Anthelmintic resistance is when the drug no longer works because the worms have developed
a tolerance or resistance to it. Anthelmintic resistance is determined by a fecal
egg count reduction test (FECRT). Animals are weighed and treated with the anthelmintics
and fecal egg counts are conducted at the time of treatment and 7 to 14 days after
treatment. If the anthelmintic kills 90 percent or more of the worm eggs, it is considered
to be effective. If it kills 60 to 90 percent of worm eggs, it is considered to have
a moderate level of resistance. Anthelmintics killing less than 60 percent of worm
eggs are considered to have severe resistance.
The FAMACHA system monitors clinical anemia (reduction of red blood cells, packed
cell volume) by examining the color of the goat's lower eyelids and comparing it
to a color-coded chart. Variation in eyelid color from pale to red indicates the
degree of anemia. Based on this chart, only goats with anemia should be treated.
This practice will prevent the overuse of anthelmintics and consequently minimize
chances of parasite resistance to anthelmintics. The test has an effectiveness of
90 percent compared to the 20-30 percent effectiveness of overused anthelmintics.