I'm worried and saddened by all the reports I've been reading of people whose crops have been ruined because of manure they purchased which is contaminated by a herbicide used on the grass eaten by the cows who produced the manure. A chemical in this particular herbicide 'sticks' itself to particles in the grass and is not broken down by digestion (very bad explanation see links for proper details).
This one has very good information:
And the issue is discussed at length on River Cottagehere
and It's Not Easy Being Green here
It seems that this is not just the first time this product has been involved in this kind of problem before and that something similar happened in the States a couple of years ago.