Is it Safe to Feed Bt Corn Silage?
Commercial Bt hybrids in the market today have
shown to be equivalent to conventional hybrids. Samples are analyzed for various
parameters such as, protein, fat, fiber, starch, amino acids, fatty acids, ash, sugars,
calcium, and phosphorus to demonstrate compositional equivalence.
In addition, animal feeding studies have been done
to confirm nutritional equivalence. Results to date demonstrate that animals perform in a
comparable manner when fed biotech crops compared to their conventional counterparts.
Summary of feeding studies using corn silage or
corn stalks
- An in vitro silage study demonstrated
equivalence in digestibility and nutrient composition of Bt corn silage compared to
conventional silage (Faust, 1997,1999). Dry matter digestibility averaged 70% for the
conventional and 69.1% for the Bt hybrid (fresh and fermented). Cell wall digestibility
averaged 42.9% for the conventional and 43.8% for the Bt hybrid. Other parameters were
also measured and silages made from Bt hybrids were not different from silages made from
non-Bt near isoline hybrids when harvested at similar plant maturity.
- Green chop corn was used in a lactation study. No
differences in feed intake, milk yield, milk composition or udder health were reported for
lactating cows fed Bt or conventional green chopped whole plant corn (Faust and Miller,
1997). Researchers used green chop corn instead of fermented silage because a previous
study showed that the Cry1A (Bt) protein is degraded during the ensiling process (Fearing
et al., 1997). Therefore, the Bt protein is no longer present in the silage after
fermentation in the silo.
- An yet unpublished study showed that no DNA or Bt
protein was detected in milk samples from cows fed green chop whole plant Bt corn compared
to conventional corn. The animal digestive system degrades DNA and proteins. In this
study, again, feed intake and milk production was similar for cows fed Bt or conventional
green chop corn.
- Another study by Klotz and Einspanier (1998) could
not detect either plant DNA or transgenic DNA in cow's milk.
- Beef cows grazing Bt or conventional corn stalks had
similar performance in the first year of a two-year study. There was little difference in
the amount of hay required to maintain comparable body condition in cows grazing the crop
residues from different hybrids (Russel and Petersen, 1999).
- No differences were reported in feed intake, body
weight gain, feed conversion, hot carcass weight, dressing percentage and abdominal fat
for growing calves fed Bt or conventional corn silage (Daenicke et al., 1999).
- Conventional or Bt corn silage had similar
digestibility in sheep (Daenicke et al., 1999). Digestibility of organic matter was 75%
for conventional and 74.5% for Bt corn.
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