each 28 day period. At the conclusion of the study, steers were transported to a commercial packing plant where final yield grade, dressing percent, longissimus muscle area, quality grade, kidney, pelvic and heart (KPH) fat, and fat thickness were recorded by trained personnel and loin steaks were obtained from two steers from each pen for retail and display measurements.
Steaks, 1.3 cm thick, were placed in a coffin-style retail display case (Tyler Refrigeration Corporation, Model DGC6, Niles, MI) at the Texas Tech University Meat Laboratory. Objective color measurements (L*, a*, and b*), on a 0 to 100 range, were taken daily for each aging treatment with a Hunter Miniscan XE Plus (Hunter Laboratories, Model MSXP-4500L, Reston, VA). Warner Bratzler shear force was determined by cooking each steak to 71°C on a belt grill (MagiKich’n, Model MagiGrill TBG 60, Quakertown, PA). Steaks were weighed before and after cooking to determine cooking loss. Six, 1.3 cm diameter cores were taken from each steak parallel to the muscle fiber orientation. Each was sheared once and the six values were averaged to determine shear value of each steak.
One steak from each strip loin for each aging treatment was cooked to 71°C and used for sensory evaluations. Eight trained panelists scored the steaks for initial and sustained juiciness (1= extremely dry, 8 = extremely juicy), initial and sustained tenderness (1= extremely tough, 8 = extremely tender), beef flavor intensity (1= extremely bland, 8 = extremely intense), beef flavor characteristic (1= extremely uncharacteristic beef flavor, 8 = extremely characteristic beef flavor), and overall mouthfeel (1 = extreme non-beef-like mouthfeel, 8 = extreme beef-like mouthfeel).
Performance carcass characteristics, meat quality and sensory characteristics were analyzed with pen as the experimental unit. A completely randomized design was used, and computations were made with the GLM procedure of SAS (1995). The following five orthogonal contrasts were used to evaluate treatment effects:
1) Control vs. the average of all other treatments
2) Average of the Sel-Plex vs. the average of the selenite selenium treatments
3) Sel-Plex Se/125 IU vitamin E vs. selenite Se/500 IU vitamin E
4) Sel-Plex Se/250 IU vitamin E vs. selenite Se/500 IU vitamin E
5) Sel-Plex Se/125 IU vitamin E vs. selenite Se/250 IU vitamin E
Results and discussion
PERFORMANCE EFFECTS
Selenium source and supplemental vitamin E level did not affect overall performance of steers (Table 2). These results are consistent with those of Mahan and Parrett (1996), Ortman and Pehrson (1998) and Mahan (1999), who demonstrated no overall growth or performance response to selenium form and various levels of vitamin E added to finishing swine diets. These results are also in agreement with Nicholson et al. (1991) who found no effect on ADG or F:G of calves supplemented with different selenium sources.
While there were no significant differences for performance over the entire feeding period, orthogonal contrasts revealed differences during the growing period (Table 2, Figure 1). During the first 28 days, cattle fed diets containing Sel-Plex selenium had higher (P = 0.09) ADG compared to those fed inorganic selenium. Improvements in daily gain were also detected for cattle given Sel-Plex plus either 125 (P = 0.05) or 250 IU (P = 0.02) vitamin E when compared to the group given inorganic selenium plus 500 IU vitamin E. Furthermore, at 56 days cattle given Sel-Plex plus 125 or 250 IU vitamin E continued to have higher daily gains compared to those given selenite plus 500 IU vitamin E (P = 0.09 and 0.08, respectively).
Dry matter intake was similar among treatments, except at day 56. Steers fed the non-supplemented control diet had higher DMI (P = 0.0001) at 56 days when compared to the average of all other treatments. Furthermore, DMI for cattle fed Sel-Plex with 125 IU vitamin E decreased (P= 0.02) by 7% compared to the group receiving selenite plus 500 IU of vitamin E. At 56 days steers fed the nonsupplemented basal diet had a reduced F:G (P = 0.02) when contrasted with the average of all other treatments. During the same period, improved efficiencies were noted for cattle given Sel-Plex with either 125 or 250 IU vitamin E (P=0.01 and 0.02, respectively), when compared to those fed diets containing selenite and 500 IU vitamin E. Responses in efficiency were similar at 84 days with cattle fed Sel-Plex and either 125 or 250 IU vitamin E being more efficient (P=0.03 and P=0.04) than cattle receiving selenite and 500 IU vitamin E. While steers fed Sel-Plex with 125 or 250 IU vitamin E were more efficient for most of the feeding study, in the last 21 days of the study there was a decline in ADG that affected overall efficiency.
Cattle in all treatments experienced a decrease in blood cortisol level; however, this decrease could not be attributed to selenium source or vitamin E level (Table 3).
Table 2. Effects of vitamin E level and selenium source on performance of finishing beef steers.
aBasal diet: no added vitamin E or Se.
bPooled standard error of treatment means, n = 4 pens/treatment.
cOrthogonal contrast: 1) control vs the average of all other treatments; 2) Organic vs Inorganic Se; 3) Sel-Plex 125 vs selenite 500; 4) Sel-Plex 250 vs selenite 500; and 5) Sel-Plex 125 vs. selenite 250.
dOSL = observed significance level of orthogonal contrast; NS = non-significant, P>0.10.
Figure 1. Effect of selenium source and vitamin E level on average daily gain (ADG) of steers days 0-28 and 0-56.
Table 3. Effects of vitamin E level and selenium source on blood cortisol levels.
aControl = no added vitamin E or Se in diet.
bPooled standard error of treatment means, n = four pens/treatment.
cOSL: observed significance level of orthogonal contrast; NS: non-significant
CARCASS CHARACTERISTICS
The same orthogonal contrast used to compare means for growth performance was used to compare effects of treatments on carcass characteristics. Neither selenium source nor vitamin E level influenced hot carcass weight, final yield grade, fat thickness, or marbling score (Table 4).
While few differences were noted for carcass data among treatments, cattle fed the non-supplemented basal diet had higher (P<0.01) dressing percentage when compared to the average of all other treatments. The Sel-Plex and 125 IU vitamin E group had more KPH fat (P<0.10) than cattle given selenite and 500 IU vitamin E. The average of the Sel-Plex treatments had lower LMA (P<0.10) compared to selenite treatments. No statistical analyses were performed on quality grade percentage; however, more cattle fed Sel-Plex and 250 IU vitamin E graded Choice. On average, 83% of the cattle graded USDA Choice or better, with an average fat thickness of 1.49 cm, indicating that the cattle had reached the desired degree of finish by the end of the 103 day study.
Table 4. Effects of vitamin E level and selenium source on carcass characteristics of finishing feedlot cattle.
aControl: no added vitamin E or Se.
bPooled standard error of treatment means, n = four pens/treatment.
cOrthogonal contrast: 1) control vs the average of all other treatments; 2) Sel-Plex vs selenite; 3) Sel-Plex 125 vs selenite 500; 4) Sel-Plex 250 vs selenite 500; and 5) Sel-Plex 125 vs. selenite. dOSL: observed significance level of orthogonal contrast; NS = non-significant, P>0.10.
e300 = Slight; 400 = Small; 500 = Modest; 600 = Moderate; 700 = Slightly abundant.
fChoice % includes cattle that graded Prime.
MEAT QUALITY
Orthogonal contrasts were employed to compare effects of treatment on meat quality and sensory characteristics. Meat from cattle fed the nonsupplemented basal diet tended to have a lower moisture percentage when compared to all other treatments (Table 5). The Sel-Plex treatment with the lowest level of vitamin E showed a decrease in crude protein when compared to selenite and 250 IU vitamin E and 500 IU vitamin E (P =0.05 and P = 0.03 respectively). The average of the Sel-Plex treatments tended to show an increase for fat deposition. The Sel-Plex plus 250 IU vitamin E expressed a greater percentage of fat deposition (P = 0.01) when contrasted with selenite and 500 IU vitamin E; and Sel-Plex plus 125 IU vitamin E tended to have a larger percentage of fat deposition compared to selenite and 500 IU vitamin E. Neither selenium source nor dietary level of vitamin E affected the concentration of vitamin E in strip loin steaks, liver selenium concentration or WBS values (Table 6 and 7). No differences were noted among treatments for lipid oxidation for meat aged for 7 (Figure 2) and 35 days (Figure 3).
Table 5. Effects of vitamin E level and selenium source on moisture (%), crude protein (%) and crude fat content (%) of meat.
aControl: no added vitamin E or Se.
bPooled standard error of treatment means, n = four pens/treatment.
cOrthogonal contrast: 1) control vs the average of all other treatments; 2) Sel-Plex vs selenite; 3) Sel-Plex 125 vs selenite 500; 4) Sel-Plex 250 vs selenite 500; and 5) Sel-Plex 125 vs. selenite.
dOSL: observed significance level of orthogonal contrast; NS = non-significant, P>0.10.
Table 6. Effects of level of vitamin E and selenium source on vitamin E and selenium concentration in tissue.
aControl: no added vitamin E or Se.
bPooled standard error of treatment means, n = four pens/treatment.
cSingle-test tube method for the flourometric microdetermination of Se (Spallholz et al., 1978) measured in fluorescent units/g of liver.
dOSL: observed significance level of orthogonal contrast; NS = non-significant
Table 7. Effects of vitamin E level and selenium source on Warner Bratzler shear force values for 7 and 35 days aging.
aControl: no added vitamin E or Se.
bPooled standard error of treatment means, n = four pens/treatment.
cOSL: observed significance level of orthogonal contrast; NS = non-significant
Figure 2. Lipid oxidation for retail display steaks aged 7 days.
Figure 3. Lipid oxidation for retail display steaks aged for 35 days.
Neither selenium form nor dietary level of vitamin E influenced drip or purge loss from the meat (Table 8). There tended to be an increase in cooking loss in meat aged 7 days for treated animals; and animals receiving selenite tended to have an increase in cooking loss compared to animals supplemented with organic selenium (Table 9). Cattle supplemented with inorganic selenium tended (P>0.10) to show an increase in cooking loss in meat aged 14 days over the animals receiving the organic form. During the same aging treatment organic selenium plus 125 IU vitamin E had less cooking loss (P = 0.09) when contrasted with inorganic selenium and 500 IU of vitamin E. The average of the Sel-Plex treatments showed an increase in cooking loss (P = 0.04) over the inorganic selenium treatments when the meat was aged for 21 days. Sel-Plex with 250 IU vitamin E had a greater cooking percentage (P = 0.004) when compared to the inorganic selenium treatment with 500 IU vitamin E after 21 days aging. An increase in cooking loss was detected for the Sel-Plex treatments when the meat was aged for 35 days. Additionally there tended to be an increase in cooking loss for Sel- Plex plus 125 IU vitamin E when compared to both inorganic selenium treatments. Increases in cooking loss may be the result of more bound water attached to the myofibrils.
Table 8. Effects of vitamin E level and selenium source on drip and purge loss.
aControl: no added vitamin E or Se.
bPooled standard error of treatment means, n = four pens/treatment.
cOSL: observed significance level of orthogonal contrast; NS: non-significant.
Table 9. Effects of vitamin E level and selenium source on cooking loss for meat aged 7, 14, 21, and 35 days.
aControl: no added vitamin E or Se.
bPooled standard error of treatment means, n = four pens/treatment.
cOrthogonal contrast: 1) control vs the average of all other treatments; 2) Sel-Plex vs selenite; 3) Sel-Plex 125 vs selenite 500; 4) Sel-Plex 250 vs selenite 500; and 5) Sel-Plex 125 vs. selenite.
dOSL: observed significance level of orthogonal contrast; NS: non-significant.
Steaks were placed in a retail case for 7, 14, 21, and 35 days and measured with a Hunter spectrophotometer to obtain L* a* and b* color measurements (Table 10). Retail display color characteristics were analyzed utilizing the PROC GLM procedure in SAS. No statistical differences were detected for lean muscle lightness (L*) between steaks from the selenite plus 500 IU vitamin E and the Sel-Plex plus 250 IU vitamin E at 7 days aging compared to the same treatments when steaks were aged for 14 days. Additionally, no difference in lean color lightness was detected between the 7 and 14 day aging treatments for the steaks from steers fed Sel-Plex with 500 IU vitamin E. No differences were noted between the organic selenium treatments with 250 IU vitamin E when steaks were aged for 14 and 35 days, respectively. Furthermore, inorganic along with 250 IU vitamin E at 7 days aging showed no difference in lean muscle lightness when compared with the Sel-Plex treatment with 125 IU vitamin E at 35 days aging. Steaks from steers fed no supplemental dietary vitamin E or selenium at all four aging treatments (7, 14, 21, and 35 days) showed no lean muscle lightness difference from the organic selenium plus 125 IU or 500 IU vitamin E treatments nor the inorganic selenium treatments at 35 days of aging. No differences were detected among treatments for the other retail display color variables measured.
Table 10. Age*treatment effects of vitamin E level and selenium source on retail display of meat aged 7, 14, 21, and 35 days.
aControl: no added vitamin E or Se.
bPooled standard error of treatment means, n = four pens/treatment. ABCDEFGHIJ Indicates differences at (P<0.05).
Table 11. Effects of vitamin E level and selenium source on sensory panel scores for meat aged 7, 14, 21, and 35 days.
aControl: no added vitamin E or Se.
bPooled standard error of treatment means, n = four pens/treatment.
cOrthogonal contrast: 1) control vs the average of all other treatments; 2) Sel-Plex vs selenite; 3) Sel-Plex 125 vs selenite 500; 4) Sel-Plex 250 vs selenite 500; and 5) Sel-Plex 125 vs. selenite.
dOSL: observed significance level of orthogonal contrast; NS = non-significant, P>0.10.
Sensory panel results are reported in Table 11 for juiciness (initial and sustained), tenderness (initial and sustained), flavor intensity, beef flavor, and mouth feel. Initial juiciness, sustained juiciness and mouth feel were relatively unaffected by selenium source or vitamin E level over the 7, 14, 21, and 35 day aging treatments. There was a trend (P>0.10) for taste preference, as indicated by beef flavor and flavor intensity, to be improved by organic selenium and lower levels of vitamin E across the different aging treatments. However, during the sensory panel evaluations no other consistent results were recorded.
Conclusions
Performance over the entire 103 day feeding trial was unaffected; however, cattle supplemented with Sel-Plex showed improvements in performance during the first 56 days on feed. Supplementation of feedlot steers with inorganic selenium increased LMA; and in addition selenium and vitamin E both decreased dressing percentage. Organic selenium and low levels of vitamin E increased the percentage of KPH. Lipid oxidation of retail steaks was unaffected when steaks were aged for 7 and 35 days.
Lightness of lean muscle of steaks aged 7, 14, and 35 days was improved with 50% less vitamin E when organic selenium was added to the diet. Taste appeal of steaks, as indicated by beef flavor and flavor intensity, was improved by the addition of organic selenium, as well. Using simulated retail display conditions, vitamin E and organic selenium treated retail items remained acceptable for a longer period of time than did control retail steaks. These advantages should improve the profitability of beef in the retail case. Dietary supplementation of vitamin E and selenium potentially stabilizes polyunsaturated fatty acids and cholesterol in muscle thus protecting against oxidative deterioration.
This effect is primarily due to the inclusion of micronutrients and vitamins into subcellular membranes, where it has the potential to optimize the antioxidant capacity of the system and may improve physical stability. Increased attention to vitamin and mineral requirements of domestic animals may improve food quality and acceptability of muscle foods by the consumer through improved shelf-life and color perception.
Organic selenium may be effective in improving beef retail sales through improved customer preference and improved eating quality of steaks compared to diets supplemented with inorganic selenium sources. While organic selenium enhanced performance during the receiving and growing periods only, it may be beneficial to include organic selenium throughout the entire feeding period due to increased consumer acceptability of meat products.
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Authors: B.S. CLYBURN, C.R. RICHARDSON, J.L. MONTGOMERY, G.V. POLLARD, A.D. HERRING and M.F. MILLER
Texas Tech University, Lubbock, Texas, USA
Author: B.S. CLYBURN, C.R. RICHARDSON, J.L. MONTGOMERY, G.V. POLLARD, A.D. HERRING and M.F. MILLER - Texas Tech University (Courtesy of Alltech Inc.)
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