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Influence of transgenic Bt176 and non-transgenic corn silage on the structure of rumen bacterial communities
Abstract
The aim of the present study was to investigate the possible effects of a diet containing transgenic corn (Zea mays), cultivar Bt176 expressing the insecticidal protein CryIA(b), on bacterial diversity of the cow rumen in vivo. Silage prepared with Bt176 corn and its parental non-transgenic cultivar showed no significant differences in either composition or in vivo degradability. Four cows were fed for 35 days with the different silage in a cross-over feeding experiment. The overall structure of rumen bacterial populations was analyzed using a cultivationindependent approach-ribosomal intergenic spacer analysis (RISA)-during 3 consecutive days of each feeding trial in all cows. Planktonic bacterial populations present in the rumen fluid and biofilm grown directly on the silage were analyzed separately. Statistical analysis of RISA fingerprints did not reveal significant differences in bacterial community structure between different feedings. Small differences were nevertheless observed between individuals on the structure of bacterial communities directly colonizing the silage material. A diet constituted by transgenic Btcorn silage was demonstrated not to be substantially different from non-transgenic corn silage in terms of composition, digestibility and impact on the overall rumen microbiota.
... 8 The safety of each GM organism must be evaluated on a caseby-case basis before being introduced to the market, 9,10 although there is extensive scientific literature available and multiple international authorities have confirmed the food or feed safety of approved GM corns. 11,12 Transgenic insect-resistant corn and transgenic herbicide-resistant corn are the most extensively cultivated GM corn varieties and have great potential for popularization in China. 1 There have been lots of feeding trials focusing on a safety evaluation of transgenic insect-resistant corn with respect to gut bacteria [13][14][15][16] and a few studoes reported no completely consistent effects on the intestinal bacteria of animals. However, most of the differences were regarded to have no negative effects on animal health. ...
... To date, research investigating the effect of feeding transgenic BT corn on gastrointestinal bacterial communities has been limited to studies in pigs and ruminants. [13][14][15][16][17][18] To our knowledge, the present study is the first to employ deep sequencing to characterize the intestinal microbiota composition of hens fed transgenic herbicide-resistant corn-based diets. ...
BACKGROUND
The present study investigated the chronic effect on the composition and proportions of the cecal microbiota of laying hens for 12 weeks after consuming two genetically modified (GM) corns containing the maroACC gene from the Agrobacterium tumefaciens strain (CC) and the mCry1Ac gene from the Bacillus thuringiensis strain (BT) in comparison with the isogenic corn (CT).
RESULTS
In total, 72 hens were randomly assigned to the CT corn‐based diet, CC corn‐based diet and BT corn‐based diet. The absolute weights of abdominal fat, breast, thigh meat and organ weight were not affected by the dietary treatment. High‐throughput 16S rRNA gene sequencing revealed a few differences in the composition of cecal microbiota among the treatments. The only difference with respect to bacterial family was that the cecal abundance of Porphyromonadaceae (3.46 versus 2.11%; P = 0.073) tended to be higher for birds consuming the CC diet than those birds consuming the CT diet. Birds fed the BT diet tended to have a higher abundance of Barnesiella (0.62 versus 0.13%; P = 0.057) and a lower abundance of unclassified Ruminococcaceae (0.64 versus 1.19%; P = 0.097) than those fed the CT diet. Considering beneficial intestinal Barnesiella, this decreases and ultimately clears the colonization of vancomycin‐resistant Enterococcus. The unclassified Ruminococcaceae was a low‐frequency and low‐abundance bacterial taxa and was not associated with intestinal pathology.
CONCLUSION
These results indicate a similar modulation of cecal microbiota in laying hens by long‐term feeding among transgenic CC corn, BT corn and non‐transgenic corn and provide data for biosafety evaluation of the transgenic corn. © 2020 Society of Chemical Industry
... Feeding the BT maize-based diet to sheep for 36 months using the bacterial culture methods did not affect the ruminal microbiota [11]. Using real-time PCR analysis or 16S rRNA gene sequencing, short-term feeding the BT maize did not affected ruminal bacterial communities of cows [12][13][14]. Although few differences in the compositions of the cecal microbiotas of pigs that were fed the BT maize diet for 31 days were observed using 16S rRNA gene sequencing, a high cecal abundance of Enterococcaceae, Erysipelotrichaceae, and Bifidobacterium, and a low abundance of Blautia were reported [15]. ...
... The intestinal microbiota plays a profound role in health and extensive research has been dedicated to the strong interplay between intestinal microbiota and host disease [2,3]. To date, research investigating the effect of feeding transgenic crops on gastrointestinal bacterial communities has been limited to studies in large intestinal and fecal microbiota [11][12][13][14][15][16], whereas the microbiota in the small intestine also has a very important effect on immune response, metabolic, and endocrine functions [17]. To our knowledge, the present study is the first to employ deep sequencing to characterize ileal microbiota composition fed the transgenic maize-based diets. ...
The experiment was to determine the chronic effects of two transgenic maize lines that contained the mCry1Ac gene from the Bacillus thuringiensis strain (BT) and the maroACC gene from Agrobacterium tumefaciens strain (CC), respectively, on ileal microbiota of laying hens. Seventy-two laying hens were randomly assigned to one of the three dietary treatments for 12 weeks, as follows: (1) nontransgenic near-isoline maize-based diet (CT diet), (2) BT maize-based diet (BT diet), and (3) CC maize-based diet (CC diet). Ileum histological examination did not indicate a chronic effect of two transgenic maize diets. Few differences were observed in any bacterial taxa among the treatments that used high-throughput 16S rRNA gene sequencing. The only differences that were observed for bacterial genera were that Bifidobacterium belong within the Bifidobacteriaceae family tended to be greater (p = 0.114) abundant in hens fed the transgenic maize-based diet than in hens fed the CT diet. Birds that consumed the CC maize diet tended to have less abundance (p = 0.135) of Enterobacteriaceae family in the ileum than those that consumed the CT maize diet. These results indicate the lack of adverse effects of the BT maize and the CC maize lines on the ileal microbiota of hens for long term and provide important data regarding biosafety assessment of the transgenic maize lines.
... Over the last few decades, culture-dependent/independent approaches, such as 16S-rRNA gene sequences, real-time PCR, ribosomal intergenic spacer analysis, and characterizing denaturing gradient gel electrophoresis bands, have been used to investigate the epiphytic microbiota in pre-ensiled crops and the microbiota in ensiled forages (Ennahar et al., 2003;Stevenson et al., 2006;Brusetti et al., 2011;Wu et al., 2014). Although the preceding studies provide information on microorganism composition in silage processes, the associated analyses only discovered a few major operational taxonomic units (OTUs) and failed to provide detailed information on microbial community composition (Ni et al., 2017). ...
Leymus chinensis is an important crop that can be fed to ruminants. The purpose of this study was to investigate the roles of Lactiplantibacillus plantarum and Lentilactobacillus buchneri in fermentation quality, aerobic stability, and dynamics of wilted L. chinensis silage microorganisms. Wilted L. chinensis silages were ensiled with/without L. plantarum and L. buchneri. After 14 and 56 days of ensiling, the silos were opened and subjected to a 7-day aerobic deterioration test. This study looked at the composition of fermentation products as well as the microbial communities in silage. Silage inoculated with L. plantarum and L. buchneri had an increased lactic acid content as well as lactic acid bacterial (LAB) quantity, but a decrease in pH and levels of butyric acid, 2,3-butanediol, and ethanol was observed during ensiling. Non-treated and L. plantarum-treated silages deteriorated in the 7-day spoilage test after opening day-14 silos, whereas L. buchneri-inoculated silage showed no signs of deterioration. Lactobacillus abundance increased in the 7-day spoilage test after opening day-56 silos, while undesirable microorganisms such as Acetobacter, Bacillus, and molds, namely, Aspergillus and Penicillium were inhibited within L. plantarum- and L. buchneri-inoculated silages. The composition of fermentation products was related to the bacterial community, particularly Lactobacillus, Enterococcus, and Acetobacter. To summarize, L. plantarum- and L. buchneri-inoculated silage enhanced fermentation quality during ensiling and inhibited aerobic spoilage in a 7-day spoilage test of 56 days ensiling within wilted L. chinensis silage.
... In the past, molecular techniques such as denaturing gradient gel electrophoresis (DGGE), real-time polymerase chain reaction (RT-PCR), and ribosomal intergenic spacer analysis (RISA) have been used to assess the microbial community in silages (Stevenson et al., 2006;Brusetti et al., 2011;Li and Nishino, 2011). However, these approaches offer limited insight regarding the overall properties of these communities. ...
We investigated the variation in microbial community and fermentation characteristics of whole-plant corn silage after treatment with lactic acid bacteria (LAB) and organic acids. The fresh corn forages were treated with a combination of L. acidophilus and L. plantarum (10 ⁶ CFU/g fresh material) or a 7:1:2 ratio of formic acid, acetic acid, and propionic acid (6 mL/g fresh material) followed by 45 or 90 days of ensiling. Silages treated with LAB showed increased lactic acid content and decreased pH after 45 days. Although treatment with LAB or organic acids decreased the common and unique operational taxonomic units, indicating a reduction in microbial diversity, the relative abundance of Lactobacillus was elevated after 45 and 90 days compared with control, which was more distinct in the organic acid groups. Moreover, we found higher levels of acetic acid and increased abundance of Acetobacter in silages treated with organic acids whereas undesirable microorganisms such as Klebsiella , Paenibacillus , and Enterobacter were reduced. In summary, the quality of corn silages was improved by LAB or organic acid treatment in which LAB more effectively enhanced lactic acid content and reduced pH while organic acid inhibited the growth of undesirable microorganisms.
... Some researchers have investigated the effects of a GM food-based diet on the composition of the faecal microbiota in laboratory rodents (Li et al., 2018) and non-human primates (Mao et al., 2016), as well as in farm animals such as cattle (Brusetti et al., 2011) and pigs (Buzoianu et al., 2012a(Buzoianu et al., , 2012b. The most recent of these studies measured the composition of faecal microbiota in Sprague-Dawley rats fed two GM maize varieties that are representative of the two major GM crop traits (herbicide tolerance, herbicide tolerance + insecticide production), in comparison with their closest isogenic maize for 10 weeks (Li et al., 2018). ...
Safety concerns arising from the consumption of foods derived from genetically modified (GM) crops remains a highly debated and controversial subject. We report here a faecal microbiota compositional analysis in Wistar rats from the GMO90+ study, which fed glyphosate-tolerant NK603 (+/− Roundup application during cultivation) and Bt toxin MON810 GM maize for 6 months (at 11 and 33% composition of the feed) in comparison to their closest non-GM isogenic lines. We first integrated the faecal microbiota compositional data with results from plasma metabolomics to establish a baseline allowing us to understand which bacterial species can influence host metabolism. Coriobacteriaceae and Acetatifactor significantly predicted plasma metabolic profile in males, while Bifidobacterium and Ruminococcus were able to predict female plasma metabolites. We then investigated the differences in fecal microbiota composition between group of rats fed MON810 or NK603 GM maize varieties in comparison to their respective isogenic lines. Bacterial community richness was not altered by the test diets. There were no statistically significant differences in taxa abundance in the rat faecal microbiota that we could attribute to the consumption of either MON810 or NK603 GM maize varieties. In conclusion, we show that the consumption of the widely cultivated GM maize varieties NK603 and MON810 even up to 33% of the total diet had no effect on the status of the faecal microbiota compared to non-GM near isogenic lines.
... Some researchers have investigated the effects of a GM food-based diet on the composition of the faecal microbiota in laboratory rodents (Li et al., 2018) and non-human primates (Mao et al., 2016), as well as in farm animals such as cattle (Brusetti et al., 2011) and pigs (Buzoianu et al., 2012a(Buzoianu et al., , 2012b. The most recent of these studies measured the composition of faecal microbiota in Sprague-Dawley rats fed two GM maize varieties that are representative of the two major GM crop traits (herbicide tolerance, herbicide tolerance + insecticide production), in comparison with their closest isogenic maize for 10 weeks (Li et al., 2018). ...
Safety concerns arising from the consumption of foods derived from genetically modified (GM) crops remains a controversial subject. We report here a faecal microbiota compositional analysis in Wistar rats from the GMO90 + study, which fed glyphosate-tolerant NK603 (+/− Roundup application) and Bt toxin MON810 GM maize for 6 months in comparison to their closest non-GM isogenic lines. We first integrated the faecal microbiota compositional data with results from plasma metabolomics to understand which bacterial species can influence host metabolism. Coriobacteriaceae and Acetatifactor significantly predicted plasma metabolic profile in males, while Bifidobacterium and Ruminococcus were able to predict female plasma metabolites. We then investigated the differences in fecal microbiota composition between group of rats fed MON810 or NK603 GM maize in comparison to their isogenic lines. Bacterial community richness was not altered by the test diets. There were no statistically significant differences in taxa abundance in the rat faecal microbiota that we could attribute to the consumption of either MON810 or NK603. We show that the consumption of the widely cultivated GM maize varieties NK603 and MON810 even up to 33% of the total diet had no effect on the status of the faecal microbiota compared to non-GM near isogenic lines.
... In the past decade, molecular tools such as denaturing gradient gel electrophoresis (DGGE), real-time PCR, terminal restriction fragment length polymorphism (TRFLP), ribosomal intergenic spacer analysis (RISA), and next generation sequencing (NGS) have been used to uncover the epiphytic microbiota in fresh forages and microbiota in ensiled forages (Stevenson et al., 2006;Brusetti et al., 2011;Li and Nishino, 2011a;Pang et al., 2011;Ni et al., 2017). However, these techniques only reflected a few of the most abundant operational taxonomic units (OTUs) present and did not reveal detailed information regarding the composition of the complete microbial community (Guo et al., 2018). ...
The present study investigated the species level based microbial community and metabolome in corn silage inoculated with or without homofermentative Lactobacillus plantarum and heterofermentative Lactobacillus buchneri using the PacBio SMRT Sequencing and time-of-flight mass spectrometry (GC-TOF/MS). Chopped whole crop corn was treated with (1) deionized water (control), (2) Lactobacillus plantarum, or (3) Lactobacillus buchneri. The chopped whole crop corn was ensiled in vacuum-sealed polyethylene bags containing 300 g of fresh forge for 90 days, with three replicates for each treatment. The results showed that a total of 979 substances were detected, and 316 different metabolites were identified. Some metabolites with antimicrobial activity were detected in whole crop corn silage, such as catechol, 3-phenyllactic acid, 4-hydroxybenzoic acid, azelaic acid, 3,4-dihydroxybenzoic acid and 4-hydroxycinnamic acid. Catechol, pyrogallol and ferulic acid with antioxidant property, 4-hydroxybutyrate with nervine activity, and linoleic acid with cholesterol lowering effects, were detected in present study. In addition, a flavoring agent of myristic acid and a depression mitigation substance of phenylethylamine were also found in this study. Samples treated with inoculants presented more biofunctional metabolites of organic acids, amino acids and phenolic acids than untreated samples. The Lactobacillus species covered over 98% after ensiling, and were mainly comprised by the L. acetotolerans, L. silagei, L. parafarraginis, L. buchneri and L. odoratitofui. As compared to the control silage, inoculation of L. plantarum increased the relative abundances of L. acetotolerans, L. buchneri and L. parafarraginis, and a considerable decline in the proportion of L. silagei was observed; whereas an obvious decrease in L. acetotolerans and increases in L. odoratitofui and L. farciminis were observed in the L. buchneri inoculated silage. Therefore, inoculation of L. plantarum and L. buchneri regulated the microbial composition and metabolome of the corn silage with different behaviors. The present results indicated that profiling of silage microbiome and metabolome might improve our current understanding of the biological process underlying silage formation.
... In recent years, to address the concern that GM foods might exert detrimental effect on gut health, then influence the overall health of the individual, a number of studies in different animal models have examined the effects of ingesting various GM foods on the bacterial communities in different parts of the gastrointestinal tract. [12][13][14][15][16][17]23,24 In line with these studies, our findings also demonstrated that GM corn lines are generally equivalent to traditional corn in terms of the impact on the general health status. Interestingly, the daily feed intakes of the rats in corn-fed groups were higher than in the standard feed group. ...
... In a study using Holstein-Friesian cows, quantitative changes in ruminal bacterial communities were analyzed by real-time PCR, and the authors concluded that diversity in microbial populations depends more on the individual animal and the sampling day than it does on the type of maize used to produce the silage consumed (Wiedemann et al., 2007). Other studies of the effects of diets containing transgenic corn on cow rumen in vivo similarly revealed no overall impact on rumen microbiota (Einspanier et al., 2004;Brusetti et al., 2011). A 3-yr longitudinal study of consumption of Bt maize in sheep likewise showed no differences and revealed no evidence of horizontal gene transfer to ruminal microorganisms or animal tissues (Trabalza-Marinucci et al., 2008). ...
Products such as meat, milk, and eggs from animals that have consumed genetically engineered (GE) feed are not currently subject to mandatory GE labeling requirements. Some voluntary “non-genetically modified organism” labeling has been associated with such products, indicating that the animals were not fed GE crops, as there are no commercialized GE food animals. This review summarizes the available scientific literature on the detection of dietary DNA and protein in animal products and briefly discusses the implications of mandatory GE labeling for products from animals that have consumed GE feed. Because glyphosate is used on some GE crops, the available studies on glyphosate residues in animal products are also reviewed. In GE crops, recombinant DNA (rDNA) makes up a small percentage of the plant’s total DNA. The final amount of DNA in food/ feed depends on many factors including the variable number and density of cells in the edible parts, the DNA-containing matrix, environmental conditions, and the specific transgenic event. Processing treatments and animals’ digestive systems degrade DNA into small fragments. Available reports conclude that endogenous DNA and rDNA are processed in exactly the same way in the gastrointestinal tract and that they account for a very small proportion of food intake by weight. Small pieces of high copy number endogenous plant genes have occasionally been detected in meat and milk. Similarly sized pieces of rDNA have also been identified in meat, primarily fish, although detection is inconsistent. Dietary rDNA fragments have not been detected in chicken or quail eggs or in fresh milk from cows or goats. Collectively, studies have failed to identify full-length endogenous or rDNA transcripts or recombinant proteins in meat, milk, or eggs. Similarly, because mammals do not bioaccumulate glyphosate and it is rapidly excreted, negligible levels of glyphosate in cattle, pig and poultry meat, milk, and eggs have been reported. Despite consumer concern about the presence of trace concentrations of glyphosate that might have been applied to feed crops and/ or the presence of rDNA or recombinant proteins in meat, milk, and eggs, the available data do not provide evidence to suggest that products from animals that have consumed approved GE feed crops differ in any distinguishable way from those derived from animals fed conventional feed or that products from animals fed GE feedstuffs pose novel health risks. © 2017 American Society of Animal Science. All rights reserved.
Lactic acid bacteria (LAB) play pivotal roles in the preservation and fermentation of forage crops in spontaneous or inoculated silages. Highlights of silage LAB over the past decades include the discovery of the roles of LAB in silage bacterial communities and metabolism and the exploration of functional properties. The present article reviews published literature on the effects of LAB on the succession, structure, and functions of silage microbial communities involved in fermentation. Furthermore, the utility of functional LAB in silage preparation including feruloyl esterase‐producing LAB, antimicrobial LAB, lactic acid bacteria with high antioxidant potential, pesticide‐degrading LAB, lactic acid bacteria producing 1,2‐propanediol, and low‐temperature‐tolerant LAB have been described. Compared with conventional LAB, functional LAB produce different effects; specifically, they positively affect animal performance, health, and product quality, among others. In addition, the metabolic profiles of ensiled forages show that plentiful probiotic metabolites with but not limited to antimicrobial, antioxidant, aromatic, and anti‐inflammatory properties are observed in silage. Collectively, the current knowledge on the roles of LAB in crop silage indicates there are great opportunities to develop silage not only as a fermented feed but also as a vehicle of delivery of probiotic substances for animal health and welfare in the future.
In this study, the comparative effects of transgenic corn (Mon 810 and Event 176) and isogenic corn (DK729) were investigated for their influence on in vitro rumen fermentation. This study consisted of three treatments with 0.25 g rice straw, 0.25 g of corn (Mon810/Event176/DK 729) mixed with 30 ml rumen fluid-basal medium in a serum bottle. They were prepared in oxygen free conditions and incubated at 39??C in a shaking incubator. The influence of transgenic corn on the number of bacterial population, F. succinogenes (cellulolytic) and S. bovis (amylolytic), was quantified using RT-PCR. Fermentative parameters were measured at 0, 2, 4, 8, 12 and 24 h and substrate digestibility was measured at 12 and 24 h. No significant differences were observed in digestibility of dry matter, NDF, ADF at 12 and 24 h for both transgenic and isogenic form of corns (p>0.05) as well as in fermentative parameters. Fluid pH remained unaffected by hybrid trait and decreased with VFA accumulation as incubation time progressed. No influence of corn trait itself was seen on concentration of total VFA, acetic, propionic, butyric and valeric acids. There were no significant differences (p
Anaerobic fungi have highly active fibrolytic enzymes and these enzymes are attractive for scientific research. We isolated
a ruminal fungus of the genusNeocallimastix sp., named GMLF7, which could survive on a variety of cellulosic material such as carboxymethylcellulose (CMC), fibrous cellulose,
avicel and wheat straw. Carboxymethylcellulase production was investigated with the above carbon sources and high CMCase activity
was obtained with CMC (73.75 U/ml), fibrous cellulose (72.68 U/ml) and avicel (70.03 U/ml). While growth temperature of the
microorganism was 39°C, for CMCase activity optimal temperature was 50°C and optimal pH 6.5. Enzyme reached maximum activity
in 60–180 min at 50°C. Substrate concentration also affected the enzyme activity which was increased more than 2 fold with
40 mg/ml CMC. Activity was measured in presence of various divalent ions and reagents, and Co2+ and DTT has a positive effect on the enzyme activity.
The identification and quantification of food ingredients based on DNA detection depends strictly on DNA stability during the food preparation treatment and on the efficiency of DNA recovery. Investigations into DNA stability carried out on polenta by real time PCR revealed that after 65 min of processing the amplifiable DNA decreased to 40% of the amount detectable before processing. Four commercial kits for DNA extraction were compared with the hexadecyltrimethyl ammoniumbromide (CTAB)-based method for DNA extraction from different maize foodstuffs: flour, canned maize, corn chip snacks, cheese corn puff snacks, chocolate corn flakes and an infant formula having a maize flour ingredient. The methods were evaluated for recovered DNA quality and yield by agarose gel electrophoresis, PCR and real time PCR targeting of the maize zein gene. No detectable DNA could be extracted from the chocolate corn flakes, whereas highly degraded DNA was extracted from all the other materials tested except flour which yielded high quality DNA. Among the methods tested, CTAB, the Wizard method and Wizard Magnetic DNA Purification System kits gave the highest DNA yields. The overall data indicate that quantitative detection of ingredients in processed food products may not reflect the original amount of DNA due to DNA degradation and low yield of DNA recovery.
A comparison was made of eight known and published PCR primer sets to detect zein, cryIA(b), bla and bar genes and the 35S cauliflower mosaic virus promoter of transgenic Bt "Maximizer" maize "event 176" (Novartis) in cooked food products. Transgenic pop corn, polenta and cookies were used as models. The polenta and cookies were made with different percentages (100, 1, 0.1% w/w) of transgenic maize flour. The DNA extracted from samples taken at different times of cooking revealed a progressive decrease in the average.
The environmental impact of transgenic plants has been questioned due to the potential persistence of proteins encoded by transgenes and horizontal gene transfer from the plant to gut microbes. The outcome of the encoded Bt [cry1A(b)] protein and transgene fragments (CaMV-35S, crylA(b), bar, and bla) was monitored in silage and processed grains of two commercial Bt11 (NK N44-P4 Bt LL and NK N27-M3 Bt LL) and one Bt176 (Elite N09-K9 Bt) corn hybrids. The three Bt-corn hybrids with their non-Bt isolines were field-grown in four replicates. Seven 1.4-kg capacity mini-silos were prepared per plot and then opened after 1, 2, 4, 8, 16, 32, and 64 d. For each hybrid, two 500-kg plastic bag silos were also prepared, sampled after 30 and 198 d, and used in a feeding trial. In the mini-silos, the transgene fragments could no longer be amplified 32 d after ensiling. In the 500-kg plastic bag silos, the transgene fragments were still detectable in the three Bt hybrid silages 30 and 198 d after ensiling. At ensiling, the Bt protein concentration was 2.69, 4.11, and 0.83 mu g g(-1) DM for the Bt hybrids N44-P4, N27-M3, and N09-K9, respectively. After 64 d of fermentation in the mini-silos, the concentration was 4, 2, and 1% of the initial concentration, respectively, but was 16, 9, and 9% after 198 d in the 500-kg silos. After stringent processing treatments, transgene fragments, except the bla gene fragment, could still be amplified from corn grains. The Bt protein concentration in corn grain of the three Bt hybrids (initially 61, 239, and 21 ng g(-1) DM, respectively) decreased by 35, 74, and 67%, respectively, after micronization, by 92, 98, and 89% after extrusion, and by 100% after flaking. After 7 d of feeding Bt corn silage to six dairy cows, Bt protein increased in ruminal digesta with higher concentrations for Bill hybrids than the Bt176 hybrid; in all cases, however, concentrations were very low in forage digesta and below detection levels in rumen fluid.
An assessment was made on the effect of inserting the cry1A(b) (Bt) gene of Bacillus thuringiensis into the genoma of two corn hybrids (the newly-developed hybrid from Cargill Semences identified as CR and the traditional B73xMo17) on the analytical composition, the in vitro rumen degradability and the mycotoxin contamination of the plant. Transgenicity changed the plant chemical composition as a function of the recipient genotype: starch was increased in the CR-Bt + plant (70.4% vs 73.3%; P < 0.10) whereas higher lignin content (6.3% vs 7.3%; P < 0.05), lower protein (7.7% vs 7.1%; P < 0.10) and soluble nitrogen (34.8% vs 26.9%; P < 0.10) contents were observed for the B73xMo17-Bt + plants. When not considering the hybrid pedigree there was a tendency (P < 0.1) toward a lower protein content in the Bt + corn seeds (9.2 vs 8.2%) and a higher sugar content in stalk and leaves (2.9% vs 5.7%). The stover degradation increased in the CRBt + variety, probably as the consequence of the higher content of lower structured carbohydrates. Transgenic plants had less ergosterol and fumonisin content than standard corn, suggesting a reduced susceptibility to mould attack.
The inhabitants of the rumen microbial eco-system, a complex consortium of different microbial groups living in symbiotic relationship with the host, act synergistically for the bioconversion of lignocellulosic feeds into volatile fatty acids which serve as a source of energy for the animals. The constraints, imposed by the host and the feed consumed by the animal, under which these microbes have to function, have been discussed. The eco-system is specialized and buffered in a narrow range of pH, which helps the animal to maintain a very well stabilized eco-system which is not disturbed by the incoming microbial contaminants into the fermentation sac (rumen) through feed and water intake. The microbial ecosystem is well studied for the rumen of domesticated animals like cattle, sheep and goat, but it is poorly studied in buffalo and wild ruminants. The necessity to use molecular biology techniques for identification and characterization of rumen microbes has been emphasized in this review.
Establishment of microbes in the young ruminant is primarily dependent upon its exposure to an adult animal and having a rumen environment compatible with growth of the microorganisms. The major portion of the rumen microbial population consists of strictly anaerobic bacteria and ciliate protozoa, which appear to account for most of the fermentative activity in this organ. Anaerobic fungi have recently been found also to be normal inhabitants of the rumen; however, they occur in lower concentrations and their ecological niche in the rumen fermentation is uncertain (Chapter 4). Microbial numbers and the composition of the population are affected by a number of factors, of which diet is probably one of the most important. Smaller numbers of facultatively anaerobic bacteria (which may be of importance in very young ruminants), aerobic bacteria, flagellate protozoa and mycoplasmas are also present; however, their contribution to the overall fermentation is considered minimal.