When Onix and Ramon had to be gelded, I prepared them for the vet. I know my boys well and they are not so much used to man, make that more complicated if that man is a vet who is gonna give them a shot.
They are used to the clicker system of positive reinforcement, so it was a matter of practising the ritual with an empty syringe (without the needle, needless to say…)
Vet visits can cause stress when young horses are not calm, and unfortunately bad experiences can cause the horse to get stressed for the rest of its life. That is why it is so important to practise new situations in advance with your horse. Bad imprints are difficult to erase.
If you have an older horse who is stressed with vet visits, the same procedure can be done it will just take more time. Standing still for getting shots is just one example. Everything can be practised. You can use a strange person and strange objects. The secret is to think it over and follow a shaping plan. If it takes you a week than it takes a week. If it takes a month it takes a month. If you use small steps all horses respond to be retrained. Patience will pay off.
It took me two days with 4 sessions with my boys to ensure we had no problems when the vet came and they were happy to get their shots. But they of course had no bad experiences to undo.
First step is to reward the curiosity towards the strange object, the syringe.
Second step to touch and grab their underneck, first start with one second and then building duration. While holding the syringe close. And in movement towards the horse.
Thirth step, holding their necks and pushing the syringe to the skin. Same procedure as well you want to build duration. And the horse his reactions dictate the time needed.
I really like to test the patience, and my last steps are slow, I simulate punching the skin and even searching for another place and slowly ‘inject’ It will be important that they stay calm for a longer period to be well prepared.
Let the horse be with you!