Every year when it gets a bit wet and cold several of my horses suddenly start destroying the property like there is no tomorrow! What was once a solid fence post is suddenly half the diameter in a matter of hours. Why do horses chew wood like beavers? Can you stop them?
I'm going to start with the easy question - can you stop them? Absolutely! Put metal caps over rails, run electric wires or outriggers along fence lines, use Future Posts (recycled super hard plastic), give them an abundance of hay/baleage, add a gastric conditioner to their feed or paint old diesel oil on your wood - be warned that although the diesel oil works a treat on keeping the horses from chewing you will also have the magical experience of wearing that diesel oil on your clothes every time you touch that wood forever more. Apparently drying is not something old diesel oil does.
The harder question is why? The grass at this time of year is very green and not particularly high in fibre and horses NEED to chew fibre so possibly they are looking for their fibre fix and I think this is quite possibly a big part of the problem, although there will always be that one horse that stands in his beautiful hay to eat the fence post. There does seem to be a behavioural link in that some horses are not attempting to eat their way to freedom while a group of others will systematically destroy a piece of fence as a team effort. Boredom is suggested as a cause but I find the same horses will stand in a yard sunbathing in summer but in winter they will be beavering away at nothing short of full yard destruction - I don't think they can only get bored when it's cold. Obviously there can be a nutrient deficiency but there is no research to suggest that it is one or another in particular, so you would need to get blood tests for each individual horse, or try increasing a few key vitamins/minerals to see if it helps. An uncomfortable hind gut is also a possibility so a gastric conditioner that buffers the mucosa in the stomach and the hind gut could be a fence saver and let's not forget a good pre and pro-biotic for just all round good gut health.
Personally, I add 1-2 Tbsp coarse salt to everybody's feed everyday, and believe it helps with the wood chewing, but whether to salt or not to salt is a whole other discussion. I also try to increase the hay and baleage on offer as the horses just all seem hungry in general. I decrease time in yards (so that I will still have yards come spring) and have started a couple of the worst offenders on a couple of different products. Riley is (and has been for sometime) on Maxia Complete, and is not an offender when it comes to wood chewing. Lily has just started on Tuffrock G.I. she exhibits a couple of 'ulcer' like symptoms (girthy, nappy) and is a terrible wood chewer so I will be interested to see how this one works for her. Beau is on Elite Equine's Compete, he shows no other symptoms apart from total yard demolition if left unattended! And finally, my other worst fence eating offender, Lola, will be on Dynavyte MBS. I will update on our own specific experiences in 3-4 weeks.
On an aside note, please don't google what horses and beavers have in common because the answer is that they may both be in your burger!