Went out the game. Made no changes. Went back in and suddenly can not feed animals. See attached video. Minecraft 1.12.2. ancientwarfare-1.12.2-2.6.1.318.
https://youtu.be/3dIDOyWtm6Y

Please help.

Looks like you must have a mod that replaces wheat / carrots with something else and basically disables the vanilla items.
The logic in animal farm is simple - if items is seeds/wheat/carrot it accepts those in the food slots. So what you're trying to put in isn't vanilla wheat or carrot but something that was added by another mod.
If you can actually recreate with just AW let me know but otherwise you will have to try to figure out what mod is causing this for you.

Thanks for the prompt reply. I will go through my mods. Here is my mods list. Maybe you can give me some advice as to which mod could do this. :-) http://nellspace.co.uk/share/Minecraft%201.12.2.txt

OK. So, I found the problem to be MCMultipart mod and placeableitems mod. All good in Minecraft world now.