Hi,
Was she an OT horse, kept & fed 'intensively' for racing?
Cribbing is a 'coping behaviour' that horses do because they are suffering. So addressing the cause is vital, and I do not consider punishment is generally fair or reasonable if you don't - if you're not removing the motivation, IMHO, just let her do it, to find some relief. As you've found, punishing without addressing the cause is also not all that effective, and for it to be, the punishment needs to be a lot stronger than the competing motivation - so for eg the shock collar obviously wasn't strong enough - it needs to REALLY hurt her, & EVERY TIME she tries it.
Windsucking/cribbing is classed as a 'stereotypic' behaviour, meaning it's very compulsive & hard/impossible to break, even in absence of cause, once it becomes a strong habit. **It has recently been found that it may not be such an 'OCD' but that there are underlying physical issues still causing it, and some confirmed wind suckers have indeed been 'cured'.
The major cause of horses 'cribbing' is stomach ulcers or other digestive probs from not being fed adequately - too much carb/rich feed, &/or infrequent large meals &/or not enough roughage & going hungry for hrs on end. Nutritional balance has also been associated, and particularly, supplementing adequate magnesium is one of the measures said to 'cure' confirmed cribbers. Mental stress & boredom from being locked up & alone has also been long associated with the 'habit', but as lack of exercise(which effects digestion) and incorrect feeding practices generally go along with being cooped up, I'm not so sure 'mental probs' can cause it. Tho they can def. cause other health & wellbeing probs & I'd want to eliminate/minimise them regardless.
So... Firstly, great your horse is not cooped up, & free choice access to hay whenever she doesn't have grazing may help. Make sure she gets minimal if any sugary/starchy(grain for eg) feed, and that she's fed over 3-4 small meals daily, rather than 1-2 larger ones.
Treat her for ulcers. Not dead against the drugs they use - omeprazole or ranitide - but I would use herbal treatments too, like slippery elm, aloe, liquorice etc. Because the drugs only work to reduce stomach acid production, not actively heal or protect the inflamed tissue, and as such, they are only helpful for stomach ulcers & do nothing for 'hind gut' ulcers.
Ensure she's getting well balanced nutrition, with particular attention to magnesium levels. You need to do at least a basic diet analysis to work out what she's getting, to then work out what's needed to 'fill the gaps'. Dishing her up supps willy nilly is not just potentially wasteful, but can be seriously harmful. Such as...
could be a copper deficiency, so I have been adding liberal amounts of copper to her feed
Do you realise copper is a heavy metal & incredibly toxic in overdose?? It's also a substance that is not excreted, but accumulates in the liver. I hope you're doing this as part of a balanced diet(but adequate 'liberal' amounts are usually something like a small pinch of copper in the feed twice weekly), on nutritionist's/vets advice, but if not, QUIT IMMEDIATELY and consult a vet/nutritionist about countering the effects - like start adding dolomite, or other Ca/Mg supp, which is a bit of an 'antidote' to copper poisoning - tho as something that isn't excreted, it won't get rid of it from the system.
All the posts in the paddock are wooden so its perfect for cribbing, and its not practical to fence them off and to put electric wire around the tops would be very expensive.
If you're going to allow her adequate places to crib, that's not going to be helpful. Electric wire along the top is about the cheapest option to reduce her opportunity & punish her for trying.
because shes very thin and I have heard cribbing excessively can cause colic.
Any suggestions welcome! Thanks
Yes, it has commonly been thought that horses are at higher risk of colic & weightloss because of cribbing. However, that's a 'chicken & egg' thing & there have been a lot of studies showing that it is the *underlying cause* that's responsible for both colic & weightloss, not the coping behaviour that's another 'symptom' of it. One thing cribbing does tend to cause of itself though, is uneven & excessive wear of front teeth.