I know you are worried that your horse will think you are being cruel by placing a muzzle on him. And he may act bothered for a few days–or weeks. But in the end, he will adjust and it will help dramatically with his weight, with his risk for laminitis, and other ill-effects like risk of Insulin-Resistance.
Here are two examples….
16 months ago, I got a new horse–a Percheron/Standardbred X. In a couple of weeks, he had obvious odd fat-deposits develop on his body. I quickly got a muzzle, but like you, I felt guilty about him wearing it–so he only wore it for half each day. He’d run around after I put it on him, shake his head. I let it get to me. Stupid me. He got so fat even with 1/2 a day muzzle off–he never foundered, but became Insulin Resistant (IR). A pleasant horse developed behavior problems under saddle. After light work, he would buck. After much research, I found that the IR gave him pains in his belly (lactic acid buildup) after just light work. Now I had on my hands an obese horse who developed IR and couldn’t be ridden (bucking) and I could have prevented this all by having him wear the muzzle 24/7.
To fix this problem, I added magnesium to his diet, but him on a special low carb feed called M-30 (to get the nutrients needed w/o the suger, carbs and weight) and enlisted in 24/7 muzzle use. All in an effort to get his weight down. After enough weight was off him (it took over 1/2 a year and yes, he wore the muzzle through mid-December–the grass still has starches in November!), he began a retraining program in March when I was sure his IR was under control and he wouldn’t have pains in his belly when worked. At first he bucked–anticipating the pain, but then stopped with the help of several pro-riders (he had at this point developed a habit and needed to re-learn a lot). He eventually found that riding did not cause him pain.
But, I learned my lesson–this April, the muzzle went back on. When out, he wears it all the time. He is still beefy, but not obese. He no longer minds it one bit. It is just something he is used to. He gets regular exercise, and the muzzle cuts out 80% of the grass intake (compared to grazing w/o one). I like this one from Green River Tack (Tough-1 52-976 New Bright Colors Heavy Duty Poly Nylon Gazing Muzzle in neon colors–easy to find in the field). http://greenrivertack.com/catalog/product_info.php?products_id=2137&osCsid=82f07392fc1e7d210b2d8fefc686611b It is well priced at $24.50 and lasts a long while.
BTW, my pony with Cushings, also wears a muzzle 24/7 when turned out. Without it, he would not be able to walk (he gets laminitic sooooo easily).
Lastly, the second example…..A friend of mine keeps her horse 24/7 when turned out on a bare lot–no grass, and feeds a small, controlled quantity of hay. The horse just stands around–nothing to graze. This also works.
Please try the muzzle and see how many hours your horse needs to wear it to keep his weight down. Also, buy a weight tape to keep track. It really isn’t so bad and not doing so is so much worse! Hope my error helps you!