The symptoms are normally the very best lamb found dead or very rarely nervous twitching , poor limb coordination followed quickly by death , no treatment . A vet may might suggest giving an anti serum to protect other lambs. The symptoms you describe sound more like gut damage from worms ( different wormer class ) or coccidiosis ( need coccidiostat ) both will show if you do a faecal egg count ( vet or sfs ) . Please react quickly as gut damage may cause very slow recovery or death , also the lambs may need oral re hydration .