SEASONAL DYNAMICS AND VARIATION AMONG SHEEP IN DENSITIES OF THE SHEEPBITING LOUSE, BOVICOLA-OVIS

Cyclic patterns and variations among sheep in numbers of Bovicola ovis are described in Polypay and Columbia ewes that were initially infest ed with equal numbers of lice and penned indoors continuously for 2 ye ars. Bovicola ovis populations were censused at 3-4-week intervals at 69 body sites on each animal. In the second year of the study, the ewe s were reinfested and half were mated. Louse populations were monitore d on the resulting lambs from birth until 25 weeks of age. Strong seas onal cycles in louse numbers were observed on the ewes, with peaks in spring and troughs in summer. These cycles occurred in the absence of shearing, direct solar radiation or rainfall. Populations began to dec line when daily mean and maximum temperatures were 11.5 degrees C and 15 degrees C, respectively, well below temperatures thought to cause w arm season decline. Louse densities on Polypay ewes were approximately 10 times higher than on Columbias at most inspections. There were als o large differences among sheep within breeds and sheep counts were hi ghly correlated among dates, both within and between years. One third of the ewes failed to become infested despite having lice applied on f ive separate occasions and being penned together with other infested s heep. Pregnancy and lactation did not significantly affect louse numbe rs on the ewes. There was a significant negative correlation between l ouse counts and weight gains in the lambs, and lamb counts were signif icantly correlated with those of their dams up until, but not after, w eaning. It is suggested that sheep may exert regulatory influences on lice which contribute to cycles in B. ovis populations. (C) 1998 Austr alian Society for Parasitology. Published by Elsevier Science Ltd.