There is a vast difference between a horse's digestive system, and a chicken's. A horse gets" hot " from the TDN/ total digestible nutrients, plus protein and fat in feeds that provide energy . I have always fed added corn in the winter to give them the fat and calories , and fed less in the warmer months.
A chicken stays warm from the indigestible fiber in it's feed . The crop is a fermentation vat that produces heat from breaking down that fiber, more like a ruminant. I feed less fiber ( whole grains ) in the summer. I would not feed birds beet pulp at all in the summer. It has a small amount of sugar, but is all fiber. It is used to prevent colic in horses by keeping things moving through the intestines, rather like Metamucil.
It is very hot and muggy here now. My birds are on Flockraiser , with Calf Manna, and hulled sunflower seeds added. I have birds in molt, and the trick now is to get them to consume enough protein and fat to grow nice plumage, without overheating them.The Flockraiser and the CM are ground , and require very little effort to digest, while not making gas/heat in the crop.The hulled sunflower seeds also are easier to digest than the BOSS, which I feed in the winter. The hulls of BOSS are what produce heat in the crop, while the seed kernels provide fat and energy.
My birds turn into lawnmowers when the weather turns hot too.They want the tender stuff, thank you, and follow me behind the mower eating that ,and any bugs. It looks like I'm being pursued by a flock of very portly buff egrets. They want the moisture and vitamins of the less fibrous new shoots , plus those high protein tasty bugs .Any veggies, melons etc., are high on their list too.
Feeding is an art. There is an old saying that a horse, thin at Christmas, will be a hat rack by Valentines Day. I've found it to be true. You have to adjust feeding for climate and energy expended, whether that energy is needed to stay warm , or work. It works for chickens too.