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.