Bob Judd, DVM, DABVP (Equine Medicine), DABVP (Canine and Feline Practice)
Small ruminants like sheep and goats have a serious problem with intestinal parasites, but there are some management techniques you can use.
Dr. Lionel Dawson, BVSc., MS., DACT, from Oklahoma State University, says the barber pole worm (Haemonchus contortus) is the primary concern for all sheep and goats.
These intestinal parasites cause significant economic losses and are listed in the top three fatal conditions of sheep and goats. This parasite is difficult to control because it undergoes a time of halted development, a process called hypobiosis, in unfavorable weather conditions and then becomes active when the weather conditions improve.
The infective larvae on the pasture can survive up to four months, depending on the time of the year, and resistance to all classes of dewormer has been shown to some degree.
Resistance occurs when there is a less than 95% reduction in parasite eggs counted in the feces 14 days after deworming.
Resistance is related to using too low of a dose of dewormer, overusing, or rotating dewormer too frequently. It is recommended to use a FAMACHA score, which uses a chart to help identify anemia when determining which animals to deworm. A score from 1-5 is given, and the lower the score, the less anemic the animal is.
The FAMACHA score uses the color of the mucous membranes around the eyes of your sheep or goat. Animals that have less red color in their conjunctival membranes indicate they are anemic and are dewormed, and those that have dark to bright red mucous membrane color are not.
This allows some susceptible worms to remain in the animals to compete with the resistant ones. Because goats have more dewormer resistance than sheep, some veterinarians recommend combining two to three classes of different deworming medications to increase effectiveness.
For more information, ask your veterinarian about using the FAMACHA score chart to help you know when your sheep or goats need deworming.