Introducing the Bit
Before you even consider mouthing it is essential to have the teeth checked by an Equine Dentist and if necessary Wolf Teeth removed.
It is no longer common practice to use the breaking bit (Bit with Keys) - these bits were fitted and the horse left in the stable for hours on end to focus on and play with the keys. This often resulted in overactivity in the mouth and would, in many instances, encourage evasions such as drawing the tongue back and trying to put it over the bit. I do not think that the bit should ever be totally focused upon and if it is introduced correctly, it is a case of quiet relaxed, acceptance.
When I introduce the bit for the first time I use a straight bar plastic snaffle. The reason I use plastic is to avoid any accidental "clanking" on the teeth. I only have the bit attached to the headpiece and cheeks and I always have a headcollar on (remove the noseband and reins). It is wise the first few times when bridling up to unbuckle the headpiece. I would lead the horse around the stable by the leadrope attached to the headcollar and if everything is ok I would then walk the horse out in hand. As soon as the horse is confident being bitted I would then move on to the NS Starter for my long reining, lungeing, riding away, etc. This bit was designed specifically by Neue Schule for starting the babies. It is gentle and encourages the horse to stretch the topline and seek forward and down into the contact. I generally prefer the thicker starter option of 17mm as this gives more weight bearing surface across the whole of the mouth and babies are prone to losing their balance or spooking and the bit should not punish them or cause any bruising.
Figure 1: The seven points of communication. There are basically seven points of communication that the bit can work on;
1, the poll, 2, the nose, 3, the curb groove (the curb does not have to lie in the chin groove to be effective): Within the mouth; 4, the corners of the lips, 5, lower and upper bars, 6, the roof and 7, the tongue.
Figure 2: Cross section of mouth. The poll is a very sensitive area and generally very little consideration is given to this. In my experience many horses that are resistant to poll pressure are extremely happy and compliant if a padded bridle is used or you could improvise with a gel poll guard, etc. Poll sensitivity should be checked out by an Equine Physio or Osteopath.