If you're riding down lanes you should expect these hazzards as they are part and parcel of the countryside. Expecting horse shit in the middle of an A road no. But on a B or C road, perfectly possible and you should be riding (as you should be driving) to the conditions and in anticipation of the hazzards. Horse shit also doesn't contain the harmfull crap that dog and cat shit does so before hassling the horse riders maybe go after the cat owners who let their moggy's shit on your gravel driveway.