The prevalence of Hypoderma spp. in yaks grazed in the east of Qinghai
province was investigated in 2008. In this area, the prevalence in young yaks (1- to
3-year-old) was very high at 82.2–98.7%, whilst in adult yaks (4-year-old and older), the
prevalence was 42.4–50.6%. The seasonal development and migration pattern of
Hypoderma larvae in yak bodies was found to be similar for different
locations in this area. The numbers of first, second and third instar larvae detected in
yak bodies peaked in October, December and March, respectively. Different doses of
ivermectin (125 to 500 µg/kg body weight) almost completely dewormed the
larvae from yaks, suggesting that using a quarter of the prescribed dose (500
µg/kg body weight) was effective. In October of each year between 2009
and 2012, ivermectin (125 µg/kg body weight) was administered to a total
of 562,995 yaks grazed in four counties in Qinghai province, and the pevalence of
Hypoderma larval infection in yaks was reduced to 0.5–1.0%.