Really good hay and a ration balancer, or a vitamin mineral supplement in a beet pulp mash? I’m also in Canada and have no access to a good RB or anything but our two local mills feed.
I like Support One by Pureform, or Amino Trace by Mad Barn. Both VMS and Canadian companies. Mad Barn ships for free.
The thing about “energy” is that the body makes no distinction between calories for energy and calories for pudge, animal or human. However correct nutrition, enough protein, correct vitamin mineral levels, and increased fitness will give more stamina eventually.
Your description of your feed is very vague. What kind of hay? Do you get it tested? How much does he get? What’s “a scoop” of feed? What complete feed? I doubt from what you report that you have your bases covered on basic vitamins and minerals, or on protein.
When you say he is pudgy what do you mean? Could we get a photo? That can mean anything from an obese Henneke 8/10 on the edge of founder to a rather undernourished horse with a hay belly from crap hay.
Depending on what hay you have, I’d suggest upgrading to a good Timothy plus alfalfa. Also, the biggest positive change I made for my easy keeper sometimes lethargic mare was to give her more days off. I know they are “supposed” to be able to go 6 days in, one day off. She is just much more fun 4 days on, one day off.
It’s also complicated in your case by the shivers. It’s not a disease I have really read up on, but it is somewhat progressive. Many times lack of energy means a horse is feeling a bit of discomfort somewhere.