My brother uses a MediDart with his cattle herd and he really likes it when no help is available to doctor a sick animal.  Here are a few links:

http://www.livestockconcepts.com/MediDart.html

http://www.farmersfarmacy.com/gc/gc_item.exe?F=D&K=696635&R=H%2FCatalog%3AInstruments%3AMedi-Dart&SN=09050100222411610815832&FF=H&FK=Catalog:Instruments:Medi-Dart&Z9

If you want to talk to him send me an email and I will get you in touch with him.