livestock Plan ahead


to beat Toxoplasmosis


by Stephen Kenyon, Technical Director, Strathclyde Nutrition


Toxoplasmosis is one of the main causes of abortion in sheep and it results from a Toxoplasma gondii infection. Toxoplasmosis gondii is capable of infecting all warm blooded animals, including man. In this article we attempt to review the lifecycle of the parasite and discuss practical methods of control.


There are three stages in the parasite’s life cycle. The cat is central to the life-cycle of the parasite and infected cats shed large numbers of oocysts in their faeces. These oocysts are very hardy and can survive in the environment for many months contaminating pasture, feed and water and are the source of infection in livestock. Sheep are most likely to become infected with Toxoplasma through the ingestion of oocysts and disease is mainly observed if infection occurs for the first time during pregnancy. The severity of the disease is related to the gestational age of the foetus and its subsequent ability to resist infection. The younger the foetus, the more vulnerable it is to attack by Toxoplasma. If toxoplasma infection occurs early in pregnancy the likely outcome is foetal death and reabsorption, leaving a barren ewe.


The immune system of the foetus develops as the pregnancy progresses making it progressively more able to fight against the invading parasite and infection around mid-pregnancy may typically result in production of a weak or still-born lamb, often accompanied by a small mummified foetus. These weak lambs may only survive for a few days after birth. Infection in late pregnancy usually results in birth of viable lambs with no obvious clinical signs, although they may be carrying the infection which is kept in check by their immune defence system. Following infection and/or abortion due to toxoplasma parasites,


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