78 degrees F
It is more important, however, to be CONSISTENT than it is to hit a specific number. Your livestock can adapt just fine to water temps anywhere between 76 and 83 as long as you can keep it within +/- 2 degrees over a 24 hour cycle.
Also, keep in mind that while some of your livestock will be more accustomed to temps at the higher end of that range, evaporation from the tank will increase with temperature (especially true if you live in a dryer climate).
So I'd advise you to not worry about the number itself, but choose a target that you can hit consistently based on where your tank is in your house, how you maintain the temperature in the room with the tank, what the relative humidity is where you live, etc.