On the Cumrbian upland farm, we had occasional inexplicable lameness in a few lambs (out of hundreds) each year. Sometimes there would be an abscess, often not. One year we had two lambs literally unable to walk, but nothing to see. Alamycin got one sorted but not the other. We started treating the lambs prophylactically for ticks every year (even though we hadn't seen ticks on them), and we never had the problem again. Might be worth introducing?