It is likely that the seed has been chemically treated to prevent rotting. You might poison the deer. Plant it instead!
If that seed is treated (more than likely if its seed corn), I don't think it'll kill the deer, but they'll have some seriously upset tummies at the very least. If its 5+ years old, I'd be willing to bet less than 10% of it germinates. The best place for that old seed corn is either in a compost pile or a dumpster somewhere.