When did you plant the oats? Was anything else sprayed in the plot? Did the oats look like they were being grazed/plucked, or where they turning brown and shriveling up? What, if any, weeds do you still have growing?
It could very well be that deer and turkeys ate the whole plot, especially if you do not have other food sources in the immediate area. Sounds like you did things just fine, and oats are rather easy to grow.