EFFECTS OF TICK INFESTATION AND TICK-BORNE DISEASE INFECTIONS (HEARTWATER, ANAPLASMOSIS AND BABESIOSIS) ON THE LACTATION AND WEIGHT-GAIN OFMASHONA CATTLE IN SOUTH-EASTERN ZIMBABWE

The effects of ticks and tick-borne disease infections on the lactatio n and weight gain of Mashona cattle were studied at Mbizi Quarantine S tation in the south-eastern lowveld of Zimbabwe. Twenty-nine Mashona c ows were allocated to 2 balanced groups and kept in separate paddocks at a stocking rate of one animal per 8 ha. One group received regular acaricide treatment to control bont (Amblyomma hebraeum) and other tic ks, The other group was left untreated. The cows were artificially ins eminated. The acaricide-treated cows and calves were essentially tick free throughout the experiment, while the untreated cows and calves we re continuously tick infested. There was a drought-related decline in tick infestations in the second year of the experiment. Antibodies to Cowdria ruminantium, Babesia bigemina and Anaplasma marginale were det ected in cows and calves from both groups, though the untreated group had significantly higher titres to C. ruminantium (P < 0.001). The tot al, measured amount of milk suckled by untreated calves was significan tly more than treated calves (273 kg vs. 241 kg, P less than or equal to 0.05). By interpolating between the twice weekly measurements, it w as calculated that over the entire lactation untreated calves stickled an average of 935 kg/hd vs. 837 kg/hd for the treated group. There we re no statistical differences in the weights of the 2 groups of calves at birth, weaning, 180 and 210 days post partum (P < 0.05). For cows, there were no statistically significant differences in gestation peri ods (288 vs. 279 days), reconception rates or weight patterns over rim e (P < 0.05). The results show that intensive acaricide treatment in a reas of Zimbabwe where heartwater is enzootically stable is uneconomic al. The maintenance of enzootic stability for tick-borne diseases thro ugh minimal tick control is clearly a more economic and practical cont rol option.