There are a couple ways of attempting this, and none of them are a hormone. 

If you know what you're looking for, the ingredients usually all put off a smell that is easily identifiable when used at the rates they're added. When you combine them with work, you can grow hair when you shouldn't be able to grow hair, so I have no idea if the core body temp really lowers but something is definitely going on. Is it cost affective for gain in a regular cow/calf system as they're suggesting? I doubt it, but if heat affects your breeding season a couple more calves changes things quickly.

If increasing grazing time is your priority, I think much more progress can be made via coat color and the results are verifiable by observation every single day.