Don't panic about reheating rice for chooks. They're not humans and pick up most of their food from the ground. Those minerals we like them to pick up when free ranging aren't sterile. The bacteria causing rice problems is usually Bacillus cereus and it produces two toxins if left warm. This was a problem a few years ago when restaurants/take-aways part-cooked rice in bulk, kept it warm and then finished it for service. The toxins are not destroyed by the heat of the finishing pan. If you cook properly from scratch then the bacteria are killed before they have a chance to produce toxins. Any food not eaten and stored can be contaminated so the advice is to heat to 'piping hot' (I've no idea either!) - but if it's all at 80C then all bacteria are dead. I normally make more rice than I need, freeze/refrigerate and reheat or I did before the chooks; now they get it.
If you're still worried about reheating, consider that half the hospitals in the UK use cook chill where food is cooked, chilled and reheated (they call it regeneration). It needs doing properly, but is quite safe.
One thing (amongst many) that I'm not sure about is their ability to sense heat or over hot food. I make sure that any cooked food is cooled to below skin temperature, but if they were given something too hot, would they realise before burning their mouths?