Population dynamics of Rhipicephalus microplus in dairy cattle: influence of the animal categories and correlation with milk production.

Abstract

Is well known the taurine and zebuine susceptibility to Rhipicephalus microplus. Few are the reports regarding tick population dynamics between the same herd/breed, and because of this, two experiments were performed. In the 1st, the cattle tick population dynamics in dairy nursing calves (reared collective and individually), weaning calves (4-16 months), heifers (17-29 months), cows in lactation and dry cows (≥ 30 months) from the same herd, tick burden and milk production correlation were performed, for two years. R. microplus females (4.5-8.0mm) counts and the milk production were performed every 28 and 14 days, respectively. In the 2nd experiment, bovines belonging to different categories/age (newborn without previous contact with tick; 12-13 months with tick contact since birth; and 23-24 months with tick contact since birth) were experimentally infested with 30,000 R. microplus larvae, to quantify the number of fully engorged females detached from these animals. In the 1st experiment, when the mean counts of tick were ≥ 30 all animals of the group were treated. Nursing calves showed 3-4 peaks of ticks, animals reared individually showed smaller (p ≤ 0.05) tick burden than those reared collectively. Weaning calves (4-8 months) showed 5 tick peaks/year and higher mean tick burden was found than other categories. On the other hand, animals with 17-29 months of age showed smallest (p ≤ 0.05) tick burden, with 3 tick peaks/year. When the animal become lactating the tick burden increase, and 5 peaks/year occurred, and decrease again in dry cows (p ≤ 0.05) showing 4-5 tick peaks/year. Weaning calves and lactating cows received more acaricide treatments (p ≤ 0.05), 18 and 15, respectively. Nursing calves reared individually, and heifers (21-29 months) were the categories that received two acaricide treatments. The more milk the cow produce, more ticks it has (p ≤ 0.05). In the 2nd experiment, more (p ≤ 0.05) fully engorged females were recovered from younger animals than older ones. So, different tick control strategies need to be adopted in different dairy cattle categories, and the tick burden should be considered, once the effect may be more inherent to the animal rather than the strategy adopted.