Efficacy of a long-acting oxytetracycline against chlamydial ovine abortion.

The treatment of ovine abortifacient chlamydias with Terramycin/LA 200 was examined in three successive experiments in which ewes were inoculated intradermally with 6 x 10(5) PFU chlamydia at 80 days of pregnancy. The efficacy of the treatment was estimated by comparing a control group with a treated group for number of live lambs, number of abnormal lambings, length of pregnancy, average weight of lambs at birth and genital excretion of chlamydia at lambing. Sixty to eighty per cent of the ewes in the control group aborted. Under these conditions a single treatment of 20 mg/kg of Terramycin/LA at day 105 of pregnancy, i.e. four weeks after the inoculation, is not effective. On the other hand, a combination of injections, one three weeks and one five weeks after the inoculation, result in longer pregnancies on average, fewer abortions and more liveborn lambs. However, the treatment does not modify either the weight of liveborn lambs or the vaginal excretion of chlamydia at lambing. The adaptation of this treatment to practical conditions and its interest are discussed.