Lots to think about here, thank you again for all your input.
I've done some more research and spoken to a different vet, so here's an update for whatever it's worth:
Decided to hold off the ABs as a first call treatment to allow an immune response to develop (but I have the Alamycin bottle at the ready will inject if there is severe deterioration and concerns about secondary infections). Topically I'm now trying an antiseptic rather than antibiotic (Leucillin, similar to Vetericyn, indicated for safe use around the eyes ). Continuing the supportive treatment with vitamins and cod liver oil to boost the immune system.
In the field where I had the original outbreak 5 weeks ago the situation seems stabilized now, no more relapses this week, and all eyes seem to be healing. The 3 worst affected ewes still have milky eyes and only partially regained their sight, but they seem back to their normal self not looking miserable or distressed. Just keeping my fingers crossed there will be no relapse. Could be that the improvement is down to just time passing, who knows...
On the other field where it broke out last week I haven't used any ABs - it's still spreading, but seems it's not affecting animals quite as aggressively. Initial recovery is slower, but no relapses so far which must be a good thing. But then I don't know yet how it will go... fingers crossed...
More bits from my research if anyone is interested:
- eye ointment with Terramycin is only available in the US it seems, and ordering it from there would incur a £35 shipping charge (so I'm not).
- I have looked into Vetericyn mentioned by [member=9755]shep53[/member] earlier on as 'worked well but very expensive'
Very expensive it is indeed and it's coming from the US too, but a bit more research brought up a cheaper UK-made product (Leucillin)mthat is based on the same hypochlorous acid technology. It's specifically indicated for safe use around eyes, and I happened to have a bottle of that around anyway, intended for wound treatment.
Can't say the effects are dramatic after two days, although those animals that I treated with it do not seem to be getting worse. With all this handling of horned sheep I ended up with a gash on my lip so I've used this stuff on myself now and can confirm it doesn't sting at all, and tastes rather like tears.