Host Resistance To Tick Infestations In Two Breeds Of Goats, Using The Tick Rhip. Icephalus Appendiculatus Neumann (the "brown Ear" Tick).
The objectives of this study were to observe and compare the levels of any innate resistance and development of any acquired resistance to Rhipicephalus appendiculatus ticks in two 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 animals ears whichwere 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 two groups of goats were alternately challenged with increasing burdens of both nymphala, and adult ticks: 50 nymphs (NN) 25 adult females (AA}. 100 NN, SAA,. 2ONN, 10AA, 4ONN, 150AA and 50NN (final test) from ticks maintained in culture. Each time different rabbits, naive to R. appendiculatus, 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 reresults from each tick test on the control rabbits indicating that; the ticks were of uniform quality and the experimental results therefore were comparabIe , 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 nymphal,and adult ticks able to engorge on the goats, and their engorgerrentweights, decreased significantly in most cases with successive tick challenges. The duration of feeding by the attached ticks was significantly (p<0.(01) Lencrthened, The proportion of engorged nymphs 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 (p<o .001) 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 some of the parameters. However,resistance was observed to develop in both breeds. TheL.E.A. showedgreater innate resistance perhaps due to the previous history of the mothers (does) which had already encuntered ticks in the field. It is likely that sore immunity against ticks was transferred to their progeny. The reduction of tick populations has important implication from epidemiological and economic standpoints. Tick resistant goats could be kept with cattle in order to reduce the size of the tick populations experienced by the latter. This would be a feasible method of biological tick oontrol. The transmission of tick-borne diseases may also be reduced since the ability of the ticks to feed is impaired.