If you're heating a hog barn or a broiler barn or a layer barn, there really are no options today.
You could try to incorporate some green energy to supplement that, but at this point in time, it's the propane tank hitch beside your barn, or if you're fortunate enough to have a natural gas line pass your farm, the natural gas feeds into it. Being realistic, those are the only two viable options out there today.
Electricity is always another option. It's a more expensive option, but again, there are grid restraints. For example, say in the province of Ontario, once you get past 2025, there will be a legitimately short supply of electricity, and quite likely grid capacity as well.