Unlike other foreign bodies that are singular in nature (splinters, for example) in this circumstance you are faced with the challenge of removing several spines from your horse, each of which cause pain upon removal. If you hurt your horse when you remove the first quill, they may resist when you try to remove the second, third, and so on.
Generally, it is best to let your vet sedate your horse and then remove multiple thorns, quills or spines. That said, you may be faced with a situation in which you must perform this skill yourself.
Study the number and placement of the quills or spines. Identify the ones you consider to be the most difficult or painful, and remove them first.
Halter the horse and have your assistant hold the horse on the same side that you are on. Make contact with the horse and, using a needle nose pliers or hemostat, grasp the quill firmly and gently pull it straight out. Do not torque or twist. The hole may bleed, which you can manage later. Now, try to move on to the second most painful quill.
After you remove one or two quills, your horse may or may not allow you to pull any more out. If this is the case, then you may need a twitch. In the rare situation you cannot use a twitch (because the quills are located in the muzzle and lip) you may need to use an ear hold.
If you are able to remove a few quills, you may take one of two paths: Continue to remove all quills because your horse is compliant. Or, take a break and give your horse a moment of relief before you return to this task. You must decide what is best for your horse given their personality and the amount of pain or discomfort they are exhibiting.
After you remove all of the quills, you will need to clean, treat and monitor the wounds for infection.
Tips for safety & Success
If you are struggling to perform this skill, leave the quills in until you get veterinary help. Removal of deeply embedded quills or thorns is extremely painful, and can be done under sedation by your vet.
For stickers of any kind that are imbedded in the limbs or body, the proper use of a twitch can be extremely helpful.
It is not true that the ends of porcupine quills need to be clipped off before the quills can be removed. It is hard enough to grasp them and get them pulled, let alone having to manipulate them twice.