Effects of control of the sheep body louse (Damalinia ovis) on wool production and quality

Abstract

Groups of 35 Merino wethers under natural challenge by sheep body lice, Damalinia ovis, in south-western Queensland were subjected to four different chemical lice control treatments (arsenic, diazinon, cypermethrin and deltamethrin) over a 12-month period. Shearing took place in June. Louse populations were reduced by repeated treatments with cypermethrin. Despite high temperatures and some rainfall, populations in controls peaked at the end of summer, indicating that wool length influenced population growth. Greasy and clean fleece weights of treated sheep were higher (P<0.05) than those of controls by 0.4-1.1 kg/sheep and 0.3-0.9 kg/sheep, respectively, depending on treatment. Wool base yield was 2-45.5% higher. Sheep that were repeatedly treated with cypermethrin produced more (P<0.05) sound fleece wool (3.0 vs 1.7 kg/head greasy) and less cast fleece wool (0.1 vs 0.4 kg/head greasy) than controls. The differences in wool value between treated groups and controls ranged from $A0.45 to $A3.19 per sheep. No effect on liveweight could be attributed to treatment.