2. Check where the rug lies on the withers. It should not be too far back and should sit above the withers. If it's not this high then you will have rubbed shoulders from the rug slipping down their back. You can see in the image below that the rug sits well above the withers preventing it from slipping back.
3. Once you're happy that it's done up and sitting right on the withers, check to make sure it's not too tight on the shoulders. Ideally the rug should be done up on the first or second hole on the front. If it's any looser you may find it's too tight on them and you need the next size up. . Both the straps should be done up on the same hole. Here is how the front should look:
Fouganza Stable 200 Grey £34.99
4. Next you need to check the back end. Make sure that the rug is not too long and the seam is sat in line with the top of their tail. The longer the rug the more likely it is to pull backwards on the neck (and rub), as well as additional risk factors like getting legs stuck in the leg straps and other potential injuries that might occur. If the seam is not sat above the tail then the rug is not the right length and you will need to get either a bigger size if it is above or smaller size if it is below. In the photo below can you see how the rug stops at the top of the tail, but it also sits nice and closely on the front and above the withers?
Rugs Allweather 300 brown £49.99
5. Once you're happy with that we need to look at how to adjust the straps. Firstly they must cross over the belly (front to back and back to front). Once they're done up you need to adjust them so that you can turn your hand sideways to touch both your horse's belly and the strap. Any less than this and it will be too tight, any more and they may get a leg stuck while lying down. You hand generally is no smaller than a hoof and should mean they should not be able to fit their hoof through the gap.
6. Now you just need to adjust your leg straps. These again should not be really loose or really tight. The best way to adjust them is to make sure they do not hang low, but they equally should not be touching the skin of the horse anywhere. They should hang halfway between the top of the tail and the hock, where the leg curves in as in the image below. You can either do them up as in the photo below, or you can pass them back on to the same side with one looping through the other.
If you've done all of this and you can see that they are all perfect then congratulations, you have a well fitted new rug. If it's not quite right, then work out if the problem's lie with the shape of the rug, or the adjustments that you have made. If it's the shape, then it's advised to return that rug and try another brand. Different brands fit horses differently, and if the one you picked doesn't fit your stocky cob, it might fit your narrower TB.
Feel free to contact me if you need any advice!