The lamb will be reluctant to get up and move around. It may act stiff. If you force it to move around, it will gradually become less lame and stiff. If you watch it closely, it will seem to limp on one leg and then another. Its temperature will be over 104. It will usually eat if you make it get up and walk over to its feed trough.
The best treatment for this disease is the long acting tetracycline used as described for pneumonia. If sale time is within the month, however, another drug with a shorter withdrawal time should be chosen. Tylan 200 may be the best choice in that case. Check with your leader or veterinarian.