As nobody else has replied... we did check out a couple of companies for our horses but in the end chose to stay with our 3rd party liability cover on the house (which is miles from their field). We are allowed 5 at any one time. It may add to the premium but 50 euros a year at most.
Otherwise we do as did in the UK and pay as and when required. To date, we've been lucky, no need for vets other than for routine injections. Also no thefts from field ,fittings or minor tack. We don't leave saddle or bridles though, just in case. In general people rarely lock anything up round here in rural Aquitaine, so why would they target us? The field is over looked by several dwellings on two sides, and the lanes are rarely used by anybody who is not resident so all vehicles get noticed by somebody!
We use the EquiPassion policy with Groupama. We have anything between 12 and 20 here at any time and the policy can be tweeked to suit your specific needs. Without checking the paperwork I think ours is about 1500 euros per year.
I use Gras Savoye Hipcover. I wanted to insure my lad for castration and after trying a few others who had quoted me 300€+ JUST for a 30 day cover for death after his castration I asked my vet and she said to contact them. I contacted them, I had to take out an insurance for a year (it was same cost as everywhere else for that which I was planning on doing anyway!) but it only cost an extra 50€ to cover for death because of the castration. There is always someone to talk to and they reply quickly to emails. Obviously not needed to know whether they pay out or not, but according to the vet they do pay out quickly. I only insure for death, but their fees were reasonable for vet bills + surgery too.