Is this manure safe?

I have access to a large heap on a local field. Farmer says it's about 2yrs old but I wanted to test first for any nasties! Have been growing tomato seeds in a 50/50 manure and compost mix. Also in a 100% compost mix. As far as I can tell there doesn't seem to be any of the typical signs that one should look out for. What do you people think?

50/50 mix:


100% compost mix:

Thanks yorkie. Sounds like a good plan. I do recall reading somewhere that the signs can show in later growth. I'll give it another couple of weeks...