Effect of feeding glyphosate-tolerant (roundup-ready events ga21 or nk603) corn compared with reference hybrids on feedlot steer performance and carcass characteristics

Effect of feeding glyphosate-tolerant (Roundup-Ready events GA21 or nk603)
corn compared with reference hybrids on feedlot steer performance
and carcass characteristics1
G. E. Erickson*2, N. D. Robbins†, J. J. Simon*, L. L. Berger†3 T. J. Klopfenstein*,
E. P. Stanisiewski‡, and G. F. Hartnell‡
*Department of Animal Science, University of Nebraska, Lincoln 68583-0908;†Department of Animal Science, University of Illinois, Urbana, IL 61801; and ABSTRACT:
tity-preserved protocols. In all experiments, DMI, ADG, compare the feeding value of genetically enhanced corn and feed efficiency were similar (P > 0.30) between RR (Roundup Ready corn events GA21 and nk603) with and REF. In Exp. 1 and Exp. 2, RR was not different nontransgenic hybrids. The four treatments included (P > 0.25) than CON for growth performance. In Exp.
two separate reference hybrids (REF), the near-isogenic 3, RR was not different from CON for ADG and DMI control hybrid (CON), and the genetically enhanced (P > 0.15) or for feed efficiency (P = 0.08). No differences corn (RR), resulting in two preplanned comparisons of were observed between RR and CON or RR and REF for CON vs. RR and RR vs. the average of REF. In Exp. 1 carcass weight, longissimus dorsi area, and marbling (RR event GA21), 175 steers (BW = 427 kg) were fed scores in any of the experiments. Subtle differences in 25 pens with seven pens per corn hybrid, except CON, were observed between RR and either CON or REF for which contained four pens due to limited quantities of fat depth in each experiment; however, cattle fed RR that hybrid. In Exp. 2 (RR event nk603), 196 steers were not consistently greater and varied from either (BW = 420 kg) were fed in 28 pens with seven pens per the CON or the REF (but not both contrasts) within an corn. In Exp. 3 (RR event nk603), 200 steers were fed experiment. Based on these results, insertion of glypho- in 20 pens, with a similar treatment design to Exp. 2 sate-tolerant genes had no significant effect on nutritive and five pens per corn. All experiments were conducted quality of corn. Performance and carcass characteristics as completely randomized designs and utilized corn pro- were not influenced, which suggests that Roundup duced at University of Illinois (Exp. 1 and 2) and Uni- Ready corn is similar to conventional, nontransgenic versity of Nebraska (Exp. 3) research farms under iden- corn when fed to finishing feedlot cattle.
Key Words: Animal Nutrition, Cattle, Finishing, Maize, Transgenic Plants 2003 American Society of Animal Science. All rights reserved. Introduction
Genetic engineering is one form of biotechnology thatis used to enhance the agronomic characteristics of Biotechnology has been adopted throughout many plants by inserting a gene or sequence of genes that facets of modern production agriculture. These innova- express desirable traits. Modern use of genetically engi- tions resulted in corn designed to be tolerant to glypho- neered crops has increased substantially. Between 1998 sate herbicides that have minimal soil leaching and low and 1999, the usage of genetically enhanced crops in- toxicity to mammals, birds, and fish (Sidhu et al., 2000).
creased 44% globally (27.8 vs. 39.9 million ha; Clarkand Ipharraguerre, 2001). Soybean acres planted thatwere genetically enhanced were 68% and 75% in 2001and 2002, respectively, while corn acres planted as ge- 1Published with the approval of the director as paper no. 13704, netically enhanced crops increased from 26% to 34% journal ser., Nebraska Agric. Res. Div.
for those years in the United States (USDA, 2002).
2Correspondence: C220 Animal Science (phone: 402-472-6402; fax: Glyphosate is a commercial herbicide that inhibits 402-472-6362; E-mail: geericks@unlnotes.unl.edu).
the enzyme 5-enolpyruvylshikimate-3-phosphate syn- 3Current address: 1207 W. Gregory Dr. (phone: 217-333-2006; fax: thase, which plays an important role in the shikimate 217-244-3169; E-mail: l-berger@uiuc.edu).
acid pathway that synthesizes essential aromatic amino acids required for plant growth (Steinru¨cken and Amrhein, 1980). Few data exist on the effect of feeding feed and water for ad libitum consumption. Feed was Roundup Ready corn to livestock. Because the majority delivered once daily in the morning via a Data Ranger of transgenic corn is fed to livestock, the nutritional mixer (Model B113C; American Calan, Northwood, NH) quality along with agronomic value must be assessed.
with an onboard scale to deliver total mixed diets to The hypothesis was that feedlot cattle fed Roundup individual pens. Scales were calibrated prior to initia- Ready corn will perform similar to cattle fed non- transgenic corn (i.e., the nutritional quality of corn is Treatments. Pens were assigned randomly to treat- not changed as a result of Roundup Ready technology).
ment with seven pens each being fed either the refer- The objective of this research was to compare growth ence hybrids or the Roundup Ready corn. Due to limited performance and carcass characteristics of finishing quantities, only four pens were fed the near-isogenic steers fed Roundup Ready corn (event GA21 and nk603) control line. Four diets were formulated with different to their near-isogenic control hybrid and two reference corn hybrids (Table 1). The four treatment diets con- sisted of 75% corn from one of either reference hybrid
RX826 (REF1; Asgrow, Des Moines, IA), reference hy-
Materials and Methods
brid RX730 (REF2), near-isogenic control hybrid
DK626 (CON; DEKALB Seeds, Dekalb, IA), or the test
Steers used in these experiments were managed ac- hybrid containing genetic modification for glyphosate cording to the guidelines recommended in the Guide for tolerance (RR) event GA21 in hybrid line DK626. All
the Care and Use of Agricultural Animals in Agriculture corn hybrids were grown in Illinois, ground through Research and Teaching (Consortium, 1988). Procedures a tub grinder (AGCO Farmhand, Duluth, GA; 1.9-cm and animal care were approved by the University of screen), and stored in bottom unloading Harvestore si- Illinois Lab Animal Care Committee (Exp. 1 and Exp.
los as dry corn (<15% moisture). Particle-size analysis 2) and the University of Nebraska Institute for Animal was conducted by the dry-sieving method, and no differ- ences existed between corn hybrids following pro-cessing. Feed mixing equipment (Data Ranger; Ameri- can Calan Inc., Northwood, NH) was flushed with cornsilage between each batch to avoid cross-contamination.
Animals. This experiment was conducted at the Uni- All diets were formulated to meet or exceed the NRC versity of Illinois Beef Research Unit in Urbana. The (1996) recommendations for finishing steers. Samples experiment lasted from January 5 through April 6, 2000 of totally mixed diets were sampled weekly and saved (92 d). One hundred seventy-five Angus-continental for nutrient analysis. The four corns were analyzed for cross steers were assigned randomly to 25 pens on De- CP, ash, ether extract (AOAC, 1999), and Ca, P, Mg, cember 13, 1999, for a 20-d diet adjustment period, and K by inductively coupled plasma spectrometry to during which steers were adapted to final finishing diets determine the nutrient profile of each hybrid (Dairy by decreasing corn silage (nontransgenic) concentration One, DHI Forage Analysis Laboratory, Ithaca, NY). The from 35, to 25, to 15% (DM basis) and increasing corn lowest nutrient concentrations of the four corns were at intervals of 6, 7, and 7 d, respectively. Steers were used in formulating the supplement to meet dietary vaccinated upon arrival at the feedlot against Clostrid- requirements. All diets contained monensin (29.8 mg/ ium and Haemophlis somnus (Ultrabac 7/Somubac, kg DM: Elanco Animal Health, Indianapolis, IN) and Pfizer, Exton, PA), infectious bovine rhinotracheitis, tylosin (11.1 mg/kg DM; Elanco Animal Health, India- bovine viral diarrhea, parainfluenza-3, bovine synctical respiratory virus (ViraShield 5, Grand Laboratories, Carcasses. One hundred sixty steers were marketed Freeman, SD), and Pasturella haemolytica (One Shot, at a commercial abattoir (IBP, Joslin, IL) when visually Pfizer, Exton, PA). Steers were implanted with Compo- appraised to have 1.0 cm of subcutaneous fat. Individ- nent TE-S with Tylan (TE-S, VetLife-Ivy Laboratories, ual carcass measurements were taken for carcass Overland Park, KS) prior to the adaptation period.
weight, incidence of liver abscesses, 12th-rib fat, kid- Steers were weighed individually on two consecutive ney, pelvic, and heart (KPH) fat, USDA-called marbling
days at the start and end of the experiment in the score, and longissimus dorsi area (REA). Dressing per-
morning prior to feeding, and individual interim centage and yield grade were calculated using these weights were taken at 28-d intervals. Final live weight data. Fourteen steers (one pen from RR, and one CON) was calculated by dividing hot carcass weight by the were slaughtered separately at the University of Illinois average dressing percentage, 61.90%. Steers were Meats abattoir to conduct more complete sampling of housed in pens with solid concrete floors (dimensions the carcass for gene testing (data not shown). Similar 4.3 m × 12.2 m) under an open front building facing carcass measurements were collected on those steers south. All steers were placed in clean pens with 5 to 8 and included in the analysis. A trained University of cm of wood shavings for bedding. Environmental condi- Illinois employee assigned marbling scores to all car- tions for the animals were consistent between treat- casses. Marbling scores for both groups were assigned ments (i.e., floor space, temperature, lighting, animal as follows: 400 = slight, 500 = small, 600 = modest, 700 density, feeder and water space). Animals were offered = moderate, 800 = slightly abundant, 900 = moderately Table 1. Finishing diet composition fed to finishing steers in Exp. 1, Exp. 2, and Exp. 3.
Corn grain was the variable changed in each treatment dieta aPercentage of dietary DM.
bREF1 = Reference (Asgrow RX826), REF2 = Reference (Asgrow 730), CON = Near isogenic control (DK626), RR = Roundup Ready (DK626RR; event GA21) corn.
cREF1 = Reference DEKALB hybrid DK647, REF2 = Reference Asgrow hybrid RX740, CON = Near isogenic control hybrid RX670, and RR = Roundup Ready hybrid (event nk603).
dSupplement fed in meal form and formulated to be fed at 10% (Exp. 1 and Exp. 2) or 3% of diet DM (Exp. 3) and were identical across treatments within each experiment.
eTrace mineral salt with Se, composition is salt: 81 to 86%, Fe: 2.57%, Zn: 2.86%, Mn: 5,710 mg/kg, Cu: 2,290 mg/kg, I: 100 mg/kg, Se: 85.7 mg/kg.
fPremix contained 12% Zn, 10% Fe, 8% Mn, 1.5% Cu, 0.2% I, 0.10% Co.
gPremix contained 176 g/kg Monensin.
hPremix contained 88 g/kg Tylosin.
iPremix contained 3,300 IU vitamin A, 330 IU vitamin D, 44 IU vitamin E per gram (Exp. 1 and Exp. 2) and 1,500 IU vitamin A, 3,000 IU vitamin D, 3.7 IU vitamin E per gram (Exp. 3).
jBased on composited ingredient samples (Analysis by Dairy One, Ithaca, NY).
abundant, 1,000 = abundant. A cross section (0.8-cm with Component TE-S (TE-S, Vetlife-Ivy Laboratories, thick) of longissimus thoracis muscle was collected from Overland Park, KS) prior to the adjustment period.
each carcass and analyzed for fat by acid hydrolysis, Steer allotment facilities, vaccinations, diet formula- protein by Kjeldahl N, and water content (AOAC, 1999).
tion, and management were the same as Exp. 1, with Longissimus muscle area was determined by use of the exception that 28 pens of steers were allotted to the images transposed onto chromatography paper and four corn treatments (seven pens/corn). No steers were then traced and counted on a grid. Yield grade was calculated using fat depth, longissimus area, carcass Treatments. Treatments were assigned randomly to weight, and KPH fat (Meat Evaluation Handbook, each pen so that each treatment was represented once within a grouping of four pens to minimize potential One steer was removed from the study due to a broken variation due to pen location. All corn hybrids used for leg suffered during weighing. It was assumed that the this experiment were grown on the University of Illinois steer consumed the same amount as the pen up to its farm. The treatments consisted of using either a Roundup Ready hybrid with event nk603 (RR), the nearisogenic control hybrid RX670 (CON), reference hybrid DK647 (REF1; DEKALB Seeds, Dekalb, IA), or refer- Animals. One hundred ninety-six Angus-continental ence hybrid RX740 (REF2; Asgrow, Des Moines, IA) fed cross steers were allotted on December 13, 2000, for a at 73% of diet DM (Table 1). The four hybrids were diet adjustment period at the University of Illinois Beef analyzed at a commercial laboratory (Dairy One, DHI Research Unit in Urbana. Steers were all implanted Forage Analysis Laboratory, Ithaca, NY), and supple- ments formulated as in Exp. 1. The experiment lasted (DM basis; Table 1). All diets contained monensin (29.7 from January 3 through April 7, 2001 (94 d).
mg/kg DM; Elanco Animal Health, Indianapolis, IN) Initial and final BW were based on the average of and tylosin (9.9 mg/kg DM; Elanco Animal Health, Indi- two weights taken on consecutive days. Similar to Exp.
anapolis, IN) similar to current industry standards. The 1, ADG and feed efficiency (ADG/DMI) were calculated low moisture content of each of the corn hybrids (10.2 based on carcass adjusted final weights.
± 1.0%) led to an increased amount of fines following Carcasses. Steers were marketed at a commercial ab- processing (rolling). Therefore, steep liquor was in- attoir (IBP, Joslin, IL). Hot carcass weights and the cluded in the diet as a protein source to decrease fines incidence of liver abscesses were collected following and help to prevent sorting or diet separation.
slaughter. Hot carcass weights were used to calculate This experiment was conducted as a blind study for final BW for each steer by dividing hot carcass weight feedlot personnel involved, similar to Exp. 1 and Exp.
by the average dressing percentage (61.1%). Average 2. Each hybrid was assigned a letter designation prior dressing percentages were calculated as carcass weight to initiation of the experiment, and all records, feed divided by final live weights collected on two consecu- sheets, commodity bays, and pen assignments were ac- tive days before slaughter. Remaining carcass measure- knowledged by letter designation throughout the exper- ments included 12th-rib fat thickness, KPH, and iment. Several measures were taken to prevent cross- USDA-called marbling scores at the 12th rib, which contamination between hybrids throughout the study.
were measured 24 h after harvest. Samples of longissi- Each hybrid of corn was rolled separately and stored mus muscle were collected approximately 24 h posthar- in its own commodity bay that was sealed on all sides vest and analyzed similar to Exp. 1.
except the entrance. Nontransgenic corn, grown at the University of Nebraska’s Agricultural Research andDevelopment Center, was utilized to clean out the mill Animals. Two hundred crossbred steers were used in and rolling system between hybrid processing. Based a completely randomized design to evaluate the effects on DMI and transportation issues, grain was trans- of Roundup Ready (event nk603) corn on finishing per- ported to the mill and processed at one time approxi- formance and carcass composition. The steers were re- mately once every 3 wk. At time of feeding, truck mixer ceived at the University of Nebraska Agricultural Re- boxes were cleaned out before and between each diet search and Development Center, Ithaca, NE, in the by feeding a diet that contained nontransgenic corn to Fall of 2000 and grazed on corn residues while being nonstudy animals in the research unit. Steers were fed supplemented with wet corn gluten feed until January once daily in the morning using truck mixers (Rotomix, 2001. After 5 d of limit feeding 50% alfalfa:50% wet J-Star Industries, Inc., Dodge City, KS) with weighing corn gluten feed (DM basis) at 2% of BW, BW were capability. All scales for cattle and feeding were cali- recorded individually on two consecutive days in the morning prior to feeding for determination of initial Ingredient and bunk samples were taken weekly for BW (321 ± 13 kg). Individual weights were recorded all treatments. All ingredient and bunk samples were every 28 d until market (144 d). Steers were implanted analyzed commercially (Dairy One, Ithaca, NY). Nutri- with Ralgro (Schering-Plough Animal Health, Union, ent composition reported in Table 1 is based on ingredi- NJ) at the beginning of the experiment and reimplanted ent analysis. As with Exp. 1 and Exp. 2, Monsanto (St.
on d 56 with Revalor-S (Intervet Inc., Somerville, NJ).
Louis, MO) evaluated presence or absence of the protein Treatments. Steers were assigned to treatment by expressed by glyphosate tolerance genes using ELISA stratified weight recorded on d 0 and allocated to one of 20 pens (10 steers/pen) by random number. Pens Carcasses. Steers were marketed based on visual ap- were assigned randomly to one of four treatments. The praisal of fat thickness (1.1 cm) and were marketed to treatment design was similar to Exp. 2, and the same a commercial abattoir (IBP, West Point, NE) on d 144.
four treatments were used. Five pens (replications) Hot carcass weights and liver abscess scores were taken with 10 steers/pen were used for each treatment. Alldiets were formulated to meet or exceed NRC (1996) on the day of slaughter. Fat thickness at the 12th rib, recommendations for digestible intake protein, undi- USDA-called yield grade, USDA-called marbling score, gestible intake protein, Ca, P, and K. Due to slight and longissimus muscle area were recorded following differences in nutrient analysis, the corn with the low- a 24-h chill. Additionally, one neck tissue (brachioceph- est content of CP (RR corn, 8.5% CP) was used as the alicus muscle) sample was collected from each carcass input in the formulation model, so that any differences for proximate analysis. Five randomly selected muscle in performance would not be related to protein differ- samples from each pen (5 of 10 carcasses) were analyzed ences among treatments. Steers were adapted to final for moisture, protein, and fat similar to Exp. 1 and diets by replacing alfalfa hay with the treatment corn.
Exp. 2 at the Experiment Station Chemical Laboratory, Adaptation diets contained 45, 35, 25, and 15% rough- University of Missouri-Columbia. Calculations for final age fed for 7 d each. The final diet after 28 d consisted weight, ADG, and feed efficiency were based on hot of 79.5% dry-rolled corn and 7.5% ground alfalfa hay carcass weights adjusted to a 63% common yield.
Table 2. Performance and carcass characteristics in Exp. 1 for steers fed either commercial reference hybrids,
near-isogenic control hybrid, or Roundup Ready corn (event GA21) for 92 d aREF1 = Reference (Asgrow RX826), REF2 = Reference (Asgrow 730), CON = Near isogenic control (DK626), RR = Roundup Ready (DK626RR; bBased on hot carcass weight adjusted by a common dress (61.9%).
cObservations were carcass weight (n = 174), Marbling score (n = 171), REA, fat depth, and yield grade (n = 157).
dMarbling score in which Slight 50 = 450, Small 50 = 550.
eREA is longissimus muscle area measured between the 12th and 13th ribs.
fYield grade was calculated using fat depth, longissimus muscle area, carcass weight, and kidney, pelvic, and heart fat (Meat Evaluation and approached significance (P = 0.07). Despite greaterfat depth, marbling scores were not different (P = 0.29) Statistical analyses for feedlot growth performance between RR and the average of the reference hybrids.
and carcass characteristics were conducted using the However, the authors caution the reader that based on MIXED procedure of SAS (SAS Inst., Inc., Cary, NC).
the F-statistic, little variation for fat depth and yield Pen was the experimental unit for feedlot performance grade (P > 0.18) were attributable to corn hybrid. Mar- and carcass data in Exp. 1, Exp. 2, and Exp. 3. All bling scores approached significance (P = 0.10) for the experiments were analyzed as completely randomized F-statistic. For almost all performance and carcass pa- designs. Two preplanned contrasts (RR vs. the average rameters measured, feeding RR resulted in perfor- of REF1 and REF2; RR vs. CON) were utilized to com- mance intermediate to CON and the average of REF1 pare the impact of glyphosate tolerance on performance and carcasses. An alpha level of 0.05 was assumed forsignificance to minimize type-I errors.
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 DMIbased on the F-statistic (P = 0.05). Based on the pre- Steer ADG was not influenced (P > 0.05) by geneti- planned contrasts, the RR hybrid was not significantly cally enhanced corn hybrid in Exp. 1 (Table 2). Corn different than either the CON or the average of the two hybrid did cause significant variation in DMI based on reference hybrids. Averaged among treatments, steers the F-statistic (P = 0.05). However, no differences were gained 1.56 kg/d with feed efficiencies of 0.153 kg ADG/ detected in the preplanned contrasts between RR hy- kg DMI. Carcass characteristics, including hot carcass brid and CON or RR and the reference hybrids. Feed weight, marbling, fat depth, and REA were unaffected efficiency, measured as ADG/DMI, was not different (P by dietary treatment (P > 0.05) based on the F-statistic.
> 0.05) among hybrids, suggesting no negative impacts Based on preplanned contrasts, carcasses from RR fed on performance due to insertion of glyphosate tolerance steers contained more fat (P = 0.09) than carcasses from genes. Averaged among treatments, efficiencies were steers fed the reference hybrids; however, the F-statis- 0.165 kg ADG/kg DMI. Carcasses from cattle fed RR tic was not significant suggesting little variation due contained more fat (P = 0.04) than the average of the cattle fed reference hybrids. Similarly, yield grade dif- ferences between RR and the reference hybrids ap-proached significance (P = 0.08). Marbling scores for No differences were observed among treatments for steers fed RR were higher than for steers fed CON corn performance and carcass measurements recorded (Ta- Table 3. Performance and carcass characteristics in Exp. 2 for steers fed either commercial reference hybrids,
near-isogenic control hybrid, or Roundup Ready corn (event nk603) for 94 d aREF1 = Reference hybrid DK647, REF2 = Reference hybrid RX740, CON = Near isogenic control hybrid RX670, and RR = Roundup Ready bBased on hot carcass weight adjusted by common dress (61.1%).
cObservations were carcass weight (n = 174), Marbling score (n = 171), REA, fat depth, and yield grade (n = 157).
dMarbling score in which Slight 50 = 450, Small 50 = 550.
eREA is longissimus muscle area measured between the 12th and 13th ribs.
fYield grade was calculated using fat depth, longissimus muscle area, carcass weight, and kidney, pelvic, and heart fat (Meat Evaluation ble 4). No differences occurred between RR and CON No differences in BW, DMI, ADG, or feed efficiency for final BW, DMI, ADG, hot carcass weight, marbling, were observed between the average of REF1 and REF2 or fat depth. The main effect of corn treatment was compared with steers fed RR. Feeding conventional ref- not significant for any variable. However, preplanned erence hybrids resulted in slightly more (P = 0.05) 12th- contrasts suggested that cattle fed CON had numeri- rib fat depth compared with the RR treatment. How- cally greater efficiency (ADG/DMI) compared with ani- ever, all steers were quite fat (1.6-cm fat depth). Fat mals on the RR treatment and approached significance depth was considerably greater in Exp. 3 than in Exp.
(P = 0.08), although feed efficiency was not different 1 or Exp. 2. No other differences in carcass traits (hot between RR treatment and reference hybrids. The au- carcass weight, marbling, or REA) were observed be- thors caution the reader as the F-statistic for feed effi- ciency was not significant (P = 0.22) suggesting little Meat composition is presented in Table 5. No differ- ences were detected for moisture content of longissimus Table 4. Performance and carcass characteristics in Exp. 3 for steers fed either commercial reference hybrids,
near-isogenic control hybrid, or Roundup Ready corn (event nk603) for 144 d aREF1 = Reference hybrid DK647, REF2 = Reference hybrid RX740, CON = Near isogenic control hybrid RX670, and RR = Roundup Ready bBased on hot carcass weight adjusted to a common dress (63%).
cMarbling score in which Small 0 = 500, Small 50 = 550.
d REA is longissimus muscle area measured between the 12th and 13th ribs.
Table 5. Muscle composition of selected muscles from Exp. 1, Exp. 2, and Exp. 3a
aPercent as-is, expressed as g/100 g.
bREF1 = Reference (Asgrow RX826), REF2 = Reference (Asgrow 730), CON = Near isogenic control (DK626), RR = Roundup Ready (DK626RR; event GA21) corn.
cREF1 = Reference hybrid DK647, REF2 = Reference hybrid RX740, CON = Near isogenic control hybrid RX670, and RR = Roundup Ready hybrid (event nk603).
thoracis in either Exp. 1 or Exp. 2. Moisture content in Ready corn silage and grain to lactating cows. In their Exp. 1 was 72.6% and 71.7% in Exp. 2. In Exp. 3, muscle study, differences observed were related to nutritional composition was measured on a neck muscle (brachio- quality as a result of environmental conditions at silage cephalicus). Moisture content was not affected (P > 0.20) harvest rather than transgenic traits. In contrast, Ipha- by corn hybrid fed and averaged 75.5% in Exp. 3. Pro- rraguerre et al. (2003) conducted a similar dairy cow tein, expressed on an as-is basis, was not affected by study and did not detect any lactation performance dif- hybrid in Exp. 1, Exp. 2, or Exp. 3 and averaged 22.1, ferences using silages of comparable quality. Likewise, 23.9, or 20.1%, respectively. Similarly, fat content was diets with RR corn had comparable feeding value to not different among dietary treatments. Fat averaged control and other commercially available hybrids fed 3.9, 4.3, and 3.7% for Exp. 1, Exp. 2, and Exp. 3, respec- to swine (Bressner et al., 2002; Fischer et al., 2002).
tively. Interestingly, despite considerably greater fat The differences observed in ADG and feed efficiency depth in Exp. 3 compared with Exp. 1 or Exp. 2, fat appear to be within normal ranges observed in the feed- content on an as-is basis was not higher for steers in lot industry. While no data exist on these reference Exp. 3. When corrected for moisture content, percent- hybrids, some comparisons can be made to other re- age fat in these muscle samples were 15.1% in Exp. 3 search station reports with dry-rolled corn finishing and 14.2 and 15.2% in Exp. 1 and Exp. 2, respectively.
diets. Owens et al. (1997) summarized grain source andprocessing data, including 183 trials with dry-rolled Discussion
corn fed to finishing cattle. Gain, DMI, and feed conver-sion (DMI/ADG) averaged 1.45 kg/d, 9.45 kg/d, and 6.57, Lack of differences among treatments observed in respectively. Considerable variation exists in feedlot all three experiments agrees with previous research performance; however, no standard errors were pre- evaluating glyphosate-tolerant corn and soybeans fed sented for these averages. In our experiments, feed:gain to dairy cattle (Donkin et al., 2003; Hammond et al., averaged 6.07, 6.53, and 6.02 for Exp. 1, Exp. 2, and 1996), pigs (Cromwell et al., 2001; Stanisiewski et al., Exp. 3, respectively. Therefore, we conclude that feed- 2001; Gaines et al., 2001a), and poultry (Gaines et al., ing Roundup Ready corn has no impact on livestock 2001b; Taylor et al., 2003). Donkin et al. (2003) utilized production compared with nontransgenic hybrids and silage and grain from Roundup Ready corn (event GA21) to examine effects of transgenic crops on feed A power test was conducted on each experiment for intake, milk yield, and milk composition for sixteen ADG, DMI, and feed efficiency using PROC MIXED lactating Holstein cows. The Roundup Ready treatment procedures of SAS (SAS Inst. Inc., Cary, NC). The ob- was contrasted against its control hybrid (DK626).
served mean square error from each performance pa- Diets consisted of 62% corn silage and 17% corn grain rameter was used. The power test treatment structure from either the RR corn or the control corn. No differ- was used where maximum power is evaluated. For ences in DMI, 21.5 vs. 21.9 ± 0.4; milk production, 29.4 these experiments with four treatments, this approach vs. 29.5 ± 0.4; or milk composition were observed be- assumed two treatments were greater than the other tween RR and its control, respectively. The authors two comparable treatments. Treatment differences suggested those data demonstrated that lactating cows were evaluated based on the observed range (which fed either the RR or the nontransgenic corn and silage varied from 1.8 to 10.5% change), a 5% change in treat- perform similarly. Grant et al. (2003) also fed Roundup ment means, and a 10% change in treatment means.
Table 6. Power analysis results for Exp. 1, Exp. 2, and Exp. 3 performance
measurements to determine likelihood of a type-II error. Three treatment differences were evaluated for power using actual observed differences in means, a 5% change in means, and a 10% change in means aPercent change calculated as observed difference divided by average of all treatment means.
For Exp. 1, the observed difference resulted in sufficient cally enhanced corn should be balanced just as with power (0.88) to avoid type-II errors for DMI as well as conventional corn (i.e., based on nutrient analyses and ADG (0.75; Table 6). In contrast, feed efficiency changes of 10% were necessary to detect differences with a powerapproaching 0.80 for Exp. 1. In both Exp. 2 and Exp.
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