A few months ago I put my horse on a low grain diet, due to the fact that with free choice hay he was getting rather fat. I noticed recently that although he has reached a more healthy weight, he has lost a lot of mass on his back/topline. His spine now sticks out a lot, and it is especially noticeable when riding bareback. I don't want him to get fat again, but it worries me that his spine is so prominent. Any ideas on how to add volume to his back without making him fat?
He has always had free choice hay in the winter but since we have had literally no rain here, and therefore have no grass we left them on hay this year. He has always dropped weight a lot in the winter and usually puts it back on quite fast when it warms up. I show hunt seat, barrel race, and jump him which us why he gets worked so much. I cannot monitor his hay intake as he is in a pasture with other horses, and we have no where else to put him. As for saddles, I have been riding him in the same saddle for just shy of 5 years and have never had this happen before.. I will try to get a picture as soon as I can.
If he drops weight and gains it back frequently there is a good chance the saddle does not fit. A poorly fitted saddle can cause the muscles to atrophy. I would start there. Also I highly suggest getting a vet involved. Dropping a lot of weight in winter is not normal.
I just spent the whole summer struggling to get weight on my horse and build up her muscles and I had a vet involved the whole way.
How much protein is he getting as well? If you work him so much he should be on some feed supplement with high protein and fat.
No amount of feed is going to build him a good topline, unless you make him morbidly obese.
If you're not working him round - I.e. Engaging his hind legs, working into the bridle. He's not going to build topline. Trail riding, or pleasure riding, jumping etc on't do a thing if his head is stuck up in the air and quarters trailing miles out behind.
If you're riding him that much per week, then the saddle will likely have some impact, even if it fits absolutely perfectly. Any firm & unyielding pressure - like a saddle strapped into place even without a rider - can cause muscles to attrophy if in the same place long enough, due to reduced circulation. But if you've ridden in the same saddle for years without checking/adjusting it, especially if the horse has lost/gained weight, I'd say it's unlikely to fit well either, even if it did 5 years ago.
Bareback & unridden hill work is great for topline.