J. Dairy Sci. 88:1470-1477
© American Dairy Science Association, 2005.
Nutrient Content of Whole Cottonseed*
J. A. Bertrand1,
T. Q. Sudduth1,
A. Condon1,
T. C. Jenkins1 and
M. C. Calhoun2
1 Department of Animal and Veterinary Science, Clemson University, SC 29634
2 Texas Agricultural Experiment Station, The Texas A&M University, San Angelo 76901
Corresponding author: Jean A. Bertrand; e-mail: jbrtrnd{at}clemson.edu.
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ABSTRACT
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The objective of this study was to determine if the nutrient and gossypol contents and in vitro digestibility of 3 types of genetically modified whole cottonseed differed from traditional whole cottonseed. Samples of seed from traditional (no genetic modifications) and genetically modified varieties of cotton grown in 1999 and 2000 were analyzed. Genetic modifications included the insertion of genes to protect cotton from insect pests (Bt), and damage from glyphosate herbicides (RR), and from both (Bt/RR). Year effects were significant for in vitro dry matter (DM) digestibility, gossypol, DM, crude protein (CP), fat, neutral detergent fiber (NDF), acid detergent fiber (ADF), and ash. Higher rainfall resulted in higher CP, fat, and ash and lower NDF and gossypol. There were no differences among seed types for ground or whole seed digestibility, DM, CP, fat, NDF, ADF, ash, lignin, net energy for lactation, amino acids, total fatty acids, or seed index. Overall, the nutrient content and digestibility of varieties of genetically modified seed were similar to that of varieties of traditional whole cottonseed.
Key Words: whole cottonseed • genetically modified • gossypol • nutrient content
Abbreviation key: Bt = cotton varieties with the gene from Bacillus thuringiensis, Bt/RR = cotton varieties with both genes (Bt and RR), FA = fatty acids, IVDMD = in vitro dry matter digestibility, RR = glyphosatetolerant cotton varieties (containing the "Roundup Ready" gene), TRAD = traditional cotton varieties (no genetic modifications), WCS = whole cottonseed.
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INTRODUCTION
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Whole cottonseed (WCS) is a very popular feed for dairy cattle and is uniquely high in fiber, energy (from fat), and protein. In a nationwide survey to determine the feedstuffs fed to lactating dairy cows, it was reported that approximately 40% of dairy producers in the United States fed WCS (Mowrey and Spain, 1999). It was ranked as one of the top 5 feedstuffs used in the midwest, southeast, and southwest regions.
Recent genetic modifications have produced cotton plants more resistant to pests and tolerant to herbicides. One genetic modification includes the introduction of a gene that controls the major lepidopteran pests of cotton. The crylAc gene initially derived from a naturally occurring bacterium, Bacillus thuringiensis spp. Kurstak, has been inserted into the chromosome of cotton, enabling production of a protein that is active against the cotton bollworm, tobacco budworm, and pink bollworm (Berberich, et al. 1996). This is commonly referred to as the "Bt" gene or the "BG" gene (for BollGard, trademark of Monsanto Co., St. Louis, MO).
Another popular genetic modification is the inclusion of a cp4 epsps gene that gives tolerance to nonselective herbicides such as glyphosate (Nida et al., 1996). This cotton is known commercially as "Roundup Ready" (a trademark of Monsanto Co.) and is denoted as "RR". The inclusion of both genetic modifications is commonly called the "stacked gene" and is denoted as "Bt/RR."
In 2003, 98.7% of the cotton planted in the United States was upland cotton and 1.3% was extralong staple (pima) cotton (USDA, 2003a). The upland cotton crop planted consisted of the following genetic types: 23% traditional varieties (no genetic modifications), 2% Bt, 27% RR, and 47% Bt/RR. Therefore, transgenic cotton accounted for 77% of the cotton planted in the United States in 2003. Use of transgenic varieties ranged from a high of 100% in FL to a low of 42% in CA (USDA, 2003b).
Although these genetic modifications offer obvious advantages to the cotton grower, further research was needed to determine if the genetic modifications affected the nutrient characteristics of commercial seed. The objective of this study was to determine if the nutrient content, gossypol content, and in vitro digestibility of WCS with genetically modified traits differed from traditional WCS.
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MATERIALS AND METHODS
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Samples
Samples of WCS grown in 1999 and 2000 were obtained from the cotton variety tests at the Clemson University Edisto Research and Education Center, Blackville, SC, and at the Clemson University Pee Dee Research and Education Center, Florence, SC. Four types of seed were analyzed; samples of traditional WCS (no genetic modifications) (TRAD), those with the crylAc gene from Bacillus thuringiensis (Bt), those with the "Roundup Ready" cp4 epsps gene (RR), and those with both genes (Bt/RR) (Table 1
). For samples from 1999, 4 of the top 10 most popular varieties planted in the United States for that year were included in this study (USDA, 1999). For samples from 2000, 6 of the top 10 most popular varieties planted in the United States for that year were included in this study (USDA, 2000b).
Before analyses, samples of the whole seeds were weighed and then ground in a coffee grinder (Braun KSM 2B, Woburn, MA). The entire ground sample was then used for the analyses to prevent separation of the seed components (lint, hulls, and meats). Samples were analyzed for DM, CP, and lipid via hexane extraction (AOAC, 1990). Neutral detergent fiber and ADF were determined sequentially using an ANKOM 200/220 Fiber Analyzer (ANKOM Technology, Fairport, NY). (Note: the ADF content determined nonsequentially on a subset of 6 samples was 5.8% higher than the ADF content determined sequentially.) This equipment was also used to determine acid detergent lignin. Because of inadequate sample amounts from the 1999 samples, lignin, amino acids, and fatty acids were only determined on samples from 2000. In vitro DM digestibility (IVDMD) was determined by using an ANKOM Daisy II 200/220 Rumen Fermenter (ANKOM Technology) using rumen fluid collected from a cannulated Holstein cow consuming a diet containing WCS. Gossypol was determined at the Texas A&M University Research and Extension Center (San Angelo) using HPLC (Hron et al., 1999). Amino acids were determined on the samples from 2000 according to Moore and Stein (1963) and Hugli and Moore (1972) using an AA analyzer (Dionex, Sunnyvale, CA). Fatty acids (FA) were determined on the samples from 2000 according to Sukhija and Palmquist (1988). All laboratory analyses except gossypol were conducted using multiple replications.
To calculate the energy values in Tables 2 and 3, equations in NRC (2001) were used. Equations 2–4a, 2–4d, and 2–4e were used to calculate truly digestible nutrients. Neutral and acid detergent insoluble CP were not available for most data sets so were assumed to be zero for all data sets. The NRC (2001) recommends that the total FA content be used, when available, to calculate truly digestible fatty acids and NEL. Therefore, the actual total FA were used to calculate NEL for samples in the current study from 2000. Lignin content was not measured in Calhoun et al. (1995), NRC (1982), and NRC (1969) and was assumed to be 10%. Digestible energy at 1x maintenance was calculated using equation 2–8a, then multiplied by 0.92 to adjust for 3 x maintenance. Equations 2–10 and 2–12 were then used to calculate metabolizable energy and NEL at production levels.
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Table 2. Least square means for digestibility, nutrient, and gossypol content, and seed index of traditional and genetically modified whole cottonseed samples from 1999 and 2000.1
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Statistical analyses were performed using the GLM procedure of SAS (SAS Institute, Inc., Cary, NC) for a split-plot design. For dependent variables measured in multiple years, the main plot effects were seed type (TRAD, Bt, RR, or Bt/RR), year, and seed type x year interaction, where the main plot effects were tested by variety nested within seed type by year subclass. For independent variables measured in only one year (lignin, AA, and FA), the main plot effect was seed type, where seed type was tested by variety nested within seed type subclass. Significance was declared at P < 0.05.
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RESULTS AND DISCUSSION
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Year effects were significant for IVDMD of ground and whole seeds, gossypol, and all nutrients (Table 2
). This is presumably due to differences in weather conditions between 1999 and 2000 because cultural practices were similar. The average rainfall and temperature during the cotton growing season of 1999 was 71.8 cm and 23.9°C, and for 2000 was 54.8 cm and 24.4°C (US Weather Service, Orangeburg, SC). Subsequently, IVDMD, CP, fat, and ash, were higher and NDF and gossypol were lower in 1999, the year with higher rainfall.
The average IVDMD of ground seeds was not different among seed types and ranged from 56.1 to 60.8% (Table 2) across the 2 yr. Pena et al. (1986) reported in situ DM digestibilities of raw, extruded, and roasted cottonseed of 53.4, 48.0, and 49.5%, respectively. Though not stated, it is presumed that these samples were ground. Also, IVDMD of whole seeds was not different among seed types and ranged from 9.4% to 15.9%. Palmquist (1995) reported that 48-h in sacco digestibility of whole cottonseed was 8.4%. Low digestibility of whole seeds is due to the lack of mastication in which the seed coat is fractured and nutrients exposed.
There were no differences in nutrient content among different seed types. Contents of DM, CP, fat, NDF, ADF, lignin, ash, and NEL were not different for TRAD, Bt, RR, and Bt/RR seed types, so essentially, their feeding values are equivalent. Berberich et al. (1996) reported that seed of 2 insect-protected cotton lines were equivalent to the parental control for CP, fat, ash, carbohydrates, calories, and moisture. A third line, however, was lower in fat, higher in carbohydrates, and lower in calories when compared with seed from the control line. Nida et al. (1996) reported slight differences in CP, fat, ash, and carbohydrates in glyphosatetolerant WCS compared with the control line, but calorie content was not different. These results agree with Clark and Ipharraguerre (2001) who summarized 23 research trials and reported that genetically enhanced corn and soybeans are equivalent in nutrient composition and digestibility, and have a similar feeding value for livestock.
Gossypol, a toxic polyphenolic binaphthyl dialdehyde (Berardi and Goldblatt, 1980), exists in cotton products. Total gossypol content was not different among seed types but increased significantly from 1999 when it averaged 0.53% to 2000 when it averaged 0.74% (Table 2). The level of gossypol in seeds from 2000 was considerably higher than 0.66% reported by Calhoun et al. (1995). Nida et al. (1996) reported lower total gossypol in one line of RR WCS and higher gossypol in another line of RR WCS when compared with the parental control. Total gossypol ranged from 0.67 to 1.46% in the parental control and from 0.72 to 1.63% in the RR WCS across 2 yr of samples in that study. Berberich et al. (1996) reported similar total gossypol content in 2 Bt WCS lines compared with the parental control (1.10 and 1.08 vs. 1.16%, respectively). Total gossypol in a third line of Bt WCS was significantly lower (1.04%) than the parental control line.
Gossypol exists as a mixture of 2 stereoisomers, (+) and (–) gossypol (Calhoun et al., 1995). The minus isomer has been reported to have the greatest biological activity and is responsible for infertility in males (Matlin et al., 1985; Lindberg et al., 1987). Calhoun et al. (1995) reported that the proportions of (+) and (–) gossypol in WCS averaged approximately 60 and 40% of gossypol, respectively, in upland cotton. In our study, overall, 61.5% of the isomers were (+) and 38.6% were (–) gossypol. There were no differences in gossypol isomers among different seed types (Table 2).
Seed index, the weight (g) of 100 fuzzy seeds, is a parameter used by the cottonseed industry to monitor seed size. There were no differences in seed index among types of WCS but there was, again, a significant year effect (Table 2).
There were no differences in total fatty acid composition by seed type (Table 3). The only individual fatty acid that was significantly different among seed types was C24:0, but it comprised a very small fraction of the total FA. Linoleic acid (C18:2) was consistently present in the highest quantity and averaged 56.1% of the total FA. The FA in next highest quantity was palmitic acid (C16:0) (average = 24.0%), followed by oleic acid (C18:1), which averaged 15.2%. These were also the 3 FA in highest quantity in WCS as reported by Berberich et al. (1996) and Nida et al. (1996). Berberich et al. (1996) also reported that there were no differences in FA content among 3 lines of insect-protected WCS and their parental control line. Nida et al. (1996) evaluated 3 lines of glyphosatetolerant WCS for 2 yr and compared them with their parental control. There were no significant differences in the first year of the study (1993), but there were minor differences in one line for palmitic, oleic, malvalic (C17:0), and diyhydrosterculic acids when compared with the parental control in the second year (1994). There was also a minor difference for arachidic acid (C20:0) in another line compared with the parental line.
There were no differences in AA among different seed types (Table 4). Similar to Berberich et al. (1996), Nida et al. (1996), and Lawhon et al. (1977), glutamine, arginine, and aspartate were the 3 AA in the highest quantities. Berberich et al. (1996) reported lower levels of glutamic acid, valine, and isoleucine and higher levels of methionine, tyrosine, lysine, and histidine in 2 lines of Bt cotton compared with a third line and the parental control. Nida et al. (1996) reported no differences in AA contents of 2 lines of RR WCS compared with the parental control line.
Average contents of cysteine, valine, methionine, isoleucine, phenylalanine, histidine, and arginine were within one percentage point of values reported in NRC (2001). In contrast, leucine averaged 5.3% in our study vs. 8.6% in NRC (2001) and lysine averaged 4.3% in our study and 2.6% in NRC. Total essential AA made up 44.51% of CP in NRC (2001) and 39.2% of CP in this study.
Halle et al. (1998) reported nearly identical AA contents of Bt and nonBt corn. Sidhu et al. (2000) reported no differences in nutrient or AA composition of glyphosate-tolerant corn, a control parental line, and 5 commercial hybrids. Padgette et al. (1996) reported no differences in AA or FA content of control and glyphosate-tolerant soybeans.
Castillo et al. (2004) conducted 2 experiments that evaluated the performance of cows fed traditional and genetically modified varieties of WCS. There were no differences in either experiment for DMI, WCS intake, milk production, milk composition, or BCS. They concluded that traditional, Bt, RR, and Bt/RR varieties of WCS resulted in similar lactation performance. Hammond et al. (1996) evaluated production differences of dairy cows fed glyphosate-tolerant soybeans compared with a control line. There were no significant differences for DM, NEL, or N intakes, milk production; 3.5% FCM/NEL, percentages of protein, fat, or lactose in milk, SCC, DM digestibility, N absorbed or retained, N excreted in feces and urine, and concentration of ammonia N or molar percentages of VFA in ruminal fluid. Production of 3.5% FCM was higher for cows fed glyphosate-tolerant soybeans because milk fat content and milk yield were both slightly greater.
Table 5 compares the nutrient content of WCS from different sources reported since 1969. Although it is recognized that differences exist in laboratory procedures used to generate these results as well as differences in sample size, these historical data sets nevertheless indicate trends in nutrient content across time. These values suggest that the DM, CP, and lignin contents have remained moderately constant, the fat and ash contents have decreased, and the fiber content has increased. The change in NDF content has been the most dramatic and increased from 39.7% in 1969 (estimated from crude fiber) to 52% in the current study. Equations from NRC (2001) were used to estimate the energy content of WCS in all data sets since methods used to calculate energy content have changed. As a result of increased NDF and lignin content and decreased fat content, energy content has decreased 20% since 1969 (2.35 Mcal/kg in 1969 to 1.87 and 1.88 Mcal/kg in NRC (2001) and the current study, respectively.
These changes in nutrient content have been accompanied by a decrease in seed size for seed grown in all areas of the country except in the western United States (Figure 1), where most pima cotton is grown. The trend for reduced seed size may be related to increased selection for lint quality. In 1994, The National Cottonseed Products Association (NCPA) established a Cottonseed Quality Committee that set a goal for a minimum seed index of 10 (the weight in grams of 100 fuzzy seeds). However, seed grown in most areas of the country is smaller. Data from 2000 showed that the average seed index is less than 10 for seeds grown in all areas of the country except the western United States. Smaller seed size may result in decreased exposure to mastication and decreased seed digestibility.
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Figure 1. Seed index values (g/100 whole, linted seeds) for seed grown in 1981, 1990, and 2000 as part of the National Cotton Variety Tests, summarized by growing region: Eastern = NC, SC, GA, AL, central TN; Delta = parts of MO, AR, LA, AL, and TN surrounding the Mississippi river; Central = western LA and eastern TX; Blacklands = south central TX; Plains = OK and north central TX; Western = areas west of and including western TX. Data from USDA (1981, 1990, and 2000a).
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CONCLUSIONS
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Berberich et al. (1996) and Nida et al. (1996) evaluated the nutrient contents of lines of genetically modified WCS compared with the parent line and found negligible differences in nutrient content. Our study evaluated a large number of commercially available varieties of WCS that either had no genetic modifications or had Bt, RR, and Bt/RR gene insertions. There were essentially no differences in nutrient content, IVDMD, or gossypol content of genetically modified vs. traditional samples of upland WCS. It can be concluded, then, that there is no evidence to suggest that genetic modifications of WCS cause differences in nutrient content. Since 1969, WCS has decreased in fat and ash content and increased in fiber content, resulting in a 20% decrease in energy content. This has been accompanied by a reduction in seed size for most seed grown in the United States.
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ACKNOWLEDGEMENTS
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Gratitude is extended to Dewey Barfield for providing samples of whole cottonseed, Lloyd May at the University of Georgia for providing technical expertise, Mel Tooker, Allison Condon, Casey Lynn, Foster Wardlaw, Jr., Richard Brown, and Julie Ebenhack for assistance with laboratory analyses.
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FOOTNOTES
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* Technical contribution number 4825 of the South Carolina Agricultural Experiment Station, Clemson University. 
Received for publication May 14, 2004.
Accepted for publication November 30, 2004.
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REFERENCES
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ABSTRACT
INTRODUCTION
