Incidence of a naturally occurring infestation by Amblyomma variegatum tick on Creole cattle and goats growth

Abstract

Five Creole heifers and 13 Creole goats suffered for a year from a naturally occurring Amblyomma variegatum infestation. Ticks were counted every two weeks on these animals and animal growth performance was compared to that of animals of the same species and numbers, raised under similar conditions, but treated every two weeks with a non remanent acaricide. ln the non treated group, Amblyomma population took several months to be constituted and animal infestation level was very variable ; 4 of the 13 goals had more than 80 % (in total weight and in adults numbers) of ail the ticks that parasitized this species during the year. Similarly, one of the 5 cattle fed half of the adult ticks. On the other hand, 4 other goals did not harbour any adult ticks during the year. The average weight of ticks (ail stages put together) fixed on the animals per day varied from 41 to 1,600 mg (mean = 609 mg) and from 3,000 to 14,700 mg (mean = 6,290 mg) for non-treated goats and cattle respectively, after one year of observation. Acaricide treatment yielded 99 % control in goats and 97 % in cattle. ln the latter species, tick infestation, which was sometimes massive (average daily tick weight = 14.7 g, 1,015 females counted during the year and a maximum of 90 females and 326 males at a given time), did not lead to a significant difference in average daily weight gain (ADWG) between untreated (ADWG = 222 g) and regularly deticked animals (ADWG = 251 g). This result confirms the speculation that Creole cattle is highly resistant to tick infestations. On the other hand, 4 of the non-treated heavily infested goats had a significantly lower ADWG (4.4 g against 37.7 g). The critical level of infestation that led to a significant fall in weight gain varied according to the time of the year from 1.6 to 11.4 fixed females per week and per animal and, probably, according to feed resources and animal intrinsic factors. During the course of the experiment, there was a progressive decrease in the effects of a given level of infestation on growth.