Why does my horse nudge me?

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Experience shapes horses behaviour 
They will change according to the responses that they receive. However bear in mind that they may not always interpret our responses in the way that we hope they will. Owners and carers have a huge influence positive or negative intentionally or accidentally. Undesirable behaviour like excessive nudging or biting is usually caused by unintentional reinforcement. So it is worth carefully considering how you plan to respond to the behaviour.
Punishment based training is no longer thought to be effective in these situations 
In fact it may even make the matter worse as well as having a significantly negative impact upon the horses welfare. Punishing the horse directly for the behaviour can cause frustration and stress for the horse as they learn what NOT to do but there is no offer of a solution or alternative for the unwanted behaviour. Positive reinforcement of the desired behaviour is usually more effective. Clicker training is an extremely useful way of training your horse to encourage the behaviours you want for example you could reward them for standing still instead of nudging. If you need help and advice on training your horse your vet may be able to help or to direct you towards a veterinary behaviourist for tailored training