Development of a prophylactic regime using long-acting tetracycline for the control of redwater and heartwater in susceptible cattle moved into an endemic area.

Thirty young crossbred steers were purchased from a tick-borne disease-free farm in South Africa, shown to be serologically negative to Babesia bigemina/bovis and Cowdria ruminantium, and moved to an experimental farm where babesiosis and heartwater were known to be endemic. The animals were allowed to graze as a herd on tick-infested areas of the farm for 90 days from the beginning of April but were separated into three groups of 10 for treatment. One group received a prophylactic regime of two injections of 20 mg/kg of a long-acting oxytetracycline on days 7 and 14 after introduction, one received a regime of three similar injections on days 7, 14 and 21 and the other group remained untreated prophylactically. The animals were observed early each morning in a crush, rectal temperatures being taken daily and blood smears when clinical signs of disease occurred. When clinical disease was confirmed in individual animals appropriate therapeutic treatment was implemented. In addition tick counts were made weekly. All untreated control animals required treatment for redwater between days 23 and 32 and eight of them then contracted heartwater of which five died despite therapy. Four animals from the group receiving two injections of oxytetracycline and one receiving three injections also contracted redwater but rather later. During the initial 35 day assessment period it was noticed that the majority of Boophilus ticks failed to engorge on the oxytetracycline-treated animals. In the second phase of the trial theileriosis (T. mutans-type) became evident in many animals and appeared to precipitate new or recrudescent clinical redwater and heartwater in several of them.(ABSTRACT TRUNCATED AT 250 WORDS)