Well, to be honest I feel a bit confused about these responses.
Welcome to the fray!
I reckon people here are generally a good, respectful & supportive bunch. But remember, it's a world-wide forum & you'll get a heap of different opinions & assumptions from a small community, let alone this size one. What is the saying... if you ask 10 horsepeople a question, you'll get at least 20 different answers!
It's just a matter of learning all you can, to be able to weigh up the different pros & cons of different opinions.
Also don't take people's replies personally - I didn't feel any disrespect or judgement from these replies, but then I've been floating around forums, taking people the wrong way, having my own posts misunderstood...
for many years, so I have come to realise how people can understand & explain things way differently to how others may take them when we only have the written word to go on. If you feel 'attacked' or some such, it may be an occasional niggler, or someone who's... less respectful or diplomatic than most, but then again, may be just the way you perceived it.
....Now for my opinion... Sounds like dustbunny assumed you stabled your horse, as is unfortunately common in many parts. Also depending on what/how much you need to feed & what the horse has for the rest of the time, it may well be a bad move to leave the horse 'unfed' for the majority of each day. That you're not feeding grain is one thing that will give you more 'leeway' - certain foods, including grain, can be problematic, especially if not fed little & often.
If you're needing to put more weight on the horse, little & often is also best for this, so I'd be inclined to feed him over 3 meals if possible - feed him after work as well as the other 2 feeds. The more frequent, small feeds, even without adding quantity(eg. daily ration is divided into more meals), the more the horse will get out of it & the better they will do.
If the horse has adequate pasture &/or hay, has good teeth & no ulcers or such, he should do well enough without extra as a rule, although appropriate nutritional supplementation is usually a good move - the horse may also be lacking in nutrients to thrive, rather than extra calories. I wonder what did the vet say about all that - has he had his teeth attended? Did the vet suggest ulcer treatment or such? Anything else relevant the vet has said, or what he's suggested you feed?