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RISK ASSESSMENT / FEED: Feeds from genetically engineered plants -Results and future challenges



------------------------------- GENET-news -------------------------------
TITLE:  Feeds from genetically engineered plants - Results and future
        challenges
SOURCE: Information Systems for Biotechnology News Report, USA
        files attached: mar07-2b.gif & mar07-2a.gif
AUTHOR: Gerhard Flachowsky
URL:    http://www.isb.vt.edu/news/2007/news07.mar.htm#mar0702
DATE:   01.03.2007
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Feeds from genetically engineered plants - Results and future challenges

The cultivation of genetically engineered plants (GEP) increased
worldwide during the last 10 years, up to about 100 million ha yearly.
Soybean, maize, rapeseed, and cotton are the predominant crops. These
plants, the so-called first generation GEP, are characterized by input
traits such as tolerance to pesticides or herbicides, or resistance
against insects. They are considered substantially equivalent to their
isogenic counterparts because they do not exhibit substantial
differences in their composition or their nutritional value.

Second generation GEP are characterized by their output traits, such as
an increase in valuable compounds (nutrient precursors, amino acids,
fatty acids, vitamins, enzymes, etc.), an improved availability of
nutrients, or a decreased concentration of undesirable substances (e.g.,
phytate, lignin, allergenic substances, etc.).

Nutritional and safety assessment of second generation GEP presents a
formidable challenge for animal nutritionists. This article reviews the
nutritional and safety assessment of feeds from first generation GEP,
and comments on the parameters for assessing second generation GEP.


Feeds from GEP with input traits (first generation)

Most GEP currently under cultivation are first generation, i.e.,
varieties without substantial changes in composition or nutritive value.
Numerous scientific associations and expert panels have proposed
guidelines for the nutritional and safety assessment of feeds from first
generation GEP (e.g., EFSA 2004, ILSI 2003). Based on these
recommendations, nutritional studies with first generation GEP feeds
have been undertaken worldwide.

Since 1997, 16 studies were performed at the Institute of Animal
Nutrition of the German Federal Agricultural Research Centre (FAL) in
Braunschweig to determine the effect of first generation GEP feeds on
the nutrition of dairy cows, growing bulls, growing and finishing pigs,
laying hens, and chickens for finishing, as well as on the growth and
laying characteristics of quail. This research was recently summarized
by Flachowsky et al. (2007).

The majority of feeds tested in the studies (e.g., Bt-maize, Pat-maize,
and Pat-sugar beet) were grown under conditions similar to their
isogenic counterparts in fields at FAL. The composition of feeds was
analysed, and animal studies were used to assess nutritional qualities,
including parameters such as digestibility, feed intake, health and
performance of target animal species, and effects on food quality
derived from the animals. Reproduction was also considered in generation
studies with quail (20 generations are now completed) and laying hens (4
generations).

Both chemical analyses and the animal studies reveal no significant
differences between GEP feeds and their isogenic counterparts (reviewed
in Table 1) and hence strongly support their substantial equivalence.
Our results agree with more than 100 studies published in the literature
and reviewed recently (Table 2).

Mycotoxin contamination of some GE crops is lower than non-GE, which may
be one exception to their substantial equivalence. For example, Bt maize
is less severely attacked and weakened by the corn borer and hence might
have a greater resistance to field infections, particularly by Fusarium
fungi, which produce mycotoxins. Evidence of reduced mycotoxin
contamination in GE crops has been demonstrated in some but not all
cases, as summarized by Flachowsky et al. (2005). In long-term studies,
numerous researchers investigated the influence of levels of corn borer
infestation of isogenic and Bt hybrids on mycotoxin contamination. Most
researchers concluded that a lower level of mycotoxin contamination was
observed in the transgenic hybrids, despite the considerable
geographical and temporal variation observed.


Feeds from GEP with output traits (second generation)

Second generation GEP are characterized by either:
an increased content of desirable/valuable traits, such as
- Nutrient precursors (e.g., b-carotene)
- Nutrients (amino acids, fatty acids, vitamins, minerals, etc.)
- Substances which may improve nutrient digestibility (e.g., enzymes)
- Substances with surplus effects (e.g., prebiotics)
- Improved sensory properties/palatability (e.g., essential oils, aromas)

or a decreased content of undesirable substances, such as
- Inhibiting substances (e.g., lignin, phytate)
- Toxic substances (e.g., alkaloids, glucosinolates, mycotoxins).

At present, detailed standardized test procedures are not generally
available to analyze feeds from second generation GEP. Possible
approaches for testing those feeds were recently reviewed by Flachowsky
and Böhme (2005). Recommendations for nutritional and safety assessment
of feeds from second generation GEP are being developed by EFSA and ILSI.

The following points should be considered when making a nutritional
assessment of second generation GEP feeds. Feeds with intended
beneficial physiological properties relating to amino acids, fatty
acids, minerals, vitamins, and other substances may contribute to higher
feed intake of animals and/or improved conversion of feed/nutrients into
food of animal origin. Furthermore, the excretion of nitrogen,
phosphorus, and other nutrients may be reduced. Consequently, depending
on the claimed difference due to the genetic modification, the
experiment must be designed to demonstrate these effects. Specific,
targeted experimental designs are necessary to show the efficiency of
the following altered nutrient constituents:

- Bioavailability or conversion of nutrient precursors into nutrients
(e.g., b-carotene).
- Digestibility/bioavailability of nutrients (e.g., amino acids, fatty
acids, vitamins).
- Efficiency of substances which may improve digestibility/availability
(e.g., enzymes, reduced phytate).
- Utilization of substances with surplus effects (e.g., prebiotics).
- Improvement of sensory properties/palatability of feed (e.g.,
essential oils, aromas).
- Lower content of undesirable substances should be demonstrated in
animal health and/or performance.

Genetic modifications may be associated with side effects (Cellini et
al. 2004), and the larger the modification, the greater the chance of
inducing secondary changes. As the basis for comparative approaches,
special animal studies seem to be necessary to examine these questions.
Therefore the nutritional and safety assessment of feeds from second
generation GEP is a significant challenge for animal nutritionists.


The fate of transgenic DNA and transgenic proteins

The consumption of feeds from GEP results in the intake of transgenic
DNA and proteins; therefore, studies were conducted on their fate within
the gastrointestinal tract of animals, and the potential to which extent
transgenes or their products may be incorporated into animal tissues.
Studies in this area were excellently reviewed recently by Alexander et
al. (2007).

Results on the fate of transgenic DNA in feeds can be summarized as followed:

- DNA is a permanent part of food/feed
(daily intake: human: 0.1 - 1 g; pig: 0.5-4 g; cow: 40-60 g).
- Transgenic (t) DNA intake amounted to ? 0.005 % of total DNA-intake,
if 50 % of the diet comes from GE crops.
- DNA is mostly degraded during conservation (silage making) and
industrial processing, as well as in the digestive tract (pH, enzymes).
- Small fragments of DNA may pass through the mucosa and may be detected
in some body tissues (especially leucocytes, liver, and spleen).
- Fragments of high-copy number genes from plants have been detected in
animal tissues to a higher extent than from low-copy numbers.
- No data exists showing that tDNA is characterized by unique behavior
compared to native plant-DNA during feed treatment and in animals.

The fate of novel proteins in feed from GEP consumed by animals has also
generated interest arising from consumers questions.

Results from studies can be summarized as follows (see also Alexander et
al., 2007):

- In ruminant feed, proteins are mostly degraded in the rumen, and
microbial and by-pass proteins are degraded by enzymes in the smaller
intestine, similar to non-ruminants.
- The chemical and physiological properties (including microbial and
enzymatic degradation) of novel proteins have been intensively tested.
- Intact novel proteins have not been detected outside of the digestive
tract in target animals (also not in animal tissues and products).
- There is no evidence that novel proteins are characterized by unusual
chemical/physical properties distinct from native protein.


Conclusions

From the data presented above, the following conclusions can be drawn:

- Presently, over 500 million hectares of GE crops have been cultivated
worldwide.
- Most animal studies have been done using first generation GE crops.
- No unintended effects in composition (except lower mycotoxins) or
nutritional assessment of feeds from first generation GE crops were
registered in any of the more than 100 studies with food producing animals.
- Novel experimental designs are necessary for the nutritional and
safety assessment of feeds from second generation GE crops.
- Transgenic DNA and novel protein do not demonstrate unique properties
during feed treatment or in animals.
- Case by case studies are necessary to answer open questions.


References

Alexander TW et al. (2007): A review of the detection and fate of novel
plant molecules derived from biotechnology in livestock production.
Anim. Feed Sci. Technol. 133, 31-62
Cellini F et al. (2004): Unintended effects and their detection in
genetically modified crops. Food Chem. Toxicol. 42, 1089-1123
EFSA (European Food Safety Authority) (2004): Guidance document of the
scientific panel on genetically modified organisms for the risk
assessment of genetically modified plants and derived food and feed.
EFSA J. 99, 1-93
Flachowsky G et al. (2007): Studies on feeds from genetically modified
plants (GMP) - Contributions to nutritional and safety assessment. Anim.
Feed Sci. Technol. 133, 2-30
Flachowsky G & Böhme H (2005): Proposals for nutritional assessments of
feeds from genetically modified plants. J. Anim. Feed Sci. 14, (Suppl.
1), 49-70
Flachowsky G et al. (2005): Animal nutrition with feeds from genetically
modified plants. Arch. Anim. Nutr. 59, 1-40
ILSI (2003): Best practices for the conduct of animal studies to
evaluate crops genetically modified for input traits. International Life
Sciences Institute, Washington, DC, 62 p., http://www.ilsi.org/file/
bestpracticescas.pdf


Gerhard Flachowsky (Director)

Institute of Animal Nutrition, Federal Agricultural Research Centre (FAL)

Bundesallee 50
38116, Braunschweig, Germany

gerhard.flachowsky@fal.de


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