By Dr Charlie Blackwood

We’ve reached that time of year again when a few abortions may be seen in cows due to calve over the next few months. The first thing to remember about abortions is that a low percentage is normal. In this area, we would consider up to 2% to be well within the normal limits. To follow on from this, we usually find investigation of this low level of abortion very unrewarding. That is, we don’t identify a cause.

However, there are occasions when late abortion rates exceed these levels. If we list the most common causes identified in this area, they include Lepto, Vibrio, cypress tree poisoning, moulds, protozoa and Salmonella. The most important thing to note about this list is that the potential of at least the first 4 to cause abortion in your herd can readily be minimized.

Leptospirosis and Vibriosis

In the case of Lepto, ensuring the whole herd is vaccinated with Ultravac 7in1™ is a simple and cost effective strategy. Similarly, to safeguard against Vibrio, vaccination of all bulls with Vibrovax™ prior to commencement of the mating period is recommended. We would like to think that all our dairy farmers are doing both these things as part of their basic animal health programs.

Cypress trees

Most farms will contain some pine or cypress trees. All types of pine are potentially toxic with Macrocarpa having the worst reputation. The tree can be toxic at any stage, but wilted prunings seem to be the worst. Where cows have had access to pine trees, abortion storms often follow. These abortion cows are also highly likely to get retained membranes. Abortion can occur from day of consumption to 3 weeks later. The simple solution is to ensure cows cannot reach cypress trees in shelterbelts and to thoroughly clean up after pruning or tree lopping. It should be noted that tree loppers have been seen in the district lately.

Fungal Moulds

Moulds on hay and silage are quite common and are often identified as causes of abortion. Unfortunately, it is hard to know which are toxic and which are not. Our advice is to avoid feeding obviously mouldy or rotten hay or silage to pregnant animals.


Protozoa are parasites with a part of their life cycle involving a definitive carnivore host e.g. dogs, foxes, cats, and a part involving an intermediate host e.g. cows, sheep, humans. An example of a protozoa causing abortion in cattle is Neospora caninum. Cows become infected by eating the ‘egg’ stage, which is left on the pasture in the dung of the definitive host i.e. dogs, foxes. The involvement of dogs and foxes makes this disease difficult to control.


Salmonella can cause abortion and should be considered on farms where salmonella has occurred in the past. Once again, vaccination is available and any farmer who has had a salmonella outbreak in the past should consider its use.


Some simple ways to limit the possibility of significant rates of abortion in your herd include:

  1. Vaccinate for Lepto and Vibrio.
  2. Prevent access to all kinds of pine or cypress trees.
  3. Do not feed mouldy hay or silage to stock in late pregnancy.
  4. Consider vaccination for Salmonella on farms where out breaks have occurred.

If abortion rates are low (below 2%), there is no need to panic. If this rate rises over 2%, an abortion investigation is definitely advisable.