J. Anim. Sci. 2005. 83:400-407
© 2005 American Society of Animal Science
Nutrient digestibility in sheep fed diets containing Roundup Ready or conventional fodder beet, sugar beet, and beet pulp1
G. F. Hartnell*,2,
T. Hvelplund
and
M. R. Weisbjerg
* Monsanto Co., St. Louis, MO 63167; and
and
Danish Institute of Agricultural Sciences, Department of Animal Nutrition and Physiology, Research Centre Foulum, Tjele, Denmark
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Abstract
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The objective of this digestibility assessment was to determine whether there are significant differences in the digestibility of Roundup Ready (glyphosate-tolerant) and conventional sugar beet, fodder beet, and beet pulp produced from sugar beet varieties when fed to sheep (seven wethers per treatment group). Three experiments were conducted in this assessment. Experiment 1 (35 wethers) compared one glyphosate-tolerant fodder beet variety with four conventional varieties, Exp. 2 (42 wethers) compared one glyphosate-tolerant sugar beet variety with five conventional varieties, and Exp. 3 (42 wethers) compared beet pulp derived from glyphosate-tolerant sugar beet with beet pulp from five European locations. The experimental phase consisted of a 2-wk preliminary period followed by a 1-wk collection period for Exp. 1 and 2, and a 1-wk preliminary period followed by a 1-wk digestibility collection period for Exp. 3. Diets were comprised of grass hay at 30, 30, and 20% of DM for Exp. 1, 2, and 3, respectively, with the balance being beet components. Urea and sodium sulfate were supplemented (8 and 2.9 g, respectively, for Exp. 1 and 2; and 6 g and 2.16 g, respectively, for Exp. 3) to supply sufficient dietary N and S. Each diet was fed to sheep (96 ± 0.9 kg) in the three experiments to at or near maintenance energy levels. Treatment differences were considered significant at P < 0.05. Apparent digestibilities of DM, OM, CP, NDF, ADF, and DE for glyphosate-tolerant fodder and sugar beets did not differ from those for commercial fodder and sugar beets in Exp. 1 and 2. There were differences (P < 0.05) in DM, OM, CP, NDF, ADF, and DE digestibilities influenced by the different varieties of beet pulp in Exp. 3, but these were not unique to just the Roundup Ready sugar beet variety. Digestibilities and feeding values of Roundup Ready fodder beet, sugar beet, and beet pulp produced from Roundup Ready sugar beet varieties were not influenced by the introduction of the Roundup Ready trait compared with conventional varieties.
Key Words: Beet • Digestibility • Pulp • Sheep • Transgenic
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Introduction
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Fodder and sugar beet varieties tolerant to glyphosate, the active ingredient in the Roundup family of agricultural herbicides, have been developed through genetic engineering to improve weed management and crop productivity. The glyphosate tolerance is due to the production of a specific protein, CP4 5-enolpyruvyl-shikimate-3-phosphate synthase (Padgette et al., 1996
). The enzyme, 5-enolpyruvylshikimate-3-phosphate synthase, catalyzes the formation of EPSP from shikimate-3-phosphate and phosphoenolpyruvate in both microorganisms and plants. Its activity is inhibited by glyphosate. The expressed protein, CP4 5-enolpyruvylshiki-mate-3-phosphate synthase, is a naturally occurring glyphosate-tolerant 5-enolpyruvylshikimate-3-phosphate synthase that has been isolated from Agrobacterium sp. strain CP4 and, when produced in crop plants, confers tolerance to glyphosate, the active ingredient in the Roundup family of agricultural herbicides (Padgette et al., 1996). Previous research has demonstrated nutritional equivalence in poultry and livestock when fed Roundup Ready soybeans (Hammond et al., 1996; Cromwell et al., 2002), Roundup Ready corn (Taylor et al., 2003; Hyun et al., 2004; Ipharraguerre et al., 2003), or Roundup Ready canola (Stanford et al., 2003).
The primary market for fodder beets (beet varieties developed and grown especially for feed) and beet pulp derived from sugar beets (beet varieties developed and grown for high sugar content) is ruminants. Therefore, the objective of the present studies was to determine whether Roundup Ready fodder beet, Roundup Ready sugar beet, and beet pulp derived from Roundup Ready sugar beet varieties differ in apparent total-tract digestibility and feeding value from commercial nongenetically modified (conventional) varieties when fed to sheep.
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Materials and Methods
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Beet Sources
Experiment 1 used five different fodder beet varieties, including glyphosate-tolerant fodder beet containing transformation event A5/15 and four conventional fodder beet varieties. Experiment 2 was conducted with Roundup Ready sugar beet containing transformation event H7-1 and five conventional sugar beet varieties. Experiment 3 was conducted with beet pulp derived from Roundup Ready sugar beet containing transformation event 77 and beet pulp from five conventional varieties. All sugar beet and fodder beet varieties were delivered in bags for the digestibility experiments.
Beet Processing
Fodder beet (Exp. 1) and sugar beet (Exp. 2) materials were prepared for the digestibility experiment in the following manner. Beet roots were dumped and mixed in a feeder wagon and then taken through a processing line consisting of a shaker belt, a dry cleaner, a washing machine, and finally a cutter (system fabricated by Danish Institute of Agricultural Sciences; Foulum, Denmark). Dry matter content of the different varieties was measured after washing and cutting. After cutting the beetroots (approximately 1 cm in height and width and 3 cm in length), they were packaged in labeled plastic bags containing approximately 700 (Exp. 1) and 650 g of DM (Exp. 2) per bag. After weighing, the plastic bags containing the cut beetroots were stored in a freezer at approximately –18°C until further use. Sugar beets (Exp. 3) were processed and the beet pulp was pressed and dried in a pilot plant at Danisco Development Center (Nakskov, Denmark). The dried pulp was delivered to Research Center Foulum in labeled bags containing approximately 750 g of DM per bag The packaged beet pulp was stored at room temperature. During packaging of the different varieties, representative samples were taken for chemical analysis. Frozen bags were allowed to thaw at room temperature for 24 h before feeding.
For Exp. 1, five varieties of fodder beet (conventional varieties Nestor, Magnum, Kyros, and Troya and Roundup Ready fodder beet A5/15) were delivered in bags from DLF-Trifolium (Roskilde, Denmark). Six varieties of sugar beet (conventional varieties Roberta, Madison, Atlantis, Corina, and Access and Roundup Ready sugar beet H7-1) were delivered in bags from KWS (Einbeck, Germany) for Exp. 2. Six beet pulp samples derived from sugar beet (conventional varieties obtained from Nakskov, Denmark; Norwich, England; Gørlev, Denmark; Palencia, Spain; and Warcoing, Belgium) and Roundup Ready sugar beet 77 pulp from Nakskov, Denmark were delivered from Danisco Seed (Copenhagen, Denmark) for Exp. 3. For all experiments, bags were stored at room temperature in the feed storage room in the experimental unit after delivery. At delivery, five bags from each variety were randomly selected for further analysis, including nutrient composition.
Animals and Experimental Design
For Exp. 1, 2, and 3, 35, 42, and 42 wethers of Leicester breed (2 to 7 yr of age) weighing 98 ± 4.1, 95 ± 4.4, and 94 ± 2.3 kg, respectively, were used. Body weights were recorded for each animal after the morning feeding at the beginning and end of each experiment. Health of animals was inspected by the attending veterinarian both at the beginning and end of each experiment. Sheep were observed daily for signs of illness. Animals were allocated to each metabolism crate (1.5 m long x 0.6 m wide) and remained on study for 14 d (except 7 d for Exp. 3) for the adaptation period and 7 d for the excreta collection. Water was freely accessible throughout experiments via individual water cups, which were checked daily and cleaned as needed to ensure a clean water supply to animals at all times during the experiments.
Experiments were conducted as a randomized block design, with location in the digestibility unit as the block, such that animals were assigned randomly to one of five treatments for Exp. 1 and one of six treatments for Exp. 2 and 3 within each block. The location of the crates in the facility was used as a block because there was no previously established work in this facility showing no effect of environment, such as ventilation and people traffic on the performance of animals. Daily rations contained 717 ± 9 g DM of fodder beet and 299 g DM of grass hay for Exp. 1; 617 ± 32 g DM of sugar beet and 300 ± 1 g DM of hay for Exp. 2; and 750 g DM of beet pulp and 201 g DM of grass hay for Exp. 3, and were near maintenance levels. To obtain sufficient CP to meet the dietary requirement (NRC, 1985) for N and S for the ruminal microbes, 8 g of urea and 2.9 g of sodium sulfate for Exp. 1 and 2, and 6 g of urea and 2.16 g of sodium sulfate for Exp. 3 were added to maintain a N:S ratio of 13:1. Urea and sodium sulfate were dissolved in 50 mL water and added to the daily feed ration (25 mL per feeding) on top of the meal after hay was fed on the bottom and beet treatments were fed on top of the hay in the manger. The daily ration was fed to the sheep in two meals at 0700 to 0730 and 1400 to 1430 for Exp. 1, and 0800 to 0830 and 1500 to 1530 for Exp. 2 and 3. Sheep were kept individually in crates (1.5 m x 0.6 m) that were housed in a single room in a barn that was well ventilated. The temperature in the barn was not measured during experiments, but ventilators were adjusted to activate at a temperature of 10 °C.
Collections and Analyses
Beet samples were collected throughout the cutting process, 15 subsamples were composited, sampled, and analyzed. Hay samples for the lot were taken and analyzed. Feces were collected into plastic bags mounted on each sheep by a harness for 7 d after the adaptation period. Bags were emptied once daily after the morning feeding. Feces for each individual sheep were pooled and frozen until the end of each experiment, when frozen feces were mixed and chopped before freeze-drying and subsequent analysis. Feed ingredients and dried feces were ground to pass a 1-mm screen in a hammer mill before analysis. Beet products, hay, and feces were analyzed for moisture and CP according to AOAC (1990); NDF and ADF according to Van Soest (1963) methods; ether extract was determined using soxhlet extraction with gasoline after hydrolysis with 3N HCL; and GE using automatic calorimeter system (Leco AC-300, Leco Corp., St. Joseph, MI) method described in the manual at the Central Laboratory at Danish Institute of Agricultural Sciences (Hansen and Sørensen, 1996).
Statistical Analyses
Apparent digestibility for the beets or beet pulp in the diets was calculated according to Rymer (2000), assuming that the hay in diets fed in Exp. 1, 2, and 3 was digested to the same extent as in a previous experiment in which sheep were fed only hay and that there were no associative effects. Hay digestibilities and SEM measured in the previous study were as follows: 68.0 ± 0.5% for DM; 69.3 ± 0.4% for OM; 55.3 ± 0.7% for CP; 73.2 ± 0.4% for NDF; 71.3 ± 0.5% for ADF; and 65.7 ± 0.4% for DE.
Experiments were conducted as a randomized block design, so that animals were randomly assigned to one of five treatments in seven blocks for Exp. 1 and one of six treatments in seven blocks for Exp. 2 and 3. Blocks consisted of groups of adjacent digestibility crates within the facility. Data were analyzed with a two-way analysis of variance using the GLM procedures of SAS (SAS Inst., Inc., Cary NC), with treatments (feeds) and blocks (location of crates in the facility) as fixed effects. Individual treatments (beet source plant variety) were compared using least squares means, and the PDIFF option in Proc GLM was used to separate treatment means at a significance level of P < 0.05.
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Results and Discussion
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Chemical Composition
The chemical composition of the hay and fodder beet, sugar beet, and beet pulp materials for Exp. 1, 2, and 3 is shown in Table 1. Nutrient composition was similar between Roundup Ready beet varieties and pulp materials compared to their conventional counterparts, with only minor differences among the different varieties of fodder beet, sugar beet, and beet pulp tested. Aulrich et al. (2001) also reported no effect on chemical composition when the herbicide-tolerant gene (PAT gene) to glufosinate (phosphinothricin) was incorporated in sugar beet. Regardless of whether the beets were conventional or contained the glyphosate-tolerant trait, ash content varied between 4.68 and 5.88% DM for Exp. 1 and between 3.63 and 5.66% DM for Exp. 2. This relatively low ash content was likely due to the beetroots being thoroughly washed before they were cut and packaged for the experiments. French (Jarrige, 1989) and Danish (Strudsholm et al., 1997) feedstuffs tables showed an average value for total ash of 3.2 and 8.0% DM, respectively. Nitrogen content was low, as expected, and in agreement with values provided in the Danish feedstuff table, but 0.5% lower than values provided in the French table. Low N content of the beet materials resulted in the addition of urea in all diets as shown in Table 2. Ether extract (EE) varied between 0.28 and 0.49% DM for Exp. 1 and between 0.27 and 0.45% DM for Exp. 2, which is regarded as normal for fodder and sugar beet, respectively (Møller et al., 2000). Cell wall components (NDF and ADF) in fodder beet were all low compared with hay. The gross energy content of fodder beet was lower than in hay, as sugar has a lower caloric value than cell wall carbohydrates (Møller et al., 1983).
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Table 1. Chemical composition of hay and Roundup Ready and control fodder beets, sugar beets, and beet pulp derived from Roundup Ready and control sugar beets (DM basis)
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In Exp. 3, chemical composition of beet pulp was quite variable depending on the source. Crude protein (% N x 6.25) in beet pulp was within a range of 9.4 to 11.7% of DM. Neutral detergent fiber and ADF ranged from 38.8 to 50.8% of DM and 22.2 to 25.0% of DM, respectively, whereas ash and EE had ranges of 5.05 to 10.07% of DM and 0.48 to 1.27% of DM, respectively. The ash and EE contents in this experiment were similar to previous assessments that reported 2.2 to 9.4% of DM for ash and 0.45 to 1.1% of DM for EE (Iconomou et al., 1998; Mara et al., 1999; NRC, 2001).
Health and Body Weight
Throughout all three studies, no adverse health effects in sheep were observed due to the consumption of genetically modified sugar beets, fodder beets, or pulp derived from sugar beets. In Exp. 2, one sheep fed the nongenetically modified Atlantis beet was removed because of increased feed refusals. This sheep was killed and found to have chronic copper poisoning, which was unrelated to this study. In Exp. 3, one sheep fed beet pulp derived from the nongenetically modified sugar beet (Norwich, U.K.) was removed from the study because of feed refusal problems.
Based on initial and final BW of animals, all animals lost BW over the experimental periods; however, there were no significant differences in BW change among treatment groups (Table 3). Losing weight during the experimental period indicates that the feeding level may have been below the animal’s energy maintenance requirements, in combination with a possible decrease in gut fill as a consequence of changing the sheep from ad libitum feeding before the initiation of the experiments to restricted feeding. Restricted feeding was used to provide similar intakes of diets as well as to ensure there would be no feed refusals. The influence of feeding level on ruminal fill was clearly demonstrated by Robinson et al. (1987) in an experiment with dairy cows, where ruminal fill of OM was decreased from 10.7 to 3.5 kg when feed intake was reduced from ad libitum (24 kg) to a maintenance level (6 kg).
Digestibility of Nutrients in the Total Diet
Experiment 1.
Apparent digestibility of DM, OM, and DE of fodder beet were each above 80%, with no significant treatment effects (Table 4). Apparent digestibility of CP, NDF, and ADF did not significantly differ among treatments. There was a block (location within the facility) effect (P < 0.05) on ADF, but no significant treatment xblock interaction. This block effect is unexplained. Roundup Ready fodder beet A5/15 did not differ significantly in major nutrient digestibilities compared to conventional fodder beet varieties. This lack of difference in apparent digestibilities is further supported by Weisbjerg et al. (2001), who reported that there were no significant differences in milk yield, yield of energy-corrected milk, and fat, protein, and lactose milk components between Roundup Ready and conventional fodder beet varieties.
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Table 4. Apparent digestibility of nutrients in total rations containing Roundup Ready and control varieties of fodder beet in Experiment 1
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Experiment 2.
Apparent digestibility of DM, OM, CP, NDF, ADF, and DE did not differ among sugar beet treatments (Table 5). Cell wall components (NDF and ADF) were highly digestible, as the digestibility of these fractions largely exceeded 75%. Apparent digestibility of sugar was not indicated in tabular data, as no values for sugar content or digestibility of sugar were available for the hay, although it could be assumed that all sugar in the diet originated from the sugar beet materials.
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Table 5. Apparent digestibility of nutrients in total rations containing different Roundup Ready and control varieties of sugar beet in Experiment 2
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Experiment 3.
There were treatment effects (P < 0.05) for all nutrient categories in diets containing beet pulp (Table 6). Apparent digestibility of OM was greater than 80% for all treatments, whereas apparent digestibility for DM and DE in most treatments was slightly below 80%, except for the diet containing beet pulp from Belgium. Apparent digestibility of CP varied between 59.3 and 73.6%, which was in the expected range, considering the protein content of the diets fed. Cell wall components (NDF and ADF) were highly digestible, as digestibility of these fractions in most cases was greater than 80%. Apparent digestibility of the diet containing beet pulp produced from Roundup Ready sugar beet 77 fell within the range of apparent digestibility measured in sheep fed diets containing beet pulp from conventional sugar beet varieties.
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Table 6. Apparent digestibility of nutrients in total rations containing beet pulp derived from Roundup Ready sugar beet and five sources of control sugar beet pulp obtained across the European Union in Experiment 3
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Digestibility of Nutrients in Fodder Beet, Sugar Beet, and Beet Pulp
As noted previously, digestibility values for fodder beet, sugar beet, and beet pulp were calculated by difference (Rymer, 2000), assuming that the hay in diets fed in Exp. 1, 2, and 3 was digested to the same extent as in a previous experiment where sheep were fed only hay and that there were no associative effects (Tables 7, 8, and 9). Large components like DM, OM, and DE had similar SEM for digestibilities for both total diets and beet ingredients; however, smaller components, such as CP, NDF, and ADF, had larger SEM for digestibilities of beet ingredients compared with total diets, indicating greater variability for calculating these digestibilities by difference.
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Table 7. Calculated apparent digestibility of nutrients in Roundup Ready and control varieties of fodder beet in Experiment 1a
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Table 8. Calculated apparent digestibility of nutrients in Roundup Ready and control varieties of sugar beet in Experiment 2a
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Table 9. Calculated apparent digestibility of nutrients in beet pulp derived from Roundup Ready sugar beet and five sources of control sugar beet pulp obtained across the European Union in Experiment 3a
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Experiment 1.
Digestible DM and OM were above 90%, and DE was approximately 90% for different varieties of fodder beet, with no significant effects among treatments (Table 7
). Digestible OM between 92 and 94% in this experiment is close to the average value of 90% reported in feedstuff tables for fodder beet (Strudsholm et al., 1997; Jarrige, 1998), and close to values ranging from 89 to 91% reported by Søegaard and Møller (1996). No treatment effects were observed for CP, NDF, and ADF. There were no significant treatment differences in DM, OM, CP, NDF, ADF, or DE digestibilities between Roundup Ready fodder beet A5/15 and any of the conventional varieties.
Experiment 2.
Digestible DM, OM, and DE were above 90% for the different varieties of sugar beet (Table 8). Digestible OM for sugar beet varied between 94.3 to 96.6% in this experiment, which is somewhat higher than the average value of 91 and 90% reported by Jarrige (1989) and Strudsholm et al. (1997), respectively. These values are also higher than values found in a recent Danish experiment with fodder beet (Søegaard and Møller, 1996), where average values for three different years ranged from 89 to 91%. Higher values in this experiment compared with literature values may be due to higher sugar content (not measured) in these sugar beet varieties. The range in digestible DM from 91.9 to 94.9%, and the range for DE between 91.5 to 94.5% indicated only small differences among these sugar beet varieties. For CP, which makes up a small proportion of DM, digestibility is highly influenced by microbial production of this component in the rumen and also by endogenous secretion in the gut. Consequently, higher variability among treatments was observed, as expected. Digestibility of NDF and ADF was high, with nearly all values between 80 to 90%. Small and insignificant differences among sugar beet varieties in OM digestibility indicated similarity in digestibility values among other nutrient components as well. Similarity among Roundup Ready sugar beet H7-1 digestibility values with the conventional sugar beet varieties indicated that the feeding value of Roundup Ready sugar beet H7-1 was not different from the conventional varieties and, therefore, was not influenced by the genetic modification.
Experiment 3.
All digestibility values of nutrients in beet pulp derived from different sugar beet varieties showed treatment effects (P < 0.05) (Table 9). Digestible DM, OM, and DE were above 80% in all beet pulp materials, except for DM in the beet pulp sourced from England. The OM digestibilities in this experiment ranged from 85 to 89%, similar to values reported by Jarrige (1989) and Mara (1999) and in the Danish feedstuff tables (Strudsholm et al., 1997). Digestible NDF and ADF were high and between 80 and 90%, indicating that cell wall carbohydrates in beet pulp are readily fermented by microbial activity in the gut. Digestible NDF (87 to 92%) in this study was even higher than the 77% measured value in a previous study (Mara, 1999). Nutrient digestibilities in beet pulp derived from Roundup Ready sugar beet 77 had digestibility values within the range of values measured for commercial varieties indicating feeding value of the pulp made from Roundup Ready sugar beet 77 was not influenced by the genetic modification.
In conclusion, nutrient composition of Roundup Ready fodder beet, sugar beet, and beet pulp produced from Roundup Ready sugar beet 77 was similar to commercially available conventional varieties. All apparent digestibility values for the Roundup Ready beet products fell within the range of the conventional varieties tested and available literature values. Roundup Ready fodder beet, sugar beet, and beet pulp derived from Roundup Ready sugar beet evaluated in these experiments were not different in feeding value compared to commercially available beet varieties when fed to sheep.
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Footnotes
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1 We extend a special thanks to Danisco Seed for supplying the beet pulp, DLF-Trifolium for supplying the fodder beet, KWS SAAT AG for supplying the sugar beet, and to Danisco Seed, Syngenta, DLF-Trifolium, KWS SAAT AG, and Monsanto for their financial support. 
2 Correspondence: Mail Stop O3F, 800 N. Lindbergh Blvd. (phone: 314-694-8521; fax: 314-694-8575; e-mail: gary.f.hartnell{at}monsanto.com).
Received for publication May 19, 2004.
Accepted for publication November 3, 2004.
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Abstract
Introduction
