Each baby is so different. My pony filly is currently a whale and our WB colt is currently just a little under. But depending one growth spurts. He has the faintest of ribs, and when he finishes a growth spurt he fills back out and you can’t see the ribs. His coat is of good quality, and he is a happy boy.
Events in any horse’s life will cause weight fluctuations. We had a TB gelding switch pastures, and he dropped weight and condition rapidly. We upped his feed and it’s taken time but he’s almost where he was before the pasture switch. Give him another month, The weight gain is always slower than the weight loss. Week by week, stand back and evaluate him. You might not notice the difference daily. If you notice a little more spots filling out, that’s great. If not, add more grain or up his hay content. Quality hay is SO important.
We have had the greatest luck with hemp products, specifically Elite Three. It’s Canadian, but we have all of our horses on Hemp Oil and E5 Hemp Hulls, they make a worlds difference. The first time the horses eat them, they don’t like them but after a couple of days they will suck it back. Soaking is best, but the high fat content is great for putting weight on.