Host resistance to tick infestations in two breeds of goats, using the tick rhipicephalus appendiculatus neumann (the ’brown ear" tick)

Abstract

The objectives of this study were to observe and ocmpare the levels of any innate resistance and development of any acquired resistance to Fhipicephalus apoendiculatus ticks in two breeds of goats, viz. the Local East African (L.E.A.) meat goats and exotic Toggenburg (T.G.) milk goats. Ticks were applied to feed on the animal^ ears which were covered by cloth bags to prevent loss of ticks. Each day the distal ends of the ear bags were opened. Engorged ticks were collected, counted and weighed after each feeding period. The to*o groups of goats were alternately challenged with increasing burdens of both nyrnphal and adult ticks: 50 nymphs (NN) , 25 adult females (AA), 100 NN, 50AA, 200NN, 10QAA, 400NN/ 150AA and 50NN (final test) from ticks maintained in culture. Each time different rabbits, naive to R. apoendiculatus, were used as controls. They were infested at each level of challenge in order to monitor the viability of the tick culture. In all parameters measured there were no significant differences between the results from each tide test on the control rabbits indicating that the ticks were of uniform quality and the experimental results therefore were ocmparable. Feeding success of ticks, as an index of goat resistance to infestation, was assessed and found to decrease with successive tick infestations. The number of nyrnphal and adult ticks able to engorge on the goats, and their engorgement weights, decreased significantly in most cases with successive tick challenges. The duration of feeding by the attached ticks was significantly (P lengthened. The proportion of engorged nynphs that succeeded in moulting to adults decreased, while the duration of the development period increased. The pre-oviposition period for engorged female ticks was also significantly prolonged, and there was a significant reduction in mean egg output and in the percentage of eggs that hatched. Hence female ticks fed on resistant goats did experience reduced fecundity, and fertility decreased significantly. The net result was that there were far fewer larvae produced in the next generation. Responses in the two breeds of goats were significantly different in seme of the parameters. Hcwever, resistance was observed to develop in both breeds. The L.E.A. shewed greater innate resistance perhaps due to the previous history of the mothers (does) which had already encountered ticks in the field. It is likely that sane immunity against ticks was transferred to their progeny. The reduction of tick populations has important implications fran epidemiological and economic standpoints. Tick resistant goats oould be kept with cattle in order to reduce the size of the tick populations experienced by the latter. This would be a feasible irethod of biological tick control. The transmission of tick-borne diseases may also be reduced since the ability of the ticks to feed is impaired.