There are two methods of euthanasia that are used in the UK: injectable and shooting. Sedation may or may not be used for both methods and is often case-dependent. The method you choose is entirely personal and should be what you are most comfortable with. All vets will counsel you on the process at the time if you choose to be present. Unfortunately, unless the horse is already lying down, both methods will result in the horse collapsing to the ground, which can be quite distressing to witness.
With injectable euthanasia, the horse is given an overdose of an anaesthetic-type medicine in the vein. The horse will lose consciousness and gently fall to the ground, with death occurring shortly afterwards.
We do not offer shooting at MBM, but we are happy to advise further over the phone if this is an option you would prefer.