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,3
* Department of Animal Science, University of Nebraska, Lincoln 68583-0908;
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Department of Animal Science, University of Illinois, Urbana, IL 61801; and
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Monsanto Company, St. Louis, MO 63167
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Key Words: Animal Nutrition • Cattle • Finishing • Maize • Transgenic Plants
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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). Genetic engineering is one form of biotechnology that is used to enhance the agronomic characteristics of plants by inserting a gene or sequence of genes that express desirable traits. Modern use of genetically engineered crops has increased substantially. Between 1998 and 1999, the usage of genetically enhanced crops increased 44% globally (27.8 vs. 39.9 million ha; Clark and Ipharraguerre, 2001). Soybean acres planted that were genetically enhanced were 68% and 75% in 2001 and 2002, respectively, while corn acres planted as genetically enhanced crops increased from 26% to 34% for those years in the United States (USDA, 2002).
Glyphosate is a commercial herbicide that inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase, which plays an important role in the shikimate acid pathway that synthesizes essential aromatic amino acids required for plant growth (Steinrücken and Amrhein, 1980). Few data exist on the effect of feeding Roundup Ready corn to livestock. Because the majority of transgenic corn is fed to livestock, the nutritional quality along with agronomic value must be assessed.
The hypothesis was that feedlot cattle fed Roundup Ready corn will perform similar to cattle fed nontransgenic corn (i.e., the nutritional quality of corn is not changed as a result of Roundup Ready technology). The objective of this research was to compare growth performance and carcass characteristics of finishing steers fed Roundup Ready corn (event GA21 and nk603) to their near-isogenic control hybrid and two reference (nontransgenic) hybrids.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Steers used in these experiments were managed according to the guidelines recommended in the Guide for the Care and Use of Agricultural Animals in Agriculture Research and Teaching (Consortium, 1988). Procedures and animal care were approved by the University of Illinois Lab Animal Care Committee (Exp. 1 and Exp. 2) and the University of Nebraska Institute for Animal Care and Use Committee (Exp. 3).
Experiment 1
Animals.
This experiment was conducted at the University of Illinois Beef Research Unit in Urbana. The experiment lasted from January 5 through April 6, 2000 (92 d). One hundred seventy-five Angus-continental cross steers were assigned randomly to 25 pens on December 13, 1999, for a 20-d diet adjustment period, during which steers were adapted to final finishing diets by decreasing corn silage (nontransgenic) concentration from 35, to 25, to 15% (DM basis) and increasing corn at intervals of 6, 7, and 7 d, respectively. Steers were vaccinated upon arrival at the feedlot against Clostridium and Haemophlis somnus (Ultrabac 7/Somubac, Pfizer, Exton, PA), infectious bovine rhinotracheitis, bovine viral diarrhea, parainfluenza-3, bovine synctical respiratory virus (ViraShield 5, Grand Laboratories, Freeman, SD), and Pasturella haemolytica (One Shot, Pfizer, Exton, PA). Steers were implanted with Component TE-S with Tylan (TE-S, VetLife-Ivy Laboratories, Overland Park, KS) prior to the adaptation period. Steers were weighed individually on two consecutive days at the start and end of the experiment in the morning prior to feeding, and individual interim weights were taken at 28-d intervals. Final live weight was calculated by dividing hot carcass weight by the average dressing percentage, 61.90%. Steers were housed in pens with solid concrete floors (dimensions 4.3 m x 12.2 m) under an open front building facing south. All steers were placed in clean pens with 5 to 8 cm of wood shavings for bedding. Environmental conditions for the animals were consistent between treatments (i.e., floor space, temperature, lighting, animal density, feeder and water space). Animals were offered feed and water for ad libitum consumption. Feed was delivered once daily in the morning via a Data Ranger mixer (Model B113C; American Calan, Northwood, NH) with an onboard scale to deliver total mixed diets to individual pens. Scales were calibrated prior to initiation of the experiment.
Treatments.
Pens were assigned randomly to treatment with seven pens each being fed either the reference hybrids or the Roundup Ready corn. Due to limited quantities, only four pens were fed the near-isogenic control line. Four diets were formulated with different corn hybrids (Table 1). The four treatment diets consisted of 75% corn from one of either reference hybrid RX826 (REF1; Asgrow, Des Moines, IA), reference hybrid RX730 (REF2), near-isogenic control hybrid DK626 (CON; DEKALB Seeds, Dekalb, IA), or the test hybrid containing genetic modification for glyphosate tolerance (RR) event GA21 in hybrid line DK626. All corn hybrids were grown in Illinois, ground through a tub grinder (AGCO Farmhand, Duluth, GA; 1.9-cm screen), and stored in bottom unloading Harvestore silos as dry corn (<15% moisture). Particle-size analysis was conducted by the dry-sieving method, and no differences existed between corn hybrids following processing. Feed mixing equipment (Data Ranger; American Calan Inc., Northwood, NH) was flushed with corn silage between each batch to avoid cross-contamination. All diets were formulated to meet or exceed the NRC (1996) recommendations for finishing steers. Samples of totally mixed diets were sampled weekly and saved for nutrient analysis. The four corns were analyzed for CP, ash, ether extract (AOAC, 1999), and Ca, P, Mg, and K by inductively coupled plasma spectrometry to determine the nutrient profile of each hybrid (Dairy One, DHI Forage Analysis Laboratory, Ithaca, NY). The lowest nutrient concentrations of the four corns were used in formulating the supplement to meet dietary requirements. All diets contained monensin (29.8 mg/kg DM: Elanco Animal Health, Indianapolis, IN) and tylosin (11.1 mg/kg DM; Elanco Animal Health, Indianapolis, IN).
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). Longissimus muscle area was determined by use of images transposed onto chromatography paper and then traced and counted on a grid. Yield grade was calculated using fat depth, longissimus area, carcass weight, and KPH fat (Meat Evaluation Handbook, 2001). One steer was removed from the study due to a broken leg suffered during weighing. It was assumed that the steer consumed the same amount as the pen up to its removal on d 28.
Experiment 2
Animals.
One hundred ninety-six Angus-continental cross steers were allotted on December 13, 2000, for a diet adjustment period at the University of Illinois Beef Research Unit in Urbana. Steers were all implanted with Component TE-S (TE-S, Vetlife-Ivy Laboratories, Overland Park, KS) prior to the adjustment period. Steer allotment facilities, vaccinations, diet formulation, and management were the same as Exp. 1, with the exception that 28 pens of steers were allotted to the four corn treatments (seven pens/corn). No steers were removed prior to study completion.
Treatments.
Treatments were assigned randomly to each pen so that each treatment was represented once within a grouping of four pens to minimize potential variation due to pen location. All corn hybrids used for this experiment were grown on the University of Illinois farm. The treatments consisted of using either a Roundup Ready hybrid with event nk603 (RR), the near isogenic control hybrid RX670 (CON), reference hybrid DK647 (REF1; DEKALB Seeds, Dekalb, IA), or reference hybrid RX740 (REF2; Asgrow, Des Moines, IA) fed at 73% of diet DM (Table 1
). The four hybrids were analyzed at a commercial laboratory (Dairy One, DHI Forage Analysis Laboratory, Ithaca, NY), and supplements formulated as in Exp. 1. The experiment lasted from January 3 through April 7, 2001 (94 d).
Initial and final BW were based on the average of two weights taken on consecutive days. Similar to Exp. 1, ADG and feed efficiency (ADG/DMI) were calculated based on carcass adjusted final weights.
Carcasses.
Steers were marketed at a commercial abattoir (IBP, Joslin, IL). Hot carcass weights and the incidence of liver abscesses were collected following slaughter. Hot carcass weights were used to calculate final BW for each steer by dividing hot carcass weight by the average dressing percentage (61.1%). Average dressing percentages were calculated as carcass weight divided by final live weights collected on two consecutive days before slaughter. Remaining carcass measurements included 12th-rib fat thickness, KPH, and USDA-called marbling scores at the 12th rib, which were measured 24 h after harvest. Samples of longissimus muscle were collected approximately 24 h postharvest and analyzed similar to Exp. 1.
Experiment 3
Animals.
Two hundred crossbred steers were used in a completely randomized design to evaluate the effects of Roundup Ready (event nk603) corn on finishing performance and carcass composition. The steers were received at the University of Nebraska Agricultural Research and Development Center, Ithaca, NE, in the Fall of 2000 and grazed on corn residues while being supplemented with wet corn gluten feed until January 2001. After 5 d of limit feeding 50% alfalfa:50% wet corn gluten feed (DM basis) at 2% of BW, BW were recorded individually on two consecutive days in the morning prior to feeding for determination of initial BW (321 ± 13 kg). Individual weights were recorded every 28 d until market (144 d). Steers were implanted with Ralgro (Schering-Plough Animal Health, Union, NJ) at the beginning of the experiment and reimplanted on d 56 with Revalor-S (Intervet Inc., Somerville, NJ).
Treatments.
Steers were assigned to treatment by stratified weight recorded on d 0 and allocated to one of 20 pens (10 steers/pen) by random number. Pens were assigned randomly to one of four treatments. The treatment design was similar to Exp. 2, and the same four treatments were used. Five pens (replications) with 10 steers/pen were used for each treatment. All diets were formulated to meet or exceed NRC (1996) recommendations for digestible intake protein, undigestible intake protein, Ca, P, and K. Due to slight differences in nutrient analysis, the corn with the lowest content of CP (RR corn, 8.5% CP) was used as the input in the formulation model, so that any differences in performance would not be related to protein differences among treatments. Steers were adapted to final diets by replacing alfalfa hay with the treatment corn. Adaptation diets contained 45, 35, 25, and 15% roughage fed for 7 d each. The final diet after 28 d consisted of 79.5% dry-rolled corn and 7.5% ground alfalfa hay (DM basis; Table 1). All diets contained monensin (29.7 mg/kg DM; Elanco Animal Health, Indianapolis, IN) and tylosin (9.9 mg/kg DM; Elanco Animal Health, Indianapolis, IN) similar to current industry standards. The low moisture content of each of the corn hybrids (10.2 ± 1.0%) led to an increased amount of fines following processing (rolling). Therefore, steep liquor was included in the diet as a protein source to decrease fines and help to prevent sorting or diet separation.
This experiment was conducted as a blind study for feedlot personnel involved, similar to Exp. 1 and Exp. 2. Each hybrid was assigned a letter designation prior to initiation of the experiment, and all records, feed sheets, commodity bays, and pen assignments were acknowledged by letter designation throughout the experiment. Several measures were taken to prevent cross-contamination between hybrids throughout the study. Each hybrid of corn was rolled separately and stored in its own commodity bay that was sealed on all sides except the entrance. Nontransgenic corn, grown at the University of Nebraska’s Agricultural Research and Development Center, was utilized to clean out the mill and rolling system between hybrid processing. Based on DMI and transportation issues, grain was transported to the mill and processed at one time approximately once every 3 wk. At time of feeding, truck mixer boxes were cleaned out before and between each diet by feeding a diet that contained nontransgenic corn to nonstudy animals in the research unit. Steers were fed once daily in the morning using truck mixers (Rotomix, J-Star Industries, Inc., Dodge City, KS) with weighing capability. All scales for cattle and feeding were calibrated prior to study initiation.
Ingredient and bunk samples were taken weekly for all treatments. All ingredient and bunk samples were analyzed commercially (Dairy One, Ithaca, NY). Nutrient composition reported in Table 1 is based on ingredient analysis. As with Exp. 1 and Exp. 2, Monsanto (St. Louis, MO) evaluated presence or absence of the protein expressed by glyphosate tolerance genes using ELISA to confirm identity preservation.
Carcasses.
Steers were marketed based on visual appraisal of fat thickness (1.1 cm) and were marketed to a commercial abattoir (IBP, West Point, NE) on d 144. Hot carcass weights and liver abscess scores were taken on the day of slaughter. Fat thickness at the 12th rib, USDA-called yield grade, USDA-called marbling score, and longissimus muscle area were recorded following a 24-h chill. Additionally, one neck tissue (brachiocephalicus muscle) sample was collected from each carcass for proximate analysis. Five randomly selected muscle samples from each pen (5 of 10 carcasses) were analyzed for moisture, protein, and fat similar to Exp. 1 and Exp. 2 at the Experiment Station Chemical Laboratory, University of Missouri-Columbia. Calculations for final weight, ADG, and feed efficiency were based on hot carcass weights adjusted to a 63% common yield.
Statistical Analysis
Statistical analyses for feedlot growth performance and carcass characteristics were conducted using the MIXED procedure of SAS (SAS Inst., Inc., Cary, NC). Pen was the experimental unit for feedlot performance and carcass data in Exp. 1, Exp. 2, and Exp. 3. All experiments were analyzed as completely randomized designs. Two preplanned contrasts (RR vs. the average of REF1 and REF2; RR vs. CON) were utilized to compare the impact of glyphosate tolerance on performance and carcasses. An alpha level of 0.05 was assumed for significance to minimize type-I errors.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Steer ADG was not influenced (P > 0.05) by genetically enhanced corn hybrid in Exp. 1 (Table 2). Corn hybrid did cause significant variation in DMI based on the F-statistic (P = 0.05). However, no differences were detected in the preplanned contrasts between RR hybrid and CON or RR and the reference hybrids. Feed efficiency, measured as ADG/DMI, was not different (P > 0.05) among hybrids, suggesting no negative impacts on performance due to insertion of glyphosate tolerance genes. Averaged among treatments, efficiencies were 0.165 kg ADG/kg DMI. Carcasses from cattle fed RR contained more fat (P = 0.04) than the average of the cattle fed reference hybrids. Similarly, yield grade differences between RR and the reference hybrids approached significance (P = 0.08). Marbling scores for steers fed RR were higher than for steers fed CON corn and approached significance (P = 0.07). Despite greater fat depth, marbling scores were not different (P = 0.29) between RR and the average of the reference hybrids. However, the authors caution the reader that based on the F-statistic, little variation for fat depth and yield grade (P > 0.18) were attributable to corn hybrid. Marbling scores approached significance (P = 0.10) for the F-statistic. For almost all performance and carcass parameters measured, feeding RR resulted in performance intermediate to CON and the average of REF1 and REF2.
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Steers fed RR had similar ADG as steers fed either CON (P > 0.05) or conventional reference hybrids (P > 0.05) in Exp. 2 (Table 3). Similar to Exp. 1, significant variation was observed across the hybrids for DMI based on the F-statistic (P = 0.05). Based on the preplanned contrasts, the RR hybrid was not significantly different than either the CON or the average of the two reference hybrids. Averaged among treatments, steers gained 1.56 kg/d with feed efficiencies of 0.153 kg ADG/kg DMI. Carcass characteristics, including hot carcass weight, marbling, fat depth, and REA were unaffected by dietary treatment (P > 0.05) based on the F-statistic. Based on preplanned contrasts, carcasses from RR fed steers contained more fat (P = 0.09) than carcasses from steers fed the reference hybrids; however, the F-statistic was not significant suggesting little variation due to corn hybrid.
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No differences were observed among treatments for performance and carcass measurements recorded (Table 4). No differences occurred between RR and CON for final BW, DMI, ADG, hot carcass weight, marbling, or fat depth. The main effect of corn treatment was not significant for any variable. However, preplanned contrasts suggested that cattle fed CON had numerically greater efficiency (ADG/DMI) compared with animals on the RR treatment and approached significance (P = 0.08), although feed efficiency was not different between RR treatment and reference hybrids. The authors caution the reader as the F-statistic for feed efficiency was not significant (P = 0.22) suggesting little variation due to corn being fed.
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Meat composition is presented in Table 5. No differences were detected for moisture content of longissimus thoracis in either Exp. 1 or Exp. 2. Moisture content in Exp. 1 was 72.6% and 71.7% in Exp. 2. In Exp. 3, muscle composition was measured on a neck muscle (brachiocephalicus). Moisture content was not affected (P > 0.20) by corn hybrid fed and averaged 75.5% in Exp. 3. Protein, expressed on an as-is basis, was not affected by hybrid in Exp. 1, Exp. 2, or Exp. 3 and averaged 22.1, 23.9, or 20.1%, respectively. Similarly, fat content was not different among dietary treatments. Fat averaged 3.9, 4.3, and 3.7% for Exp. 1, Exp. 2, and Exp. 3, respectively. Interestingly, despite considerably greater fat depth in Exp. 3 compared with Exp. 1 or Exp. 2, fat content on an as-is basis was not higher for steers in Exp. 3. When corrected for moisture content, percentage fat in these muscle samples were 15.1% in Exp. 3 and 14.2 and 15.2% in Exp. 1 and Exp. 2, respectively.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Lack of differences among treatments observed in all three experiments agrees with previous research evaluating glyphosate-tolerant corn and soybeans fed to dairy cattle (Donkin et al., 2003; Hammond et al., 1996), pigs (Cromwell et al., 2001; Stanisiewski et al., 2001; Gaines et al., 2001a), and poultry (Gaines et al., 2001b; Taylor et al., 2003). Donkin et al. (2003) utilized silage and grain from Roundup Ready corn (event GA21) to examine effects of transgenic crops on feed intake, milk yield, and milk composition for sixteen lactating Holstein cows. The Roundup Ready treatment was contrasted against its control hybrid (DK626). Diets consisted of 62% corn silage and 17% corn grain from either the RR corn or the control corn. No differences in DMI, 21.5 vs. 21.9 ± 0.4; milk production, 29.4 vs. 29.5 ± 0.4; or milk composition were observed between RR and its control, respectively. The authors suggested those data demonstrated that lactating cows fed either the RR or the nontransgenic corn and silage perform similarly. Grant et al. (2003) also fed Roundup Ready corn silage and grain to lactating cows. In their study, differences observed were related to nutritional quality as a result of environmental conditions at silage harvest rather than transgenic traits. In contrast, Ipharraguerre et al. (2003) conducted a similar dairy cow study and did not detect any lactation performance differences using silages of comparable quality. Likewise, diets with RR corn had comparable feeding value to control and other commercially available hybrids fed to swine (Bressner et al., 2002; Fischer et al., 2002).
The differences observed in ADG and feed efficiency appear to be within normal ranges observed in the feedlot industry. While no data exist on these reference hybrids, some comparisons can be made to other research station reports with dry-rolled corn finishing diets. Owens et al. (1997) summarized grain source and processing data, including 183 trials with dry-rolled corn fed to finishing cattle. Gain, DMI, and feed conversion (DMI/ADG) averaged 1.45 kg/d, 9.45 kg/d, and 6.57, respectively. Considerable variation exists in feedlot performance; however, no standard errors were presented for these averages. In our experiments, feed:gain averaged 6.07, 6.53, and 6.02 for Exp. 1, Exp. 2, and Exp. 3, respectively. Therefore, we conclude that feeding Roundup Ready corn has no impact on livestock production compared with nontransgenic hybrids and results in average performance.
A power test was conducted on each experiment for ADG, DMI, and feed efficiency using PROC MIXED procedures of SAS (SAS Inst. Inc., Cary, NC). The observed mean square error from each performance parameter was used. The power test treatment structure was used where maximum power is evaluated. For these experiments with four treatments, this approach assumed two treatments were greater than the other two comparable treatments. Treatment differences were evaluated based on the observed range (which varied from 1.8 to 10.5% change), a 5% change in treatment means, and a 10% change in treatment means. For Exp. 1, the observed difference resulted in sufficient power (0.88) to avoid type-II errors for DMI as well as ADG (0.75; Table 6). In contrast, feed efficiency changes of 10% were necessary to detect differences with a power approaching 0.80 for Exp. 1. In both Exp. 2 and Exp. 3, a 10% change in treatment means was adequate for a power test of 0.80 except for feed efficiency in Exp. 2, which approached 0.70 power. The power test conducted here is dependent on variation, the difference between treatments, and number of replications. The power test supports that between a 5 to10% change in performance variables was adequately detected with the implemented experimental designs. The observed differences are not as meaningful as the percent change evaluated but are included for reference.
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Implications |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Inclusion of the glyphosate-tolerant gene(s) and the subsequent proteins that are produced in corn did not lead to practically important differences in animal growth performance or carcass composition. Feeding Roundup Ready corn to feedlot cattle had no effect on growth performance and seems equivalent to conventional, nontransgenic hybrids. Diets containing genetically enhanced corn should be balanced just as with conventional corn (i.e., based on nutrient analyses and ingredient quality).
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Footnotes |
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3 Current address: 1207 W. Gregory Dr. (phone: 217-333-2006; fax: 217-244-3169; E-mail: l-berger{at}uiuc.edu).
2 Correspondence: C220 Animal Science (phone: 402-472-6402; fax: 402-472-6362; E-mail: geericks{at}unlnotes.unl.edu).
Received for publication June 20, 2002. Accepted for publication May 16, 2003.
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Literature Cited |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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  A. L. Cerdeira and S. O. Duke The Current Status and Environmental Impacts of Glyphosate-Resistant Crops: A Review J. Environ. Qual., August 9, 2006; 35(5): 1633 - 1658. [Abstract] [Full Text] [PDF]
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 K. J. V. Pol, G. E. Erickson, N. D. Robbins, L. L. Berger, C. B. Wilson, T. J. Klopfenstein, E. P. Stanisiewski, and G. F. Hartnell Effects of grazing residues or feeding corn from a corn rootworm-protected hybrid (MON 863) compared with reference hybrids on animal performance and carcass characteristics J Anim Sci, December 1, 2005; 83(12): 2826 - 2834. [Abstract] [Full Text] [PDF]
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