Neospora: Could your Dog be a Carrier?
Dr. Arlen Mills,
Extension Veterinarian,
Capital Region, Pa.
May 31, 2002
Someone has said that dog is man’s best friend. I’m not sure that I ever believed that statement. Now with the discovery that dogs may carry a disease that can infect cows, I’m sure that better friends can be found. Dogs have been proven to be the main host and carrier of a disease agent named “Neospora caninum”.
Neospora caninum is the organism that causes the disease called “Neosporosis”. This organism is a protozoa as is the coccidia that can infect the intestine of calves. Neospora infects the intestine of the dog and is then passed in the feces of the dog to infect the feed of cows. Other members of the dog family such as the fox and coyote are also likely carriers. Eating contaminated feed infects cows and infection is life-long.
The disease caused by the coccidian parasite Neospora caninum causes abortion in the
cow. It has been found to be the most common cause of abortion in cattle in California. Testing
has shown that eighty percent of herds in Pennsylvania have Neospora infected cows.
Initial reports of Neospora suggested that abortions occurred at 4-6 months of gestation.
It is now known that infection can cause abortion or loss of the very early fetus as well. This
causes cows to miss one or two cycles and then to come back into heat. In infected herds, I see
“breeding problems” caused by these early embryonic losses, abortions in mid pregnancy, or
open cows showing up in the dry-cow pen.
Cows may eventually become pregnant and carry a calf to term. Some of these calves
will appear normal but some will show signs of brain damage. This is because the organism
infects the nervous system of the calf. Most importantly, most calves born to infected cows are
born with the infection. The only known passage of infection among cattle is this “cow to calf”
route, known as vertical transmission.
Could Neospora be causing a problem on your farm? It is only one of a multitude of
possible agents that could cause the same symptoms. Fortunately, there is a very reliable blood
test for Neosporosis. A positive result indicates that the cow has been exposed to the organism. I
recommend testing any cow that aborts and repeat breeder cows. When sending blood samples
for analysis, consider also checking for BVD, IBR, and Lepto. Labs may be able to find the
Neospora organism, in the brain of aborted calves as well.
Some interesting studies from Florida have demonstrated that cows infected with
Neospora had an 800 pound reduction in milk production per 305 day lactation. Scientists in
Texas demonstrated that calves positive for Neospora had reductions in weight gain and feed
efficiency. So Neospora infections may be costing us more than we realize.
The first step in avoiding these losses involves biosecurity practices. The most likely way
for a herd to become initially infected is through purchase of infected heifers or cows. With the
reliability of blood testing, there is no excuse for not doing prepurchase testing. If you don’t have
Neospora in your herd, don’t buy it.
If you have symptoms that could be linked to Neosporosis, have ruled out other possible
causes, and have cows test positive for the organism, you may want to consider vaccination.
Neoguard is not cheap so be sure you need it. Interestingly, calves born to vaccinated, infected
cows are protected from infection before birth so vaccination may be a way to rid a herd of the
disease. Label directions on vaccine use calls for two doses-one at pregnancy check and a second
three to four weeks later. Field use has shown however that a primary dose prebreeding followed
by two more doses as recommended has given better results.
And remember to keep the dog out of the feed bunk.
