GM-free Scotland has previously raised concerns about the effects of GM crops and their associated chemicals on the health of the digestive system, in particular, its vast and vital microflora.
For example, in response to Professor Séralini's evidence of harm from eating 'NK603' GM maize and the 'Roundup' herbicide it accumulates , we noted that animals eating this maize will
“also be eating Roundup, which is known to be toxic to bacteria at very low levels. The net result can only be a change in gut microbe composition: some will be killed by the Roundup, other may thrive on elements in the transgenic maize, other might not like the NK603 at all, some will disappear because their vital companions are no longer there, and many will multiply due to the absence of the bugs which kept them in check.” 
A new study has been published which gives a perfect, concrete example of these suggested dangers.
Over the last 10-15 years, coinciding with the use of GM feed and its load of glyphosate (active ingredient of Roundup), German cattle have been suffering increased incidence of botulism-associated diseases. The bacteria which cause botulism produce a neurotoxin which can cause crippling debilitation, severe behavioural disturbances and sudden death.
In a healthy animal, gut colonisation by botulism-inducing bacteria can be prevented by the presence of 'good' bugs which generate substances to keep the bad bugs in check.
Glyphosate or Roundup residues in GM feed can change all that.
Glyphosate destroys weeds by inactivating a key cellular enzyme needed to create the building blocks of some proteins. This enzyme isn't present in animal cells, so there's nothing to inactivate there (hence the glyphosate safe-as-salt myth ), it is however a vital part of the metabolism in certain bacteria.
As a result, glyphosate can selectively knock out specific classes of microbes in the gut.
Worse, this latest research has shown that, in cattle, the bacteria harmed by glyphosate include many important 'good' bugs. And with the 'good' bugs gone, the 'bad', bugs are free to thrive.
The authors conclude that glyphosate could be a significant predisposing factor in the current increase in botulism-related disease in cattle.
They also point out that, if residue levels were high enough in food and/or water, the daily glyphosate intake accompanied by its daily attack on 'good' bugs, could be hazardous to human health too.
Glyphosate in our food and water may alter our gut microflora so as to predispose us to gastro-intestinal infections plus gut inflammation and associated nutritional disturbances. And these are only the first stage of the problem. Knock-on long-term health effects on the whole immune system, the nervous system, endocrine function and reproduction are not only possible but probable.
Glyphosate is no longer a lone player. The latest herbicide-tolerant GM crops being prepared for market have been designed for use with three different weed-killers. Your gut flora will, no doubt, be altered by all three.
Does this give you a gut-feeling that eating 100% organic food might be quite a healthy option?
 GM MAIZE IS NOT SAFE TO EAT - October 2012
 WHAT HAPPENS IN YOUR GUT WHEN YOU EAT UNSAFE GM MAIZE - October 2012
 GLYPHOSATE - SAFE AS SALT? - GMFS Archive - February 2009
- Monika Krüger et al., 2013, Glyphosate suppresses the antagonistic effect of Enterococcus spp. on Clostridium botulinum, Anaerobe 20