Just looking at your horse and seeing if you think it looks fat can be difficult when you are seeing them every day. Another way I often use to see if he has put on weight is how easily the saddle fastens up and which hole I can get it to fasten on.
I also have a weight tape that I like to use. I got this for free from Baileys Horse Feeds, I am not sure if they still give them out but it is worth sending them a message to ask! Click to go to the Baileys website! If not other feed companies may send them out. This is a good way to track your horses weight and it gives you a rough idea of what they weigh which would be very hard to estimate! A weight tape is like a tape measure to use but rather than centre-metres or inches it has what that horse weighs in kilograms. You wrap the tape around the horse's body at the withers and underneath where their girth is fastened. This can be seen on the picture below. Trooper currently weighs 484 kg which is a lot less than the start of the summer!
The weight tape around Trooper.
Another way to tell if your horse is the correct weight is by using condition scoring. There are reference diagrams to compare your horse to along with descriptions. Condition scores can be on a scale of 1-10 or more commonly 1-5. The BHS have a Condition Scoring file you can download for free telling you how to do it. Click here for the Google search and it is the top one! The images below are taken from their fact sheet.
Good condition score (3)
Fat condition score (4)
Below are some photographs of Trooper with the condition scores (before and after his weight loss regime!).
A photo of Trooper taken end of August.
A photo of trooper taken at the start of June.
The main difference I can see on trooper in these photographs is on his belly. I wish he had his head up in the photo so I could make a proper comparison but it is clear to see that he has lost weight. On the first photo, at his current weight, I would give him a condition score of 3, or maybe 3.5! But on the second photo at the start of the summer he was a condition score 4.
I am glad Trooper has lost weight now and I am sure he will be much healthier for it!