Mts will be ok with co2.
You asked "Is there any livestock that is harmed by properly injected co2?" - that's the thing, Iasked about using a DIY system with no regulator and with no solenoid to connect it to a timer. I start my lights in the morning with 5 hours on, 4 hours off, 5 hours on, then off until morning. At best, I'd be disconnecting the line manually *sometime* in the evening and connecting it *sometime* in the morning. And I wouldn't be able to disconnect over the noon siesta.
So I'm not really asking about a system with properly injected co2.
I did try a search for my question but didn't find anything in the forum.