THE EFFECTS OF THE BROWN EAR-TICK, RHIPICEPHALUS-APPENDICULATUS, ON MILK-PRODUCTION OF SANGA CATTLE

Lactating Sanga cows of the Mashona breed from Zimbabwe, receiving eit her a low or a high level of nutritional supplement, were exposed to t wo levels of infestation of adults of the brown ear-tick, Rhipicephalu s appendiculatus in the highveld of Zimbabwe. The effect of the ticks on the milk yield was measured over an 11-week period during the rainy season from January to April 1986. A technique in which calves were w eighed before and after suckling was used to estimate milk yield. Ther e were significant treatment effects of ticks (P < 0.05) on milk produ ction but no significant differences in liveweight gain between calves from tick-free and tick-infested dams. The loss in milk production wa s poorly related to the number of female ticks that engorged, being 9 g (SEM 4) per tick. A Friesian x Hereford (Bos taurus) reference group of cattle carried 50% more ticks than the Mashona cows, illustrating a difference in resistance between the breeds. Thirteen screw-worm (Ch rysomya bezziana) strikes were recorded amongst the thirty-two Mashona cows compared with twenty-one amongst the ten Friesian x Hereford ani mals between January and the end of March.