Very dry Spring here too and reports of higher than usual levels of joint ill and coccidiosis on lambs that've been out a pasture for around two weeks - so presumably high levels of bacteria on the pasture. If your ground has been grazed hard by horses it's likely, since they are such selective grazers, that undesirables such as buttercups, thistles, docks and nettles have spread. Old meadow that's been grazed by cattle and sheep should have a wide variety of native grasses and deep-rooted plants such as sheep's sorrel and yarrow that will withstand dry weather much better than a modern Italian rye grass and white clover ley.