Neospora Abortions

The average abortion rate due to Neospora has been estimated at 7% of pregnancies compared to 3% due to other causes. Abortion rates can be as high as 30% in individual herds. An economic estimate in 1998 put the cost of the disease at $24,000,000.

Abortions in our dairy herds are a common and frustrating animal health problem. The causes of abortions are numerous and most go undiagnosed. These include moldy feeds, toxins, stress and numerous infectious agents.

Neospora infections have been a common cause of bovine abortions in New Zealand over the last five to ten years. The full extent of the problem in New Zealand is undefined but the Animal Health laboratories report Neospora infections as the leading cause. The average abortion rate due to Neospora has been estimated at 7% of pregnancies compared to 3% due to other causes. Abortion rates can be as high as 30% in individual herds. An economic estimate in 1998 put the cost of the disease at $24,000,000.

Neospora occurs in all major dairying countries in the world. A recent estimated economic loss from Neospora in California alone is put at more than $US35,000,000.

Neospora infections are caused by coccidian protozoa called Neospora caninum. Neospora can infect dogs, cats, cattle, sheep goats, horses and rodents. The life cycle of the protozoa is complex and not completely understood but it appears that oocysts are excreted by a definitive host, which are then ingested by an intermediate host in which further stages of the protozoa develop. Infective material from the intermediate host is consumed by the definitive host and then the final protozoa development occurs to complete the cycle. In New Zealand the main definitive host is the farm dog and Neospora oocysts are excreted in the faeces. The main intermediate host is cattle.

In dogs the disease causes brain, peripheral nerve and muscle tissue infections. Infected intermediate hosts such as cattle rarely become ill but transplacental infections usually result in abortions or stillborn calves. Overseas studies have also shown that Neospora seropositive cows have reduced milk production following infection.

Abortion outbreaks can still occur on farms where there are no dogs. Other species such as ferrets or rodents could be involved in the spread of the disease. The high number of roaming dogs in rural New Zealand could also be an important risk factor in the spread of the disease.

In cattle most Neospora abortions occur in cows four years old or younger and most frequently occur in the fifth month of pregnancy. Neospora can be transmitted vertically, ie dam to offspring, across the placenta or in the colostrum. These infected calves may then abort when they become pregnant as rising two year olds or any later pregnancies. Direct transmission of Neospora from cow to cow is suspected to occur but has not been proven.

The good news for the control and prevention of the disease is that a vaccine has been developed by a North American company. New Zealand is the first country in the world to obtain a licence for the use of the Neospora vaccine. Intervet, a multinational pharmaceutical company, is currently carrying out trials on the vaccine in New Zealand. Hopefully the vaccine will be commercially available next dairy season. It is possible the vaccine may also improve reproductive performance in dairy herds by reducing the number of long returns and other problems associated with low conception rates.

Until the vaccine becomes available it is recommended that you do not allow dogs to defaecate on pasture that will be grazed by female cattle. If they do, then remove the faecal matter from the pasture. Dogs should not be allowed to eat any aborted calves, foetal membranes or raw beef. Keep dogs secure at night. Discourage visitors from bringing their dogs onto the farm and restrict the dogs access to the grazing pasture. Support any noxious animal control programmes in your area. Have your veterinarian investigate any abortion outbreaks this autumn and winter to see if Neospora is involved.

Kevin Rooney BVSc MACVS
Dairy Consultant Intelact Nutrition
Te Aroha Veterinary Services