Thank you for all your responses and apologies for the delay in getting back to you, I have been away from home for a few days.
I have in fact tried Caprivite but the goats really don't seem to like it. If I give it to them on its own, they barely touch it and if I mix it in with their muesli, it puts them off the muesli, though they will reluctantly eat a little.
I was hoping for a supplement or bolus that was long term rather than a food additive so that I didn't have to worry about daily dosing but it would appear from your comments that this is not possible. My comment on 'great expense' was in reference to large packs of commercially available bolus for cattle rather than the price of a tub of Caprivite or similar so please don't think I didn't want to 'shell out a tenner' for the sake of my babies!!!!
I have bought a variety of mineral licks in the past but the only one they have ever touched is the salt and even this is rare. I already add garlic to their feed and tried seaweed but it was met with utter refusal from both boys.
Just yesterday, I found some 'cattle and goat supplement' in the Adam Henson range.....has anyone had any experience of this? I have also emailed Brinicombe's for further info on their product so thank you for that tip.