Have to admit I thought the same, but since my dad was over to the house I asked him (he taught agriculture at the college level for years, managed the school farm). He can't stand Kerry but admitted that a lot of dairy farms grew their own feed. Not sure how common that would be in Massachusetts because of the cost of land there, but nonetheless... apparently not one we can nail him on.
We can still nail him on the important part: timing. He couldn't have been in Switzerland, and on a dairy farm at the same time.
In his campaign speech he said he was riding a tractor, tilling land on a dairy farm at age 12, when in fact, he was in Europe from age 11 to 13.
Also, at age 7 he moved with his parents to Washington DC, from where he went to Europe at age 11.