Well, it would only make sense that eating would
keep a HR up or cause it to rise a tad. The heart would have to pump a little
faster to get blood flowing to the stomach to start the digestive process. As
the horse has been moving, the stomach was "temporarily shut down" and then when
the horse stops moving, the HR drops, (hopefully) and the heart gets a
rest as do the large muscle masses that were working.
Now the horse eats, and the heart's break is over.
Back to work to get blood flowing to the stomach and start digesting. Some
horses might not have a jump in the HR, but I would guess most would. Even if
only for a minute or two.
That's why they tell us we should eat breakfast if
we want to lose weight or maintain a lower weight. Start up the metabolism. Get
the heart pumping and start burning calories.
That's what they say, anyway. I think that only
works for skinny people :)