He was still lame this morning, although came nearly sound after I sponged half a bucket of cold water over it. I phoned the vet for advice when they opened and they gave me the choice of either carrying on with just the cold water for 2 days and having a call out if it wasn't better or having someone out to see him today. Since I knew I'd just sit at my desk and worry about him without a second opinion (normally I'd have asked my vastly experienced neighbours, but they're away in Edinburgh) I opted for the call out and Guy duly turned up two hours later with a large cardboard box containing pretty much everything that might be needed to diagnose and treat a lame horse.
Merlin took one look at him and went 'YOU'RE THE VET WHO JABBED ME LAST SUMMER!!!' and promptly stomped off to the furthest corner of the field. Sometimes in this mood it can take me 15 minutes or so to catch him, but I'd put him in the strip grazing in the second field, so there wasn't too much space for him to mess about in and he gave in quickly with bad grace for a carrot.
Guy gave the leg a thorough check over from the shoulder to the hoof, but concluded that the problem was only in the fetlock and he'd either bashed it or strained it although there's a very, very slim outside chance it's the onset of arthritis - if it happens again that's an option that will be explored further.
Since Merlin doesn't do jabs without a twitch, Guy decided not to traumatise him and left me with instructions to give him 2 x 2 sachets of painkillers plus 1.5 sachets of antibiotics today, then another 3 days of the same dose of ABs and another 8 days (or as required) of 1 x sachet of painkillers per day. When I checked on him an hour after the first lot of painkillers he was moving MUCH more easily and this evening he was feeling well enough to trot a few paces towards a sheep that was eyeing up his supper. The swelling has gone down to the point where it's just a little bit puffy on the inside but you have to look quite hard to see the difference between the two legs.
Would it have been OK if I'd just carried on with the water? Probably, but he was obviously so much more comfortable with the painkillers in him that I think I did the right thing by getting the vet. Fingers crossed that's it sorted now and we won't need another visit.