The efficacy of diminazene aceturate in three Nigerian breeds of sheep [West African Dwarf (WAD), Yankassa and Ouda] experimentally infected with Trypanosoma vivax was studied. Five rams of each breed were administered 0.5 ml of goat blood containing 2.5 × 106T. vivax per millilitre intravenously, while three rams of each breed served as uninfected controls. The treatment with diminazene aceturate was intramuscularly administered to the infected sheep, when their packed cell volume (PCV) fell to 15 %, at a dosage of 7 mg.kg−1 b. w. The parameters measured were parasitaemia, live weight gain and PCV. By 24 hours post treatment (pt.), no trypanosomes were detected by either the Haematocrit Concentration Technique (HCT) or the Polymerase Chain Reaction (PCR) in the blood of any of the treated sheep. However, a relapse of parasitaemia occurred 17 to 32 days pt. in 46.7 % of the treated rams and these were retreated with 14 mg.kg−1 b. w. diminazene aceturate. There were gradual increments in the live weight gain and the PCV of the treated rams until the resurgence of parasitaemia. Ouda had the highest cases of relapse (80 %), the least mean live weight gain and was the only breed in which mortality was recorded despite the treatment. In conclusion, diminazene aceturate administered at 7 mg.kg−1 b. w. cleared the trypanosomes in the blood of all the treated sheep within 24 hours and this was accompanied by the restoration of lost weight and the reversal of anaemia. However, the subsequent resurgence of parasitaemia indicated that a dosage of 7 mg.kg−1 b. w. was no longer reliable for complete elimination of trypanosomes from all the tissues of the host.
