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Forage-Finished Beef Supplemented with Corn and Corn Oil
The Professional Animal Scientist 25 (2009):586–595
©2009 American Registry of Professional Animal Scientists
Forage-Finished Beef Supplemented with Corn and Corn Oil
V. A. Corriher,*1 G. M. Hill,* T. D. Pringle,† and B. G. Mullinix Jr.‡ *Department of Animal and Dairy Science, University of Georgia, Tifton 31793; †Department of Animal and Dairy Science, University of Georgia, Athens 30602; and ‡Experimental Statistics, Texas A&M University, Lubbock 79403
ABSTRACT Beef steers were finished on ryegrass with corn or corn + corn oil supplementation in a 2-yr experiment to determine effects on performance and conjugated linoleic acid tissue concentration, especially cis-9, trans-11 (c9,t11). Rib steak (longissimus dorsi, LM) and subcutaneous fat (SQ) samples were analyzed for long-chain fatty acid concentrations. Angus and Angus crossbred steers (yr 1, n = 18, initial BW 369.4 ± 29.1 kg; yr 2, n = 48; initial BW 364.1 ± 1.07 kg) were backgrounded on rye pasture for 71 d (ADG 1.78 ± 0.11 kg) and 41 d (ADG 1.24 ± 0.77 kg), respectively, in yr 1 and yr 2. After rye grazing, steers were assigned to ryegrass pastures (cv. Big Daddy; yr 1: 4 pastures, 1.62 ha each; yr 2: 6 pastures, 1.46 ha each) for 83 d in yr 1 and 112 d in yr 2, and fed corn at 1% BW, without or with corn + corn oil (0.075% BW). In yr 1, steer initial BW (n = 16; 424.3 ± 27.83 kg), 83-d ADG (1.78 vs. 1.89 kg), carcass weight (347.9 vs. 354.44 kg), and QG (12.27 vs. 12.61; 12 = US Select +) were similar for corn vs. corn + corn oil treatments. In yr 2, a ryegrass-only treatment was added to the corn and corn + corn oil treatments used in yr 1. Steers (n = 37, 1 Corresponding author: vacorriher@ ag.tamu.edu
initial BW 390.1 kg ± 27.4) assigned to ryegrass only (n = 9), corn (n = 14), or corn + corn oil (n = 14) treatments had respective 112-d ADG of 1.07, 1.65, and 1.62 kg (P < 0.01); carcass weights of 288.1, 321.4, and 326.0 kg (P < 0.01), and QG of 9.78, 10.57, and 10.29 (10 = US Select, P > 0.28). Feeding corn + corn oil decreased supplement intake in yr 1 (P < 0.03), but it did not improve ADG above feeding corn at 1% BW in either year. In yr 1, concentrations of c9,t11 were similar for corn and corn + corn oil in LM, but corn + corn oil had higher (P < 0.04) concentrations in SQ samples. In yr 2, concentration of c9,t11 was highest for LM (P < 0.03) and SQ (P < 0.02) in corn + corn oil compared with similar values for the ryegrass-only and corn treatments. Results indicate that addition of corn oil with corn may increase conjugated linoleic acid in beef steers finished on ryegrass pasture, but may not affect performance or QG. Key words: beef, forage, corn oil supplementation, carcass, fatty acid
INTRODUCTION Conjugated linoleic acid (CLA) is a collective term used to describe one or more positional and geometric isomers of linoleic acid (cis-9, cis-12octadecadienoic acid). Enhancing the
content of the cis-9, trans-11 isomer of CLA has acquired attention in the beef industry because of its anticarcinogenic and antiatherogenic effects (Scollan et al., 2006). Milk and beef represent the major sources of CLA in the human diet (Ritzenthaler et al., 2001). Although CLA are produced in the rumen by incomplete biohydrogenation of dietary C18:2n-6, CLA is also synthesized in adipose tissue and in the mammary gland by desaturation of C18:1 trans-11 (Griinari et al., 2000). Fat supplementation has become a common practice to increase dietary energy density for high-producing dairy cows and finishing steers. Forages and concentrates are the primary sources of lipid in the ruminant diet. Forages typically contain 2 to 3% of the DM of the leaf as lipid. Forages generally contain a higher concentration of linolenic acid (C18:3), whereas linoleic acid (C18:2) is the predominant fatty acid in cereal grains and seeds. Inclusion of plant oils or whole seeds in ruminant rations has been shown in several studies (Scollan et al., 2001; Mir et al., 2002; Noci et al., 2005b) to increase the concentrations of CLA and PUFA in meat. The CLA and n-3 PUFA concentrations in tissue are relatively high in pasture-fed beef cattle (French et al.,
Forage-finished beef supplemented with corn and corn oil
2000; Engle and Spears, 2004; Noci et al., 2005a). Pavan et al. (2007) reported increased vaccenic acid and CLA concentrations when steers grazing endophyte-free tall fescue were supplemented with corn oil at 0.75 g/kg BW. In that study, the cis-9, trans-11 isomer of CLA was increased when corn oil was supplemented to grazing steers. Feeding higher levels of forage in finishing diets appears to alter the ruminal biohydrogenation of linoleic acid, resulting in greater outflow of intermediates via the trans-11 pathway. Therefore, our objective was to determine the effect of corn oil supplementation on performance and carcass quality in steers finished on ryegrass pasture.
MATERIALS AND METHODS The 2-yr grazing experiment was conducted at The University of Georgia Tifton Beef Unit (Tifton, GA) between February and May 2007 and 2008. Steers for both years were implanted with Component (trenbolone acetate, estradiol, and tylosin tartrate; Ivy Animal Health, Overland Park, KS) on d 1 of each experiment. All cattle were managed under procedures approved by the University
of Georgia Institutional Animal Care and Use Committee.
Backgrounding of Steers During preliminary beef steer growing periods (yr 1 = 71 d; n = 18; yr 2 = 48 d; n = 48), steer yr 1 initial BW was 369.4 ± 29.1 kg, yr 2 initial BW was 364.09 ± 1.07 kg, and their age was 18 mo for yr 1 and 15 mo for yr 2. Steers were either Angus or Angus-crossbred steers; stocked at 2.0 steers/ha, they grazed rye pasture and had ADG of 1.78 ± 0.11 kg for yr 1 and ADG of 1.24 ± 0.77 kg for yr 2. Pastures (yr 1: 4 total pastures, 1.62 ha each; yr 2: 6 total pastures, 1.46 ha each) were harrowed September 21, 2006, and August 30, 2007, and drilled with Wrens Abruzzi Rye (Southern States Cooperative Inc., Richmond, VA) on October 28, 2006, and September 26, 2007, at 1.31 to 1.74 hectaliters/ha.
Grazing Experiment After rye grazing, beef steers (yr 1: n = 16, initial BW 424.3 ± 27.8 kg, age 18 mo; yr 2: n = 37, initial BW 390.1 ± 27.4 kg, age 15 mo; Angus and Angus-crossbred; stocking rate 2.24 head/ha) were fed ground corn
Table 1. Mean DM chemical and fatty acid composition of the different dietary components for steers grazing ryegrass pastures Item Component, % (DM basis) DM CP NDF ADF Total fatty acids, % Fatty acid, % of total C14:0 C16:0 C18:0 C18:1 C18:2 C18:3 Others1 Unidentified 1
Forage
Corn
Corn oil
Corn + corn oil
20 19.1 48.3 29.6 1.19
89.1 11.8 8.0 2.9 3.78
— — — — 91.9
73.5 8.9 7.6 3.0 5.17
0.4 14.6 1.2 1.7 10.6 68.4 1.7 1.4
0.07 13.36 2.31 23.10 54.06 1.30 0.67 0.0
<0.1 10.8 1.96 28.5 55.7 1.3 0.75 0.95
0 10.59 1.96 27.27 57.47 0.97 1.34 0.22
Sum of C12:0, C15:0, C16:1, C17:0, C20:0, C21:0, and C22:0.
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supplement (1% BW; Rumensin 200 mg/d, Eli Lilly & Co., Indianapolis, IN, supplied by W. B. Fleming Co., Tifton, GA; Table 1) without and with corn oil (0.075% BW) while grazing ryegrass pastures. Grazing was initiated after the establishment of ryegrass, and grazing was terminated at the end of the finishing period (typically 90 to 180 d). During yr 2, three treatments were used; negative control treatment steers grazed ryegrass only, and supplement treatment steers grazed ryegrass and were fed ground corn at 1% BW, without or with corn oil (0.075% BW). In yr 2, seven steers per pasture were initially assigned; however, ryegrass pastures could not sustain this stocking rate for the duration of the 112-d feeding interval. Initial BW was equalized for all 6 groups in initial assignments to 6 groups, which were randomly assigned to 3 treatments with 2 replicate pastures for each group. Ryegrass pastures (cv. Big Daddy; yr 1: 4 paddocks, 1.62 ha each; yr 2: 6 paddocks, 1.46 ha each) were fertilized with a blended fertilizer (24-6-12, N-P2O5-K2O, at 280 kg/ ha, on November 27, 2006, January 11, 2007, March 7, 2007, October 23, 2007, and February 21, 2008). Steers were ranked by BW and randomly assigned to dietary treatments for 83 d in yr 1 and for 112 d in yr 2. Supplements were fed free choice daily at 0800 h. Supplement refusals were weighed daily to determine intake. Initially, 42 steers were assigned to the 3 treatments in yr 2. However, only a total of 37 steers completed the experimental period. After 6 wk of the experimental period, the stocking rate was reduced for grazingonly treatments because of a decline in forage mass. At 14-d intervals beginning in February, forage mass was estimated using a double sampling procedure. Four quadrats (0.1 m2) were clipped to ground level in each paddock and clipped samples were oven-dried. Pooled estimates of DM production were converted to a moisture-free basis using pooled DM values. Steers were weighed at 28-d intervals, and initial and final BW
588 were means of consecutive daily full weights. A commercial mineral [NaCl (maximum) 22.0%; Ca (maximum) 16.0%; P (minimum) 6.5%; Mg (minimum) 1.00%; Cu (minimum) 0.025%; Zn (minimum) 0.25%; Se (minimum) 0.0013%; Beef Cattle High Gain-B, W. B. Fleming Co.] was provided free choice along with water in all paddocks in yr 1. In yr 1, Rumensin was mixed with the corn that was fed to the steers. In yr 2, one treatment was ryegrass only; therefore, a mineral supplying an ionophore (Bovatec) was fed in the mineral supplement (Beef Cattle High Gain-B, W. B. Fleming Co.) along with water in each paddock.
Chemical and Fatty Acid Composition Analysis Forage and corn grain samples were lyophilized, ground through a Wiley mill (Arthur H. Thomas, Philadelphia, PA) equipped with a 1-mm screen, and stored at −20°C for subsequent analysis of OM, NDF, ADF, CP, total fatty acid percentage, and fatty acid profile. Organic matter was measured as the weight loss after combustion for 8 h at 500°C. The NDF and ADF were sequentially determined using an Ankom 200 fiber extractor (Ankom Technologies, Fairport, NY) according to the method of Van Soest et al. (1991). Crude protein concentration was determined by the combustion method with a Leco FP-2000 N analyzer (Leco Corp., St. Joseph, MI). Total fatty acid percentage and fatty acid profile were also determined for corn oil samples. Steers for both years were transported (1,609 km) to Cargill Taylor Beef (Wyalusing, PA) for slaughter. Rib sections were collected from each steer and shipped to The University of Georgia Meat Science and Technology Center in Athens. Samples of subcutaneous (SQ) adipose tissue and a 2.5-cm LM steak, which corresponded to a ribeye steak, were removed from the sections at the 13th rib. A second 2.5-cm LM steak from each carcass was frozen for subsequent sensory evaluations. Both SQ and LM sam-
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ples from each carcass were stored at −20°C, and before analysis, samples were pulverized in liquid nitrogen. Total lipids were extracted in duplicate from LM and SQ samples according to the procedures of Folch et al. (1957). Lipid extracts from SQ and LM samples were stored at −80°C for subsequent fatty acid determination. For wet tissue lipids, 1 g of ground muscle tissue or 0.4 g of ground SQ fat was extracted. The SQ and LM lipid extracts, containing approximately 2 mg of total lipids, based on the calculated percentage of lipids on a wet tissue basis, were transmethylated (Park and Goins, 1994). Fatty acid methyl esters were analyzed using an HP6850 gas chromatograph (Hewlett-Packard, San Fernando, CA) equipped with an HP7673A automatic sampler (Hewlett-Packard). Separations were accomplished using a 100-m Sp2560 capillary column (0.25 mm i.d. and 0.20-μm film thickness; Supelco, Bellefonte, PA) according to the method of Duckett et al. (2002). Column oven temperature increased from 150 to 160°C at 1°C per min, from 160 to 167°C at 0.2°C per min, from 167 to 225°C at 1.5°C per min, and was then held at 225°C for 16 min. The injector and detector temperatures were maintained at 250°C. Sample injection volume was 1 μL. Hydrogen was the carrier gas at a flow rate of 1 mL/min. Individual fatty acids were identified by comparison of retention times with standards (Sigma, St. Louis, MO; Supelco; Matreya, Pleasant Gap, PA). The fatty acids were quantified by incorporating an internal standard, methyl heptacosanoic acid (C27:0), into each sample during methylation and were expressed as grams per 100 g of tissue. The fatty acid compositions of forage, corn oil, and corn grain were determined by direct transmethylation of lyophilized samples according to the method of Park and Goins (1994) and were analyzed as SQ and intramuscular fatty acid methyl esters.
Palatability Measurements In yr 2, steaks were stored frozen until thawed and prepared for sensory evaluations. For the trained sensory evaluations, the steaks were thawed overnight at 4°C and broiled (model 450N Open-Hearth Broiler, Farberware, Bronx, NY) to an internal end point of 70°C (American Meat Science Association, 1995). Internal temperature was monitored by copper-constantan thermocouples (Omega Engineering, Stamford, CT) placed in the approximate geometric center of each steak. The steaks were served warm to an 8-member trained panel. The panel evaluated juiciness (1 = extremely dry to 8 = extremely juicy), flavor intensity (1 = extremely bland to 8 = extremely intense), overall tenderness (1 = extremely tough to 8 = extremely tender), amount of detectable connective tissue amount (1 = extremely abundant amount to 8 = none detected), and off-flavor (1 = extreme off-flavor to 6 = none detected).
Statistical Analyses Intake, BW gain, carcass variables, and long-chain fatty acid (LCFA) analyses were statistically analyzed as a completely randomized design using the MIXED procedure (SAS Institute, 2003) with pen of cattle as the experimental unit as a random effect and dietary treatment as a fixed effect. Treatment means were compared using the Satterthwaite test (SAS Institute, 2003). Year means were compared for corn and corn + corn oil treatments using the Satterthwaite test (SAS Institute, 2003). Least squares means are presented for main effects when interactions were not significant (P > 0.10); in addition, treatment means for the individual factors are presented in tables.
RESULTS AND DISCUSSION Grazing Experiment Pasture Quality. Forage available DM for both years of the study
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Table 2. Available ryegrass DM (kg/ha) in pastures being grazed by finishing steers, yr 1 Item1 February 9 March 7 March 23 April 6 April 20 1
Treatment 2, pasture 1
Treatment 2, pasture 4
Treatment 3, pasture 2
Treatment 3, pasture 3
Avg of 4 pastures
937 1,169 924 1,205 1,617
867 1,199 1,226 1,435 1,864
818 1,178 1,002 1,377 1,284
890 1,534 1,158 1,511 1,300
878 1,270 1,078 1,382 1,516
Each value is the mean of 4 ground-level forage samples. Treatment 2 = corn only; treatment 3 = corn + corn oil.
averaged 1,251.2 ± 258 kg/ha during the finishing period from January to May. Ryegrass DM availability was not different among treatments, years, or sampling dates (P > 0.10; Tables 2 and 3). Average DM production tended to increase during the experimental period as the grazing season advanced from winter to spring. Therefore, forage availability was not a limiting factor. Early rainfall and drought following the finishing interval during yr 1 contributed to the trend for increasing DM production. Steers were grazed on ryegrass pastures using set stocking rates of 2.24 steers/ha while being fed corn or corn + corn oil at 1% BW. Forage DMI was reduced by grain supplementation, which allowed forage DM per hectare to remain constant throughout yr 1 of the experiment. Providing additional energy in the form of supplement has often reduced the intake of grazed forage. Chase and Hibberd (1987) fed incremental levels of corn to cows consuming low-quality forage and reported linear
decreases in forage intake. Pordomingo et al. (1991) reported that cattle supplemented with corn while grazing summer pasture in New Mexico had reduced forage intakes. These reports agree with other data from tropical and temperate forages (Minson, 1990). In yr 2, a continued drought (average rainfall for the experimental period = 0.33 cm) decreased forage DM per hectare. However, forage available DM was not different among treatments.
Performance and Carcass Traits Steer supplement DMI on ryegrass had a year × treatment interaction (Table 4). Steer supplement DMI for the 1% corn treatment was higher in yr 1 and DMI was higher for the 1% corn + corn oil treatment in yr 2. Total DMI of forage and supplements was not determined because forage intake was not measured. Assuming that cattle consume DM to meet
their energy requirements (Mertens, 1987), less DM would be required when fat replaces carbohydrates as an energy source in diets (Gagliostro and Chilliard, 1991). Fats may decrease the ruminal fermentation and digestibility of fiber (Palmquist and Jenkins, 1980), contributing to rumen fill and decreasing the rate of passage. Brokaw et al. (2001) observed no changes in DMI when heifers were supplemented with low levels (0.375 g/kg of BW) of vegetable oil while grazing a summer pasture (75% Bromus biebersteinii). Other researchers (Hardin et al., 1989; Hall et al., 1990; Patil et al., 1993) reported reductions in DMI when high-forage diets were supplemented with lipids when hay was used as the forage source. Pavan and Duckett (2007) reported a linear decrease in forage and total DMI as supplemental corn oil intake increased on tall fescue pastures. Steer ADG, HCW, and QG were higher for both treatments (Table 4; 12 = US Choice −) in yr 1. This
Table 3. Available ryegrass DM (kg/ha) in pastures being grazed by finishing steers, yr 2 Item1 February 13 March 3 March 24 April 5 April 24 May 5
Treatment 1, pasture 1
Treatment 1, pasture 2
Treatment 2, pasture 3
Treatment 2, pasture 4
Treatment 3, pasture 5
Treatment 3, pasture 6
Avg of 6 pastures
1,004 717 576 269 807 816
1,363 646 768 1,506 968 816
2,008 1,506 1,025 2,152 1,076 1,009
1,721 1,506 1,281 1,775 1,291 1,225
2,223 1,829 896 2,421 1,183 1,345
1,578 717 1,345 1,560 1,614 1,297
1,650 1,154 982 1,614 1,156 1,085
Each value is the mean of 4 ground-level forage samples. Treatment 1 = grass only; treatment 2 = corn only; treatment 3 = corn + corn oil.
1
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Table 4. Effects of supplementing steers on ryegrass with corn and corn + corn oil on steer performance during yr 1 Treatment Item Steers, no. Steer performance Initial BW, kg Supplement total DMI, kg 83-d ADG, kg Hot carcass weight, kg QG1 YG2
Corn
Corn + corn oil
8
8
422.96 4.63 1.78 347.90 12.27 2.38
424.69 4.33 1.89 354.44 12.61 2.75
SE
P-value
22.41 0.01 0.19 6.95 0.39 0.13
<0.91 <0.03 <0.40 <0.17 <0.55 <0.16
QG: 9 = US Select −; 10 = US Select; 11 = US Select +; 12 = US Choice −; 13 = US Choice.
1
2
YG scale: 1 to 5.
may be attributed to higher steer initial BW for yr 1, which resulted in a corresponding increase in supplement DMI for both treatments in yr 1 because supplement feeding rates were based on a percentage of BW. Animal response to supplementation is thought to be subject to the forage substitution rate (Bargo et al., 2003). During yr 2 of the study, steers grazing only ryegrass had the lowest ADG, HCW, QG, and YG despite having the highest initial
BW (Table 5). Although the main focus of this study was on corn and corn + corn oil supplementation of steers grazing ryegrass pastures, yr 2 data indicate the expected differences in performance, carcass merit, and LCFA of grass-only finishing compared with the 2 supplementation treatments. According to our results, oil-supplemented steers consumed less supplement than steers fed corn, but these steers had similar carcass characteristics and quality compared
with nonsupplemented steers. Allen (2000) reported that the addition of oilseeds and hydrogenated fatty acids (5 to 6% total fatty acids) to diets resulted in a quadratic effect on DMI, with minimums occurring at 3 and 2.3% added fatty acids, respectively. Addition of tallow, grease, or calcium salts of palm fatty acids to diets resulted in a general negative linear decrease in DMI. Smith et al. (1993) reported that ruminally active fats had a greater negative effect on DMI, ruminal fermentation, and digestibility of NDF when diets were high in corn silage than when they were high in alfalfa. Pavan and Duckett (2007) reported that oil-supplemented steers consumed less forage and produced heavier carcasses than nonsupplemented steers with unlimited forage. Supplement conversion rates were improved when forage substitution rates were reduced by lower forage availability (Beretta et al., 2006). Andrae et al. (2000) reported decreased DMI when Angus steers were fed rations containing high-oil corn, regardless of whether the high-oil corn diet was isocaloric with the control or had increased energy density. The increased dietary lipids resulted in an increased marbling score and QG, al-
Table 5. Effects of supplementing steers on ryegrass without and with corn and corn + corn oil on steer performance during yr 2 Treatment Item Steers,1 no. Steer performance Initial BW, kg Supplement total DMI, kg 112-d ADG, kg Supplement total DMI/gain Hot carcass weight, kg QG2 YG3 a,b
No corn 9 414.2 — 1.07a — 288.1a 9.78 1.89
Corn 14 387.6 4.40 1.65b 7.60 321.4b 10.57 2.29
Corn + corn oil
SE
P-value
21.3 0.02 0.20 0.10 16.0 0.43 0.22
<0.04 <0.0015 <0.0001 <0.50 <0.0001 <0.28 <0.10
14 387.8 4.48 1.62b 8.14 326.0b 10.29 2.43
Means within a row bearing different superscript letters are different (P < 0.05).
Originally, 14 steers were assigned to all 3 treatments. Because of forage availability, only 9 steers completed the entire 112-d experimental period for the no corn treatment.
1
2
QG: 9 = US Select −; 10 = US Select; 11 = US Select +; 12 = US Choice −; 13 = US Choice.
3
YG scale: 1 to 5.
Forage-finished beef supplemented with corn and corn oil
though other quality parameters were unaffected (Andrae et al., 2000). In contrast, Engle et al. (2000) observed decreased DMI, marbling, dressing percentage, KPH percentage, YG, LM area, and QG when Angus steers were
fed a high-concentrate diet supplemented with 4.0% soybean oil. A 3-yr study evaluating finishing steer performance on corn silage and small grain pasture resulted in no difference in ADG (Utley et al., 1973).
Table 6. Comparison of long-chain fatty acid composition of longissimus dorsi (LM ) and subcutaneous (SQ) samples from steers finished on ryegrass with either supplemental corn or supplemental corn + corn oil in yr 1 Treatment Item, % of total fatty acids LM fatty acid composition C16:0 C16:1 C14:0 C14:1 C18:0 C18:1 trans-11 C18:1 cis-9 Cis-9, trans-11 Trans-10, cis-12 Total, mg/g MUFA1 SFA2 PUFA3 n-64 n-35 n-6:n-3 SQ fatty acid composition C16:0 C16:1 C14:0 C14:1 C18:0 C18:1 t11 C18:1 c9 Cis-9, trans-11 Trans-10, cis-12 Total, mg/g MUFA SFA PUFA n-6 n-3 n-6:n-3
Corn
Corn + corn oil
SE
P-value
30.36 4.16 3.80 0.85 19.50 2.07 37.76 0.49 0.03 96.14 45.62 55.40 5.39 3.17 3.12 1.08
29.43 3.93 3.42 0.82 15.73 1.67 38.66 0.63 0.04 140.10 45.99 50.25 5.91 3.80 3.68 1.06
0.82 0.22 0.27 0.06 3.26 0.44 1.10 0.11 0.01 4.46 0.88 3.87 0.56 0.26 0.37 0.14
<0.28 <0.31 <0.19 <0.58 <0.27 <0.38 <0.43 <0.23 <0.26 <0.36 <0.68 <0.21 <0.37 <0.03 <0.15 <0.88
29.69 5.69 4.90 1.86 13.26 — 39.09 0.77 0.04 81.98 47.31 49.67 3.50 1.57 1.61 0.98
28.31 5.10 4.16 1.55 13.60 — 40.71 1.15 0.05 77.47 48.03 47.81 4.44 2.12 2.10 1.04
0.55 0.26 0.29 0.16 0.69 — 1.07 0.16 0.01 7.24 1.04 1.05 0.32 0.12 0.16 0.09
<0.03 <0.04 <0.02 <0.08 <0.63 — <0.16 <0.04 <0.22 <0.62 <0.50 <0.10 <0.01 <0.0005 <0.008 <0.54
Monounsaturated fatty acids (MUFA): C14:1, C16:1, C18:1 trans-9, C18:1 trans-12, C18:1 trans-11, C18:1 cis-9, C18:1 cis-11.
1
2
Saturated fatty acids (SFA): C12:0, C13:0, C14:0, C15:0, C16:0, C17:0, C18:0.
PUFA: C18:2n-6, C18:3n-3, cis-9, trans-11 conjugated linoleic acid (CLA), cis-11, trans-13 CLA, trans-10, cis-12 CLA, cis-9, cis-11 CLA, cis-10, cis-12 CLA, C20:4n-6, C205n-3, C22:5n-3, C22:6n-6.
3
4
n-6: C18:2n-6 and C20:4n-6.
5
n-3: C18:3n-3, C20:5n-3, C22:5n-3, C22:6n-6.
591
However, the steers that were fed a corn silage and cottonseed meal diet had lower HCW than steers grazing oat and rye pastures. United States finished beef QG (Prime, Choice, Select, and Standard) are based mostly on the marbling in the ribeye. Carcass prices are based on these grades and decline with decreasing grades. Most finished beef in the United States is graded Low Choice to High Select. In yr 1, of the 16 steers finished on ryegrass pasture with corn or corn + corn oil, 13 carcasses graded US Choice, 4 steers received Certified Angus Beef premiums, and 3 carcasses graded US Select. In yr 2, of the 9 steers finished on ryegrass only, 2 graded US Choice −, 5 graded US Select, and 2 graded US Standard, compared with 14 steers finished on corn, with 4 grading US Choice −, 10 grading US Select, and on corn + corn oil, 2 graded US Choice −, and 12 graded US Select. Ultimately, with improved genetics, higher marbling Angus steers may reach acceptable market weight and QG on foragefinished systems.
Fatty Acid Composition Pasturing animals has a positive effect on concentrations of beneficial fatty acids in beef (Laborde et al., 2002; Rule et al., 2002) while maintaining carcass quality. Generally, forages contain a higher concentration of linolenic acid (C18:3), whereas linoleic acid (C18:2) is the predominant fatty acid in cereal grains and seeds. In a study by Shantha et al. (1997), the top round of grass-fed cattle contained higher concentrations of CLA compared with those supplemented with 8.5 kg of cracked corn. Concentrations of LM fatty acids were not significantly different in yr 1 for both the corn and corn + corn oil treatments (C14:0, C14:1, C16:0, and C16:1; Table 6). Concentrations of several SQ fatty acids were significantly decreased with corn oil supplementation (C14:0, C14:1, C16:0, and C16:1) during yr 1 (Table 6). However, during yr 1, CLA cis-9, trans-11 was significantly higher with
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Table 7. Comparison of long-chain fatty acid composition of longissimus dorsi (LM) and subcutaneous (SQ) samples from steers finished on ryegrass alone, or ryegrass with either supplemental corn or supplemental corn + corn oil in yr 2 Treatment Item, % of total fatty acids LM fatty acid composition C16:0 C16:1 C14:0 C14:1 C18:0 C18:1 t11 C18:1 cis-9 Cis-9, trans-11 Trans-10, cis-12 Total, mg/g MUFA1 SFA2 PUFA3 n-64 n-35 n-6:n-3 SQ fatty acid composition C16:0 C16:1 C14:0 C14:1 C18:0 C18:1 trans-11 C18:1 cis-9 Cis-9, trans-11 Trans-10, cis-12 Total, mg/g MUFA SFA PUFA n-6 n-3 n-6:n-3 a,b
No corn
Corn
Corn + corn oil
SE
P-value
25.82 3.36 2.45 0.65 15.04 2.74a 38.16 0.72 0.04 99.97 45.97 46.65 7.33 3.97 2.39 1.68a
26.40 2.73 2.57 0.66 16.53 2.89a 36.28 0.67 0.08 97.98 45.30 50.12 6.89 4.27 2.29 2.08a
24.83 2.67 2.35 0.64 16.94 4.45b 35.14 0.84 0.02 97.76 45.35 47.46 7.94 5.52 2.25 3.30b
0.67 0.26 0.24 0.11 0.97 0.24 1.29 0.06 0.03 0.57 0.42 1.23 0.47 0.52 0.31 0.50
<0.0934 <0.0775 <0.65 <0.99 <0.1757 <0.0001 <0.0985 <0.028 <0.1439 <0.1049 <0.6628 <0.1530 <0.3055 <0.0237 <0.9426 <0.0028
27.26a 4.80 3.79 1.24 14.12 3.31a 38.82 1.03a 0.012 99.99 50.14 47.00 2.84a 0.98a 0.55 1.77
27.66a 4.58 3.91 1.29 14.33 3.92a 37.75 1.05a 0.007 98.58 48.59 48.70 3.18a 1.31a 0.91 1.85
25.84b 4.16 3.87 1.24 14.38 5.27b 37.76 1.26b 0.009 98.28 49.48 46.49 4.12b 1.99b 1.07 2.87
0.40 0.33 0.20 0.11 0.80 0.22 0.70 0.08 0.002 0.42 0.53 0.54 0.14 0.12 0.20 0.34
<0.0002 <0.2048 <0.8547 <0.8440 <0.9490 <0.0001 <0.3195 <0.0171 <0.0032 <0.0975 <0.2462 <0.0492 <0.0001 <0.0001 <0.1365 <0.0073
Means within a row bearing different superscript letters are different (P < 0.05).
1
Monounsaturated fatty acids (MUFA): C14:1, C16:1, C18:1 trans-9, C18:1 trans-12, C18:1 trans-11, C18:1 cis-9, C18:1 cis-11.
2
Saturated fatty acids (SFA): C12:0, C13:0, C14:0, C15:0, C16:0, C17:0, C18:0.
PUFA: C18:2n-6, C18:3n-3, cis-9trans-11 conjugated linoleic acid (CLA), cis-11, trans-13 CLA, trans-10, cis-12 CLA, cis-9, cis-11 CLA, cis-10, cis-12 CLA, C20:4n-6, C205n-3, C22:5n-3, C22:6n-6.
3
4
n-6: C18:2n-6 and C20:4n-6.
5
n-3: C18:3n-3, C20:5n-3, C22:5n-3, C22:6n-6.
corn oil supplementation. For both years of the experimental period, corn oil supplementation increased concentrations of CLA cis-9, trans-11 and trans-10, cis-12 fatty acids (Table 6 and 7). Steers on the grass only treatment had higher concentrations of C16:1 in LM samples compared
with steers receiving corn and corn + corn oil supplementation within yr 2 (Table 7). French et al. (2000) reported that diets based on pasture or hay supported high amounts of CLA deposition in tissues but that silage did not, which led to the conclusion that dietary use of both oil and the hay or
pasture synergistically increased CLA content of muscle. Pavan et al. (2007) reported an increase in trans vaccenic acid and CLA for corn oil supplementation (0.75 g/kg BW) of steers grazing endophyte-free tall fescue. The effect of increasing dietary linoleic acid through vegetable oil supple-
Forage-finished beef supplemented with corn and corn oil
Table 8. Effects of supplementing steers on ryegrass without and with corn and corn + corn oil on meat tenderness, juiciness, and flavor of longissimus dorsi (LM) steaks in yr 2 Item1 Juiciness Initial tenderness Overall tenderness Beef flavor Off-flavor a,b
No corn
Corn
Corn + corn oil
SE
P-value
4.85 4.71 4.74a 0.37 1.97
5.89 5.76 5.20ab 0.11 2.33
5.60 5.51 5.52b 0.09 1.72
0.51 0.52 0.27 0.15 0.42
<0.17 <0.17 <0.05 <0.18 <0.38
Means within a row bearing different superscript letters are different (P < 0.05).
Line scale number (0 to 8): 0 = none; 1 = extremely dry, tough, or bland; 8 = extremely juicy, tender, or intense.
1
mentation on tissue stearic (C18:0) and oleic (C18:1) acid content has been variable across studies. Pavan et al. (2007) and Andrae et al. (2001) did not observe changes in stearic or oleic acid percentages when feedlot diets containing typical corn were replaced by high-oil corn. Madron et al. (2002) observed an increase in stearic acid and a decrease in oleic acid percentage in LM when extruded full-fat soybeans were included in a high-concentrate diet at increasing levels. In contrast, Gillis et al. (2004) detected similar proportions of stearic acid and lower oleic acid when heifers were fed a high-concentrate diet with 4% corn oil for 60 d. In our study, oleic acid concentrations were significantly decreased in LM with the supplementation of corn oil in yr 1 (Table 6). In LM tissue, stearic acid concentration decreased numerically with corn oil supplementation and decreased for yr 2 (17.71 vs. 16.23; 17.61 vs. 16.33, respectively). In SQ tissue, stearic acid concentration increased numerically with corn oil supplementation and increased for yr 2 (13.82 vs. 13.97; 13.43 vs. 14.36, respectively). Oil supplementation in yr 2 decreased palmitic acid (C16:0; P < 0.01) and numerically decreased myristic acid (C14:0; P > 0.10; Table 6) in SQ samples. Palmitic and myristic acids were numerically decreased in yr 2 in LM samples (P > 0.10; Table 6). Oil supplementation decreased both myristic and palmitic acids to levels numerically lower than
those samples from steers grazing ryegrass only. These fatty acids are considered to have hypercholesterolemic effects on humans. Compared with palmitic and myristic acids, stearic acid is considered neutral with regard to cholesterol levels in humans. In a review examining the regulation of human plasma low-density lipoprotein (LDL) cholesterol concentrations by dietary cholesterol and fatty acids, Spady et al. (1993) concluded that intakes of C14:0 and C16:0 were positively correlated with increased plasma LDL cholesterol and thus were risk factors for cardiac disease. The fatty acids C18:1 cis-9 and linoleic acid tended to decrease plasma LDL cholesterol; stearic acid was neutral in effect. According to this scheme, supplemental corn oil in our study resulted in changes in LCFA in edible tissues that would result in a healthier product. Beaulieu et al. (2002) reported that dietary soybean oil had only modest effects on proportions of the major LCFA in various tissues, in agreement with the conclusions of others (Brandt and Anderson, 1990; Kimura, 1997; Engle et al., 2000) that the LCFA composition of ruminant tissues is relatively insensitive to dietary lipid. An exception to this is when the dietary lipid demonstrates some resistance to ruminal biohydrogenation (Rule et al., 1994; Andrae et al., 2001), illustrating the importance of ruminal biohydrogenation on tissue LCFA. Treatment effects may be more pronounced if
593
imposed during the growing phase. When Angus crossbred steers were finished on pasture or high-concentrate diets, the cis-9, trans-11 content of the loin and round was increased only when the backgrounding ration also included pasture (Poulson et al., 2001). In the present study, steers in yr 1 were backgrounded for a longer time on rye pasture compared with steers in yr 2, possibly contributing to the increase in the CLA isomer cis-9, trans-11 in the LM. Tissue LCFA composition was altered when calves were finished at 6 mo of age rather than at 18 mo (Rule et al., 1997). Cattle diets have affected the sensory properties of beef. Davis et al. (1981) and Berry et al. (1988) reported that sensory ratings for tenderness were higher for grain-fed beef than for forage-finished beef. In some cases, flavor desirability scores were more favorable and off-flavor notes were less common in grain-fed beef (Davis et al., 1981; Berry et al., 1988). In this study, steaks from steers supplemented with corn + corn oil were given higher scores for overall tenderness compared with steaks from steers that grazed ryegrass only in yr 2 (Table 8). Other sensory parameters were not significantly different among treatments during yr 2. Sensory data were not collected during yr 1. The use of improved forages is common and is critical for improving beef cattle production. Either grazing animals on pasture, feeding fresh forages, or increasing the amount of forage in the diet may elevate the percentage of CLA as a proportion of total fatty acids in meat from ruminants. The increase in beef CLA content varies with the quality and quantity of forage consumed by cattle. Corn oil supplementation in grazing steer diets increased the concentration of the CLA isomer cis-9, trans-11 in the LM. Corn oil supplementation tended to increase CLA isomers (cis-9, trans-11 and trans-10, cis-12) in adipose tissue. The increase in cis-9, trans-11 CLA content in beef is not as dramatic as the increase often observed in milk from cows grazed on pasture. This difference results from differences
594
Corriher et al.
in CLA production in the rumen or endogenous synthesis of CLA in the intramuscular fat of beef cattle fed high-forage diets (French et al., 2000).
ACKNOWLEDGMENTS The authors gratefully acknowledge the technical support of Alana Nichols, G. W. Stone, Mike Keeler, Gina McKinney, Pat Smith, and Ryan Crowe, University of Georgia, Animal and Dairy Science Department (Athens, GA, and Tifton, GA).
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Forage-finished beef supplemented with corn and corn oil hydrogenated tallow on feed intake, digestibility, live weight gain, and carcass characteristics. J. Anim. Sci. 71:2284. Pavan, E., and S. K. Duckett. 2007. Corn oil supplementation to steers grazing endophytefree tall fescue. II. Effects on longissimus muscle and subcutaneous adipose fatty acid composition and stearoyl-CoA desaturase activity and expression. J. Anim. Sci. 85:1731. Pavan, E., S. K. Duckett, and J. G. Andrae. 2007. Corn oil supplementation to steers grazing endophyte-free tall fescue. I. Effects on in vivo digestibility, performance, and carcass traits. J. Anim. Sci. 85:1330. Pordomingo, A. J., J. D. Wallace, A. S. Freeman, and M. L. Galyean. 1991. Supplemental corn grain for steers grazing native rangeland during summer. J. Anim. Sci. 69:1678. Poulson, C. S., T. R. Dhiman, D. Cornforth, K. C. Olson, and J. Walters. 2001. Influence of diet on conjugated linoleic acid content of beef. J. Anim. Sci. 79(Suppl. 1):159. (Abstr.). Ritzenthaler, K. L., M. K. McGuire, R. Falen, T. D. Shultz, N. Dasgupta, and M. A. McGuire. 2001. Estimation of conjugated linoleic acid intake by written dietary assessment methodologies underestimates actual
intake evaluated by food duplicate methodology. J. Nutr. 131:1548. Rule, D. C., K. S. Broughton, S. M. Shellito, and G. Maiorano. 2002. Comparison of muscle fatty acid profiles and cholesterol concentrations of bison, beef cattle, elk, and chicken. J. Anim. Sci. 80:1202. Rule, D. C., J. R. Busboom, and C. J. Kercher. 1994. Effect of dietary canola on fatty acid composition of bovine adipose tissue, muscle, kidney, and liver. J. Anim. Sci. 72:2735. Rule, D. C., M. D. MacNeil, and R. E. Short. 1997. Influence of sire growth potential, time on feed, and growing-finishing strategy on cholesterol and fatty acids on the ground carcass and longissimis muscle of beef steers. J. Anim. Sci. 75:1525. SAS Institute. 2003. Statistical Analysis System, Version 9.1. SAS Inst. Inc., Cary, NC. Scollan, N., J. F. Hocquette, K. Nuernberg, D. Dannenberger, I. Richardson, and A. Moloney. 2006. Innovations in beef production systems that enhance the nutritional and health value of beef lipids and their relationship with meat quality. Meat Sci. 74:17. Scollan, N. D., N. J. Choi, E. Kurt, A. V. Fisher, M. Enser, and J. D. Wood. 2001.
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Manipulating the fatty acid composition of muscle and adipose tissue in beef cattle. Br. J. Nutr. 85:115. Shantha, N. C., W. G. Moody, and Z. Tabeidi. 1997. Conjugated linoleic acid concentration in semimembranosus muscle of grass and grain-fed and zeranol-implanted beef cattle. J. Muscle Foods 8:105. Smith, W. A., B. Harris Jr., H. H. VanHorn, and C. J. Wilcox. 1993. Effects of forage type on production of dairy cows supplemented with whole cottonseed, tallow, and yeast. J. Dairy Sci. 76:205. Spady, D.K., L.A. Woollett, and J.M. Dietschy. 1993. Regulation of plasma LDL-cholesterol levels by dietary cholesterol and fatty acids . Annu. Rev. Nutr. 13:355. Utley, P. R., R. S. Lowrey, and W. C. McCormick. 1973. Corn silage and corn silage plus small grain pasture for finishing steers. J. Anim. Sci. 36:423. Van Soest, P. J., J. B. Robertson, B. A. Lewis, and D. E. Akin. 1991. Methods for dietary fiber, neutral detergent fiber, nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 70:3583.
©2009 American Registry of Professional Animal Scientists
Forage-Finished Beef Supplemented with Corn and Corn Oil
V. A. Corriher,*1 G. M. Hill,* T. D. Pringle,† and B. G. Mullinix Jr.‡ *Department of Animal and Dairy Science, University of Georgia, Tifton 31793; †Department of Animal and Dairy Science, University of Georgia, Athens 30602; and ‡Experimental Statistics, Texas A&M University, Lubbock 79403
ABSTRACT Beef steers were finished on ryegrass with corn or corn + corn oil supplementation in a 2-yr experiment to determine effects on performance and conjugated linoleic acid tissue concentration, especially cis-9, trans-11 (c9,t11). Rib steak (longissimus dorsi, LM) and subcutaneous fat (SQ) samples were analyzed for long-chain fatty acid concentrations. Angus and Angus crossbred steers (yr 1, n = 18, initial BW 369.4 ± 29.1 kg; yr 2, n = 48; initial BW 364.1 ± 1.07 kg) were backgrounded on rye pasture for 71 d (ADG 1.78 ± 0.11 kg) and 41 d (ADG 1.24 ± 0.77 kg), respectively, in yr 1 and yr 2. After rye grazing, steers were assigned to ryegrass pastures (cv. Big Daddy; yr 1: 4 pastures, 1.62 ha each; yr 2: 6 pastures, 1.46 ha each) for 83 d in yr 1 and 112 d in yr 2, and fed corn at 1% BW, without or with corn + corn oil (0.075% BW). In yr 1, steer initial BW (n = 16; 424.3 ± 27.83 kg), 83-d ADG (1.78 vs. 1.89 kg), carcass weight (347.9 vs. 354.44 kg), and QG (12.27 vs. 12.61; 12 = US Select +) were similar for corn vs. corn + corn oil treatments. In yr 2, a ryegrass-only treatment was added to the corn and corn + corn oil treatments used in yr 1. Steers (n = 37, 1 Corresponding author: vacorriher@ ag.tamu.edu
initial BW 390.1 kg ± 27.4) assigned to ryegrass only (n = 9), corn (n = 14), or corn + corn oil (n = 14) treatments had respective 112-d ADG of 1.07, 1.65, and 1.62 kg (P < 0.01); carcass weights of 288.1, 321.4, and 326.0 kg (P < 0.01), and QG of 9.78, 10.57, and 10.29 (10 = US Select, P > 0.28). Feeding corn + corn oil decreased supplement intake in yr 1 (P < 0.03), but it did not improve ADG above feeding corn at 1% BW in either year. In yr 1, concentrations of c9,t11 were similar for corn and corn + corn oil in LM, but corn + corn oil had higher (P < 0.04) concentrations in SQ samples. In yr 2, concentration of c9,t11 was highest for LM (P < 0.03) and SQ (P < 0.02) in corn + corn oil compared with similar values for the ryegrass-only and corn treatments. Results indicate that addition of corn oil with corn may increase conjugated linoleic acid in beef steers finished on ryegrass pasture, but may not affect performance or QG. Key words: beef, forage, corn oil supplementation, carcass, fatty acid
INTRODUCTION Conjugated linoleic acid (CLA) is a collective term used to describe one or more positional and geometric isomers of linoleic acid (cis-9, cis-12octadecadienoic acid). Enhancing the
content of the cis-9, trans-11 isomer of CLA has acquired attention in the beef industry because of its anticarcinogenic and antiatherogenic effects (Scollan et al., 2006). Milk and beef represent the major sources of CLA in the human diet (Ritzenthaler et al., 2001). Although CLA are produced in the rumen by incomplete biohydrogenation of dietary C18:2n-6, CLA is also synthesized in adipose tissue and in the mammary gland by desaturation of C18:1 trans-11 (Griinari et al., 2000). Fat supplementation has become a common practice to increase dietary energy density for high-producing dairy cows and finishing steers. Forages and concentrates are the primary sources of lipid in the ruminant diet. Forages typically contain 2 to 3% of the DM of the leaf as lipid. Forages generally contain a higher concentration of linolenic acid (C18:3), whereas linoleic acid (C18:2) is the predominant fatty acid in cereal grains and seeds. Inclusion of plant oils or whole seeds in ruminant rations has been shown in several studies (Scollan et al., 2001; Mir et al., 2002; Noci et al., 2005b) to increase the concentrations of CLA and PUFA in meat. The CLA and n-3 PUFA concentrations in tissue are relatively high in pasture-fed beef cattle (French et al.,
Forage-finished beef supplemented with corn and corn oil
2000; Engle and Spears, 2004; Noci et al., 2005a). Pavan et al. (2007) reported increased vaccenic acid and CLA concentrations when steers grazing endophyte-free tall fescue were supplemented with corn oil at 0.75 g/kg BW. In that study, the cis-9, trans-11 isomer of CLA was increased when corn oil was supplemented to grazing steers. Feeding higher levels of forage in finishing diets appears to alter the ruminal biohydrogenation of linoleic acid, resulting in greater outflow of intermediates via the trans-11 pathway. Therefore, our objective was to determine the effect of corn oil supplementation on performance and carcass quality in steers finished on ryegrass pasture.
MATERIALS AND METHODS The 2-yr grazing experiment was conducted at The University of Georgia Tifton Beef Unit (Tifton, GA) between February and May 2007 and 2008. Steers for both years were implanted with Component (trenbolone acetate, estradiol, and tylosin tartrate; Ivy Animal Health, Overland Park, KS) on d 1 of each experiment. All cattle were managed under procedures approved by the University
of Georgia Institutional Animal Care and Use Committee.
Backgrounding of Steers During preliminary beef steer growing periods (yr 1 = 71 d; n = 18; yr 2 = 48 d; n = 48), steer yr 1 initial BW was 369.4 ± 29.1 kg, yr 2 initial BW was 364.09 ± 1.07 kg, and their age was 18 mo for yr 1 and 15 mo for yr 2. Steers were either Angus or Angus-crossbred steers; stocked at 2.0 steers/ha, they grazed rye pasture and had ADG of 1.78 ± 0.11 kg for yr 1 and ADG of 1.24 ± 0.77 kg for yr 2. Pastures (yr 1: 4 total pastures, 1.62 ha each; yr 2: 6 total pastures, 1.46 ha each) were harrowed September 21, 2006, and August 30, 2007, and drilled with Wrens Abruzzi Rye (Southern States Cooperative Inc., Richmond, VA) on October 28, 2006, and September 26, 2007, at 1.31 to 1.74 hectaliters/ha.
Grazing Experiment After rye grazing, beef steers (yr 1: n = 16, initial BW 424.3 ± 27.8 kg, age 18 mo; yr 2: n = 37, initial BW 390.1 ± 27.4 kg, age 15 mo; Angus and Angus-crossbred; stocking rate 2.24 head/ha) were fed ground corn
Table 1. Mean DM chemical and fatty acid composition of the different dietary components for steers grazing ryegrass pastures Item Component, % (DM basis) DM CP NDF ADF Total fatty acids, % Fatty acid, % of total C14:0 C16:0 C18:0 C18:1 C18:2 C18:3 Others1 Unidentified 1
Forage
Corn
Corn oil
Corn + corn oil
20 19.1 48.3 29.6 1.19
89.1 11.8 8.0 2.9 3.78
— — — — 91.9
73.5 8.9 7.6 3.0 5.17
0.4 14.6 1.2 1.7 10.6 68.4 1.7 1.4
0.07 13.36 2.31 23.10 54.06 1.30 0.67 0.0
<0.1 10.8 1.96 28.5 55.7 1.3 0.75 0.95
0 10.59 1.96 27.27 57.47 0.97 1.34 0.22
Sum of C12:0, C15:0, C16:1, C17:0, C20:0, C21:0, and C22:0.
587
supplement (1% BW; Rumensin 200 mg/d, Eli Lilly & Co., Indianapolis, IN, supplied by W. B. Fleming Co., Tifton, GA; Table 1) without and with corn oil (0.075% BW) while grazing ryegrass pastures. Grazing was initiated after the establishment of ryegrass, and grazing was terminated at the end of the finishing period (typically 90 to 180 d). During yr 2, three treatments were used; negative control treatment steers grazed ryegrass only, and supplement treatment steers grazed ryegrass and were fed ground corn at 1% BW, without or with corn oil (0.075% BW). In yr 2, seven steers per pasture were initially assigned; however, ryegrass pastures could not sustain this stocking rate for the duration of the 112-d feeding interval. Initial BW was equalized for all 6 groups in initial assignments to 6 groups, which were randomly assigned to 3 treatments with 2 replicate pastures for each group. Ryegrass pastures (cv. Big Daddy; yr 1: 4 paddocks, 1.62 ha each; yr 2: 6 paddocks, 1.46 ha each) were fertilized with a blended fertilizer (24-6-12, N-P2O5-K2O, at 280 kg/ ha, on November 27, 2006, January 11, 2007, March 7, 2007, October 23, 2007, and February 21, 2008). Steers were ranked by BW and randomly assigned to dietary treatments for 83 d in yr 1 and for 112 d in yr 2. Supplements were fed free choice daily at 0800 h. Supplement refusals were weighed daily to determine intake. Initially, 42 steers were assigned to the 3 treatments in yr 2. However, only a total of 37 steers completed the experimental period. After 6 wk of the experimental period, the stocking rate was reduced for grazingonly treatments because of a decline in forage mass. At 14-d intervals beginning in February, forage mass was estimated using a double sampling procedure. Four quadrats (0.1 m2) were clipped to ground level in each paddock and clipped samples were oven-dried. Pooled estimates of DM production were converted to a moisture-free basis using pooled DM values. Steers were weighed at 28-d intervals, and initial and final BW
588 were means of consecutive daily full weights. A commercial mineral [NaCl (maximum) 22.0%; Ca (maximum) 16.0%; P (minimum) 6.5%; Mg (minimum) 1.00%; Cu (minimum) 0.025%; Zn (minimum) 0.25%; Se (minimum) 0.0013%; Beef Cattle High Gain-B, W. B. Fleming Co.] was provided free choice along with water in all paddocks in yr 1. In yr 1, Rumensin was mixed with the corn that was fed to the steers. In yr 2, one treatment was ryegrass only; therefore, a mineral supplying an ionophore (Bovatec) was fed in the mineral supplement (Beef Cattle High Gain-B, W. B. Fleming Co.) along with water in each paddock.
Chemical and Fatty Acid Composition Analysis Forage and corn grain samples were lyophilized, ground through a Wiley mill (Arthur H. Thomas, Philadelphia, PA) equipped with a 1-mm screen, and stored at −20°C for subsequent analysis of OM, NDF, ADF, CP, total fatty acid percentage, and fatty acid profile. Organic matter was measured as the weight loss after combustion for 8 h at 500°C. The NDF and ADF were sequentially determined using an Ankom 200 fiber extractor (Ankom Technologies, Fairport, NY) according to the method of Van Soest et al. (1991). Crude protein concentration was determined by the combustion method with a Leco FP-2000 N analyzer (Leco Corp., St. Joseph, MI). Total fatty acid percentage and fatty acid profile were also determined for corn oil samples. Steers for both years were transported (1,609 km) to Cargill Taylor Beef (Wyalusing, PA) for slaughter. Rib sections were collected from each steer and shipped to The University of Georgia Meat Science and Technology Center in Athens. Samples of subcutaneous (SQ) adipose tissue and a 2.5-cm LM steak, which corresponded to a ribeye steak, were removed from the sections at the 13th rib. A second 2.5-cm LM steak from each carcass was frozen for subsequent sensory evaluations. Both SQ and LM sam-
Corriher et al.
ples from each carcass were stored at −20°C, and before analysis, samples were pulverized in liquid nitrogen. Total lipids were extracted in duplicate from LM and SQ samples according to the procedures of Folch et al. (1957). Lipid extracts from SQ and LM samples were stored at −80°C for subsequent fatty acid determination. For wet tissue lipids, 1 g of ground muscle tissue or 0.4 g of ground SQ fat was extracted. The SQ and LM lipid extracts, containing approximately 2 mg of total lipids, based on the calculated percentage of lipids on a wet tissue basis, were transmethylated (Park and Goins, 1994). Fatty acid methyl esters were analyzed using an HP6850 gas chromatograph (Hewlett-Packard, San Fernando, CA) equipped with an HP7673A automatic sampler (Hewlett-Packard). Separations were accomplished using a 100-m Sp2560 capillary column (0.25 mm i.d. and 0.20-μm film thickness; Supelco, Bellefonte, PA) according to the method of Duckett et al. (2002). Column oven temperature increased from 150 to 160°C at 1°C per min, from 160 to 167°C at 0.2°C per min, from 167 to 225°C at 1.5°C per min, and was then held at 225°C for 16 min. The injector and detector temperatures were maintained at 250°C. Sample injection volume was 1 μL. Hydrogen was the carrier gas at a flow rate of 1 mL/min. Individual fatty acids were identified by comparison of retention times with standards (Sigma, St. Louis, MO; Supelco; Matreya, Pleasant Gap, PA). The fatty acids were quantified by incorporating an internal standard, methyl heptacosanoic acid (C27:0), into each sample during methylation and were expressed as grams per 100 g of tissue. The fatty acid compositions of forage, corn oil, and corn grain were determined by direct transmethylation of lyophilized samples according to the method of Park and Goins (1994) and were analyzed as SQ and intramuscular fatty acid methyl esters.
Palatability Measurements In yr 2, steaks were stored frozen until thawed and prepared for sensory evaluations. For the trained sensory evaluations, the steaks were thawed overnight at 4°C and broiled (model 450N Open-Hearth Broiler, Farberware, Bronx, NY) to an internal end point of 70°C (American Meat Science Association, 1995). Internal temperature was monitored by copper-constantan thermocouples (Omega Engineering, Stamford, CT) placed in the approximate geometric center of each steak. The steaks were served warm to an 8-member trained panel. The panel evaluated juiciness (1 = extremely dry to 8 = extremely juicy), flavor intensity (1 = extremely bland to 8 = extremely intense), overall tenderness (1 = extremely tough to 8 = extremely tender), amount of detectable connective tissue amount (1 = extremely abundant amount to 8 = none detected), and off-flavor (1 = extreme off-flavor to 6 = none detected).
Statistical Analyses Intake, BW gain, carcass variables, and long-chain fatty acid (LCFA) analyses were statistically analyzed as a completely randomized design using the MIXED procedure (SAS Institute, 2003) with pen of cattle as the experimental unit as a random effect and dietary treatment as a fixed effect. Treatment means were compared using the Satterthwaite test (SAS Institute, 2003). Year means were compared for corn and corn + corn oil treatments using the Satterthwaite test (SAS Institute, 2003). Least squares means are presented for main effects when interactions were not significant (P > 0.10); in addition, treatment means for the individual factors are presented in tables.
RESULTS AND DISCUSSION Grazing Experiment Pasture Quality. Forage available DM for both years of the study
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Table 2. Available ryegrass DM (kg/ha) in pastures being grazed by finishing steers, yr 1 Item1 February 9 March 7 March 23 April 6 April 20 1
Treatment 2, pasture 1
Treatment 2, pasture 4
Treatment 3, pasture 2
Treatment 3, pasture 3
Avg of 4 pastures
937 1,169 924 1,205 1,617
867 1,199 1,226 1,435 1,864
818 1,178 1,002 1,377 1,284
890 1,534 1,158 1,511 1,300
878 1,270 1,078 1,382 1,516
Each value is the mean of 4 ground-level forage samples. Treatment 2 = corn only; treatment 3 = corn + corn oil.
averaged 1,251.2 ± 258 kg/ha during the finishing period from January to May. Ryegrass DM availability was not different among treatments, years, or sampling dates (P > 0.10; Tables 2 and 3). Average DM production tended to increase during the experimental period as the grazing season advanced from winter to spring. Therefore, forage availability was not a limiting factor. Early rainfall and drought following the finishing interval during yr 1 contributed to the trend for increasing DM production. Steers were grazed on ryegrass pastures using set stocking rates of 2.24 steers/ha while being fed corn or corn + corn oil at 1% BW. Forage DMI was reduced by grain supplementation, which allowed forage DM per hectare to remain constant throughout yr 1 of the experiment. Providing additional energy in the form of supplement has often reduced the intake of grazed forage. Chase and Hibberd (1987) fed incremental levels of corn to cows consuming low-quality forage and reported linear
decreases in forage intake. Pordomingo et al. (1991) reported that cattle supplemented with corn while grazing summer pasture in New Mexico had reduced forage intakes. These reports agree with other data from tropical and temperate forages (Minson, 1990). In yr 2, a continued drought (average rainfall for the experimental period = 0.33 cm) decreased forage DM per hectare. However, forage available DM was not different among treatments.
Performance and Carcass Traits Steer supplement DMI on ryegrass had a year × treatment interaction (Table 4). Steer supplement DMI for the 1% corn treatment was higher in yr 1 and DMI was higher for the 1% corn + corn oil treatment in yr 2. Total DMI of forage and supplements was not determined because forage intake was not measured. Assuming that cattle consume DM to meet
their energy requirements (Mertens, 1987), less DM would be required when fat replaces carbohydrates as an energy source in diets (Gagliostro and Chilliard, 1991). Fats may decrease the ruminal fermentation and digestibility of fiber (Palmquist and Jenkins, 1980), contributing to rumen fill and decreasing the rate of passage. Brokaw et al. (2001) observed no changes in DMI when heifers were supplemented with low levels (0.375 g/kg of BW) of vegetable oil while grazing a summer pasture (75% Bromus biebersteinii). Other researchers (Hardin et al., 1989; Hall et al., 1990; Patil et al., 1993) reported reductions in DMI when high-forage diets were supplemented with lipids when hay was used as the forage source. Pavan and Duckett (2007) reported a linear decrease in forage and total DMI as supplemental corn oil intake increased on tall fescue pastures. Steer ADG, HCW, and QG were higher for both treatments (Table 4; 12 = US Choice −) in yr 1. This
Table 3. Available ryegrass DM (kg/ha) in pastures being grazed by finishing steers, yr 2 Item1 February 13 March 3 March 24 April 5 April 24 May 5
Treatment 1, pasture 1
Treatment 1, pasture 2
Treatment 2, pasture 3
Treatment 2, pasture 4
Treatment 3, pasture 5
Treatment 3, pasture 6
Avg of 6 pastures
1,004 717 576 269 807 816
1,363 646 768 1,506 968 816
2,008 1,506 1,025 2,152 1,076 1,009
1,721 1,506 1,281 1,775 1,291 1,225
2,223 1,829 896 2,421 1,183 1,345
1,578 717 1,345 1,560 1,614 1,297
1,650 1,154 982 1,614 1,156 1,085
Each value is the mean of 4 ground-level forage samples. Treatment 1 = grass only; treatment 2 = corn only; treatment 3 = corn + corn oil.
1
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Table 4. Effects of supplementing steers on ryegrass with corn and corn + corn oil on steer performance during yr 1 Treatment Item Steers, no. Steer performance Initial BW, kg Supplement total DMI, kg 83-d ADG, kg Hot carcass weight, kg QG1 YG2
Corn
Corn + corn oil
8
8
422.96 4.63 1.78 347.90 12.27 2.38
424.69 4.33 1.89 354.44 12.61 2.75
SE
P-value
22.41 0.01 0.19 6.95 0.39 0.13
<0.91 <0.03 <0.40 <0.17 <0.55 <0.16
QG: 9 = US Select −; 10 = US Select; 11 = US Select +; 12 = US Choice −; 13 = US Choice.
1
2
YG scale: 1 to 5.
may be attributed to higher steer initial BW for yr 1, which resulted in a corresponding increase in supplement DMI for both treatments in yr 1 because supplement feeding rates were based on a percentage of BW. Animal response to supplementation is thought to be subject to the forage substitution rate (Bargo et al., 2003). During yr 2 of the study, steers grazing only ryegrass had the lowest ADG, HCW, QG, and YG despite having the highest initial
BW (Table 5). Although the main focus of this study was on corn and corn + corn oil supplementation of steers grazing ryegrass pastures, yr 2 data indicate the expected differences in performance, carcass merit, and LCFA of grass-only finishing compared with the 2 supplementation treatments. According to our results, oil-supplemented steers consumed less supplement than steers fed corn, but these steers had similar carcass characteristics and quality compared
with nonsupplemented steers. Allen (2000) reported that the addition of oilseeds and hydrogenated fatty acids (5 to 6% total fatty acids) to diets resulted in a quadratic effect on DMI, with minimums occurring at 3 and 2.3% added fatty acids, respectively. Addition of tallow, grease, or calcium salts of palm fatty acids to diets resulted in a general negative linear decrease in DMI. Smith et al. (1993) reported that ruminally active fats had a greater negative effect on DMI, ruminal fermentation, and digestibility of NDF when diets were high in corn silage than when they were high in alfalfa. Pavan and Duckett (2007) reported that oil-supplemented steers consumed less forage and produced heavier carcasses than nonsupplemented steers with unlimited forage. Supplement conversion rates were improved when forage substitution rates were reduced by lower forage availability (Beretta et al., 2006). Andrae et al. (2000) reported decreased DMI when Angus steers were fed rations containing high-oil corn, regardless of whether the high-oil corn diet was isocaloric with the control or had increased energy density. The increased dietary lipids resulted in an increased marbling score and QG, al-
Table 5. Effects of supplementing steers on ryegrass without and with corn and corn + corn oil on steer performance during yr 2 Treatment Item Steers,1 no. Steer performance Initial BW, kg Supplement total DMI, kg 112-d ADG, kg Supplement total DMI/gain Hot carcass weight, kg QG2 YG3 a,b
No corn 9 414.2 — 1.07a — 288.1a 9.78 1.89
Corn 14 387.6 4.40 1.65b 7.60 321.4b 10.57 2.29
Corn + corn oil
SE
P-value
21.3 0.02 0.20 0.10 16.0 0.43 0.22
<0.04 <0.0015 <0.0001 <0.50 <0.0001 <0.28 <0.10
14 387.8 4.48 1.62b 8.14 326.0b 10.29 2.43
Means within a row bearing different superscript letters are different (P < 0.05).
Originally, 14 steers were assigned to all 3 treatments. Because of forage availability, only 9 steers completed the entire 112-d experimental period for the no corn treatment.
1
2
QG: 9 = US Select −; 10 = US Select; 11 = US Select +; 12 = US Choice −; 13 = US Choice.
3
YG scale: 1 to 5.
Forage-finished beef supplemented with corn and corn oil
though other quality parameters were unaffected (Andrae et al., 2000). In contrast, Engle et al. (2000) observed decreased DMI, marbling, dressing percentage, KPH percentage, YG, LM area, and QG when Angus steers were
fed a high-concentrate diet supplemented with 4.0% soybean oil. A 3-yr study evaluating finishing steer performance on corn silage and small grain pasture resulted in no difference in ADG (Utley et al., 1973).
Table 6. Comparison of long-chain fatty acid composition of longissimus dorsi (LM ) and subcutaneous (SQ) samples from steers finished on ryegrass with either supplemental corn or supplemental corn + corn oil in yr 1 Treatment Item, % of total fatty acids LM fatty acid composition C16:0 C16:1 C14:0 C14:1 C18:0 C18:1 trans-11 C18:1 cis-9 Cis-9, trans-11 Trans-10, cis-12 Total, mg/g MUFA1 SFA2 PUFA3 n-64 n-35 n-6:n-3 SQ fatty acid composition C16:0 C16:1 C14:0 C14:1 C18:0 C18:1 t11 C18:1 c9 Cis-9, trans-11 Trans-10, cis-12 Total, mg/g MUFA SFA PUFA n-6 n-3 n-6:n-3
Corn
Corn + corn oil
SE
P-value
30.36 4.16 3.80 0.85 19.50 2.07 37.76 0.49 0.03 96.14 45.62 55.40 5.39 3.17 3.12 1.08
29.43 3.93 3.42 0.82 15.73 1.67 38.66 0.63 0.04 140.10 45.99 50.25 5.91 3.80 3.68 1.06
0.82 0.22 0.27 0.06 3.26 0.44 1.10 0.11 0.01 4.46 0.88 3.87 0.56 0.26 0.37 0.14
<0.28 <0.31 <0.19 <0.58 <0.27 <0.38 <0.43 <0.23 <0.26 <0.36 <0.68 <0.21 <0.37 <0.03 <0.15 <0.88
29.69 5.69 4.90 1.86 13.26 — 39.09 0.77 0.04 81.98 47.31 49.67 3.50 1.57 1.61 0.98
28.31 5.10 4.16 1.55 13.60 — 40.71 1.15 0.05 77.47 48.03 47.81 4.44 2.12 2.10 1.04
0.55 0.26 0.29 0.16 0.69 — 1.07 0.16 0.01 7.24 1.04 1.05 0.32 0.12 0.16 0.09
<0.03 <0.04 <0.02 <0.08 <0.63 — <0.16 <0.04 <0.22 <0.62 <0.50 <0.10 <0.01 <0.0005 <0.008 <0.54
Monounsaturated fatty acids (MUFA): C14:1, C16:1, C18:1 trans-9, C18:1 trans-12, C18:1 trans-11, C18:1 cis-9, C18:1 cis-11.
1
2
Saturated fatty acids (SFA): C12:0, C13:0, C14:0, C15:0, C16:0, C17:0, C18:0.
PUFA: C18:2n-6, C18:3n-3, cis-9, trans-11 conjugated linoleic acid (CLA), cis-11, trans-13 CLA, trans-10, cis-12 CLA, cis-9, cis-11 CLA, cis-10, cis-12 CLA, C20:4n-6, C205n-3, C22:5n-3, C22:6n-6.
3
4
n-6: C18:2n-6 and C20:4n-6.
5
n-3: C18:3n-3, C20:5n-3, C22:5n-3, C22:6n-6.
591
However, the steers that were fed a corn silage and cottonseed meal diet had lower HCW than steers grazing oat and rye pastures. United States finished beef QG (Prime, Choice, Select, and Standard) are based mostly on the marbling in the ribeye. Carcass prices are based on these grades and decline with decreasing grades. Most finished beef in the United States is graded Low Choice to High Select. In yr 1, of the 16 steers finished on ryegrass pasture with corn or corn + corn oil, 13 carcasses graded US Choice, 4 steers received Certified Angus Beef premiums, and 3 carcasses graded US Select. In yr 2, of the 9 steers finished on ryegrass only, 2 graded US Choice −, 5 graded US Select, and 2 graded US Standard, compared with 14 steers finished on corn, with 4 grading US Choice −, 10 grading US Select, and on corn + corn oil, 2 graded US Choice −, and 12 graded US Select. Ultimately, with improved genetics, higher marbling Angus steers may reach acceptable market weight and QG on foragefinished systems.
Fatty Acid Composition Pasturing animals has a positive effect on concentrations of beneficial fatty acids in beef (Laborde et al., 2002; Rule et al., 2002) while maintaining carcass quality. Generally, forages contain a higher concentration of linolenic acid (C18:3), whereas linoleic acid (C18:2) is the predominant fatty acid in cereal grains and seeds. In a study by Shantha et al. (1997), the top round of grass-fed cattle contained higher concentrations of CLA compared with those supplemented with 8.5 kg of cracked corn. Concentrations of LM fatty acids were not significantly different in yr 1 for both the corn and corn + corn oil treatments (C14:0, C14:1, C16:0, and C16:1; Table 6). Concentrations of several SQ fatty acids were significantly decreased with corn oil supplementation (C14:0, C14:1, C16:0, and C16:1) during yr 1 (Table 6). However, during yr 1, CLA cis-9, trans-11 was significantly higher with
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Table 7. Comparison of long-chain fatty acid composition of longissimus dorsi (LM) and subcutaneous (SQ) samples from steers finished on ryegrass alone, or ryegrass with either supplemental corn or supplemental corn + corn oil in yr 2 Treatment Item, % of total fatty acids LM fatty acid composition C16:0 C16:1 C14:0 C14:1 C18:0 C18:1 t11 C18:1 cis-9 Cis-9, trans-11 Trans-10, cis-12 Total, mg/g MUFA1 SFA2 PUFA3 n-64 n-35 n-6:n-3 SQ fatty acid composition C16:0 C16:1 C14:0 C14:1 C18:0 C18:1 trans-11 C18:1 cis-9 Cis-9, trans-11 Trans-10, cis-12 Total, mg/g MUFA SFA PUFA n-6 n-3 n-6:n-3 a,b
No corn
Corn
Corn + corn oil
SE
P-value
25.82 3.36 2.45 0.65 15.04 2.74a 38.16 0.72 0.04 99.97 45.97 46.65 7.33 3.97 2.39 1.68a
26.40 2.73 2.57 0.66 16.53 2.89a 36.28 0.67 0.08 97.98 45.30 50.12 6.89 4.27 2.29 2.08a
24.83 2.67 2.35 0.64 16.94 4.45b 35.14 0.84 0.02 97.76 45.35 47.46 7.94 5.52 2.25 3.30b
0.67 0.26 0.24 0.11 0.97 0.24 1.29 0.06 0.03 0.57 0.42 1.23 0.47 0.52 0.31 0.50
<0.0934 <0.0775 <0.65 <0.99 <0.1757 <0.0001 <0.0985 <0.028 <0.1439 <0.1049 <0.6628 <0.1530 <0.3055 <0.0237 <0.9426 <0.0028
27.26a 4.80 3.79 1.24 14.12 3.31a 38.82 1.03a 0.012 99.99 50.14 47.00 2.84a 0.98a 0.55 1.77
27.66a 4.58 3.91 1.29 14.33 3.92a 37.75 1.05a 0.007 98.58 48.59 48.70 3.18a 1.31a 0.91 1.85
25.84b 4.16 3.87 1.24 14.38 5.27b 37.76 1.26b 0.009 98.28 49.48 46.49 4.12b 1.99b 1.07 2.87
0.40 0.33 0.20 0.11 0.80 0.22 0.70 0.08 0.002 0.42 0.53 0.54 0.14 0.12 0.20 0.34
<0.0002 <0.2048 <0.8547 <0.8440 <0.9490 <0.0001 <0.3195 <0.0171 <0.0032 <0.0975 <0.2462 <0.0492 <0.0001 <0.0001 <0.1365 <0.0073
Means within a row bearing different superscript letters are different (P < 0.05).
1
Monounsaturated fatty acids (MUFA): C14:1, C16:1, C18:1 trans-9, C18:1 trans-12, C18:1 trans-11, C18:1 cis-9, C18:1 cis-11.
2
Saturated fatty acids (SFA): C12:0, C13:0, C14:0, C15:0, C16:0, C17:0, C18:0.
PUFA: C18:2n-6, C18:3n-3, cis-9trans-11 conjugated linoleic acid (CLA), cis-11, trans-13 CLA, trans-10, cis-12 CLA, cis-9, cis-11 CLA, cis-10, cis-12 CLA, C20:4n-6, C205n-3, C22:5n-3, C22:6n-6.
3
4
n-6: C18:2n-6 and C20:4n-6.
5
n-3: C18:3n-3, C20:5n-3, C22:5n-3, C22:6n-6.
corn oil supplementation. For both years of the experimental period, corn oil supplementation increased concentrations of CLA cis-9, trans-11 and trans-10, cis-12 fatty acids (Table 6 and 7). Steers on the grass only treatment had higher concentrations of C16:1 in LM samples compared
with steers receiving corn and corn + corn oil supplementation within yr 2 (Table 7). French et al. (2000) reported that diets based on pasture or hay supported high amounts of CLA deposition in tissues but that silage did not, which led to the conclusion that dietary use of both oil and the hay or
pasture synergistically increased CLA content of muscle. Pavan et al. (2007) reported an increase in trans vaccenic acid and CLA for corn oil supplementation (0.75 g/kg BW) of steers grazing endophyte-free tall fescue. The effect of increasing dietary linoleic acid through vegetable oil supple-
Forage-finished beef supplemented with corn and corn oil
Table 8. Effects of supplementing steers on ryegrass without and with corn and corn + corn oil on meat tenderness, juiciness, and flavor of longissimus dorsi (LM) steaks in yr 2 Item1 Juiciness Initial tenderness Overall tenderness Beef flavor Off-flavor a,b
No corn
Corn
Corn + corn oil
SE
P-value
4.85 4.71 4.74a 0.37 1.97
5.89 5.76 5.20ab 0.11 2.33
5.60 5.51 5.52b 0.09 1.72
0.51 0.52 0.27 0.15 0.42
<0.17 <0.17 <0.05 <0.18 <0.38
Means within a row bearing different superscript letters are different (P < 0.05).
Line scale number (0 to 8): 0 = none; 1 = extremely dry, tough, or bland; 8 = extremely juicy, tender, or intense.
1
mentation on tissue stearic (C18:0) and oleic (C18:1) acid content has been variable across studies. Pavan et al. (2007) and Andrae et al. (2001) did not observe changes in stearic or oleic acid percentages when feedlot diets containing typical corn were replaced by high-oil corn. Madron et al. (2002) observed an increase in stearic acid and a decrease in oleic acid percentage in LM when extruded full-fat soybeans were included in a high-concentrate diet at increasing levels. In contrast, Gillis et al. (2004) detected similar proportions of stearic acid and lower oleic acid when heifers were fed a high-concentrate diet with 4% corn oil for 60 d. In our study, oleic acid concentrations were significantly decreased in LM with the supplementation of corn oil in yr 1 (Table 6). In LM tissue, stearic acid concentration decreased numerically with corn oil supplementation and decreased for yr 2 (17.71 vs. 16.23; 17.61 vs. 16.33, respectively). In SQ tissue, stearic acid concentration increased numerically with corn oil supplementation and increased for yr 2 (13.82 vs. 13.97; 13.43 vs. 14.36, respectively). Oil supplementation in yr 2 decreased palmitic acid (C16:0; P < 0.01) and numerically decreased myristic acid (C14:0; P > 0.10; Table 6) in SQ samples. Palmitic and myristic acids were numerically decreased in yr 2 in LM samples (P > 0.10; Table 6). Oil supplementation decreased both myristic and palmitic acids to levels numerically lower than
those samples from steers grazing ryegrass only. These fatty acids are considered to have hypercholesterolemic effects on humans. Compared with palmitic and myristic acids, stearic acid is considered neutral with regard to cholesterol levels in humans. In a review examining the regulation of human plasma low-density lipoprotein (LDL) cholesterol concentrations by dietary cholesterol and fatty acids, Spady et al. (1993) concluded that intakes of C14:0 and C16:0 were positively correlated with increased plasma LDL cholesterol and thus were risk factors for cardiac disease. The fatty acids C18:1 cis-9 and linoleic acid tended to decrease plasma LDL cholesterol; stearic acid was neutral in effect. According to this scheme, supplemental corn oil in our study resulted in changes in LCFA in edible tissues that would result in a healthier product. Beaulieu et al. (2002) reported that dietary soybean oil had only modest effects on proportions of the major LCFA in various tissues, in agreement with the conclusions of others (Brandt and Anderson, 1990; Kimura, 1997; Engle et al., 2000) that the LCFA composition of ruminant tissues is relatively insensitive to dietary lipid. An exception to this is when the dietary lipid demonstrates some resistance to ruminal biohydrogenation (Rule et al., 1994; Andrae et al., 2001), illustrating the importance of ruminal biohydrogenation on tissue LCFA. Treatment effects may be more pronounced if
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imposed during the growing phase. When Angus crossbred steers were finished on pasture or high-concentrate diets, the cis-9, trans-11 content of the loin and round was increased only when the backgrounding ration also included pasture (Poulson et al., 2001). In the present study, steers in yr 1 were backgrounded for a longer time on rye pasture compared with steers in yr 2, possibly contributing to the increase in the CLA isomer cis-9, trans-11 in the LM. Tissue LCFA composition was altered when calves were finished at 6 mo of age rather than at 18 mo (Rule et al., 1997). Cattle diets have affected the sensory properties of beef. Davis et al. (1981) and Berry et al. (1988) reported that sensory ratings for tenderness were higher for grain-fed beef than for forage-finished beef. In some cases, flavor desirability scores were more favorable and off-flavor notes were less common in grain-fed beef (Davis et al., 1981; Berry et al., 1988). In this study, steaks from steers supplemented with corn + corn oil were given higher scores for overall tenderness compared with steaks from steers that grazed ryegrass only in yr 2 (Table 8). Other sensory parameters were not significantly different among treatments during yr 2. Sensory data were not collected during yr 1. The use of improved forages is common and is critical for improving beef cattle production. Either grazing animals on pasture, feeding fresh forages, or increasing the amount of forage in the diet may elevate the percentage of CLA as a proportion of total fatty acids in meat from ruminants. The increase in beef CLA content varies with the quality and quantity of forage consumed by cattle. Corn oil supplementation in grazing steer diets increased the concentration of the CLA isomer cis-9, trans-11 in the LM. Corn oil supplementation tended to increase CLA isomers (cis-9, trans-11 and trans-10, cis-12) in adipose tissue. The increase in cis-9, trans-11 CLA content in beef is not as dramatic as the increase often observed in milk from cows grazed on pasture. This difference results from differences
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in CLA production in the rumen or endogenous synthesis of CLA in the intramuscular fat of beef cattle fed high-forage diets (French et al., 2000).
ACKNOWLEDGMENTS The authors gratefully acknowledge the technical support of Alana Nichols, G. W. Stone, Mike Keeler, Gina McKinney, Pat Smith, and Ryan Crowe, University of Georgia, Animal and Dairy Science Department (Athens, GA, and Tifton, GA).
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