Toxoplasmosis in Sheep: The Relative Importance of the Infection as a Cause of Reproductive Loss in Sheep in Norway

The importance of toxoplasmosis as a cause of reproductive loss was examined during the period 1968—1973, based on diagnostic materials submitted from 126 flocks. Toxoplasmosis was diagnosed in 81 of these. Reliable information of the number of breeding ewes and their reproductive performance was obtained from 117 flocks, where 858 of 7812 breeding ewes failed to produce viable lambs. About 80 % of the total loss in these flocks was attributed to toxoplasmosis, 4 % to bacterial infections, and 16 % to non-infectious and/or unidentified causes.The frequency of loss within individual flocks was higher from toxoplasmosis than from any other cause, reaching a maximinn of 78 % of the breeding ewes. In 21 of 42 flocks of at least 20 breeding ewes and a high frequency of loss (≥ 10 %) from toxoplasmosis, 20 % or more of the ewes lost their lambs, whereas a loss of this order only occurred in 1 of the 13 flocks in which some other diagnosis was made.In addition to abortion, toxoplasmosis was also associated with returns to service, barrenness, stillbirth, and delivery of weak lambs that died soon after birth.White spots were observed on the cotyledons of nearly 2/3 of the placentas expelled from toxoplasmosis. No evidence was found that these changes occurred in any other disease.The incidence of abortion was higher among young ewes than among the older ones. No clinical symptoms of infection were observed prior to abortion from toxoplasmosis, and the ewes kept for breeding behaved normally in later pregnancies.