Depending on where you live, livestock manure is readily available day in day out but there are only a few windows of opportunities throughout the year where you can apply raw manure on fields that are intended for human consumption.
You should never apply manure on frozen ground due to runoff issues. This is a very easy way to contaminate water and other non-targeted soils with excess nutrients and pathogens.
Raw manure that is not composted can be incorporated into the soil no less than 120 days from harvest for those crops whose edible portions have direct contact with the soil surface (carrots, lettuces, etc.)
No less than 90-days from harvest for crops whose edible portions do not have direct contact with the soil (corn.)
Manure does wonders for your crops but it is still very important to monitor soil fertility regularly to avoid manure-induced soil imbalances.