I buy in bulk from http://www.ostlerscidermill.co.uk/ works out about 12 quid for 5 litres. I used to use Gold Label but moved on to Ostlers. Really good service and a lovely chap to deal with.
I have been feeding it for a couple of years now but do think it helps with the shine on the coat and theoretically for joints.
Ostler's Natural Cider Vinegar is made from the freshly crushed apples from a recipe handed down through eleven generations of the Ostler family. It's use in treating numerous ailments can be traced back to Roman times and is seen by many as 'The Elixir of Life'.
Our Natural Cider Vinegar is unpasteurised and is made from freshly crushed flesh of the apples which have been allowed to mature. Non-pasteurised is literally alive. It is cloudy as it has the 'Mother' in it.
Clear cider vinegar has normally been pasteurised, which means it has been boiled to remove all the impurities to make it pretty. These clear cider vinegars you would normally find in the grocery store
I have to buy mine in the supermarket at the moment. I pay about 75p a litre. I'm hoping to find somewhere in Asturias (which is like the Spanish cider equivalent of Somerset) where I can buy unpasteurised.
I feed it for coat shine, joints and it actually seems to help with the flies in the same way garlic is supposed to.
I have just started using it to help with joints and general well being (for George that is!). I have been buying hilton herbs one which is £3 a litre so a bit pricey.
I have Charlie (16.2hh ex-racer) on 30ml a day (15ml in each feed) of Linseed oil but i'm considering changing to cider vinegar as it's pricey and i've not noticed a huge difference in coat (been on it 8 months!).