News & Advice

Are your pregnancy rates not what you expect?

Apr 5, 2018 | Beef cattle, Bulls, Dry stock

There are three reasons for low in-calf rates; poor bull fertility, poor conception rates or high embryonic loss. I’ll talk about the third cause in this article (though the last two are sometimes linked) and we will cover the others in coming months.

High embryonic loss in cattle is defined as more than 5% loss, as some sporadic loss is normal. If you are concerned about your empty rate, the first thing we need to figure out is where the losses are occurring.
We recommend scanning the cows 6-8 weeks after the bull out for several reasons. This is the ideal time for scanning (later pregnancies often have to be manually palpated) so that you are not grazing empty cows longer than necessary, and to help us pick up abortion storms (either before or after scanning).

In New Zealand the infectious causes of abortion can be split into Bacterial, Viral, Protozoal and Fungal, and a few of the most common diseases are:


  • Leptospirosis can result in sick cows, milk drop, abortions, weak calves, anaemia and jaundice. This is less common now due to widespread vaccination programs but still a risk where cattle are in contact with pigs, or where herds are unvaccinated. Infected cows shed high numbers of Leptospira in urine and so it is highly infectious. Abortion normally occurs 4 to 12 weeks after infection, so it can be difficult to diagnose.
  • Salmonella – abortion due to salmonella is confined to areas of the South Island where cattle have contact with infected sheep, though we have had outbreaks of clinical diarrhoea in the Waikato, so we cannot rule this out.
  • Campylobacterosis is a rare disease that colonises the genital tract of cattle that can cause irregular oestrus cycles, uterine infections and early embryonic death. Bulls show no clinical signs.
  • Listeriosis causes sporadic or small clusters of abortions, usually in late pregnancy and is always associated with feeding silage that has been contaminated with soil, has low dry matter and has undergone incomplete fermentation.


  • Bovine Viral Diarrhoea (BVD) is one of the most significant causes of bovine abortion in New Zealand. BVD causes infertility, abortion, weak calves, congenital defects and can worsen the effects of other abortion agents by suppressing the immune system. The pattern of disease depends on the stage of pregnancy when infection first occurs and the previous disease exposure. Persistently Infected (PI) animals are the often the source of infection, so breeding bulls should always be tested for BVD as well as vaccinated.


  • Neosporosis is one of the most common diagnosed causes of abortion worldwide. Cattle become infected by consuming food and water contaminated with Neospora in dog faeces. Dogs become infected by eating aborted material or infected cow meat. There is also significant transmission from mother to calf in the uterus, and these heifer calves are at greater risk of aborting to their first pregnancy. These congenitally infected heifers will be permanently infected for the rest of their life and are at a higher risk of aborting at each pregnancy. Abortion can occur at any stage but is most common at five to six months. Neospora is also associated with stillborn and weak calves. Many herds will be endemically infected and suffer chronic higher abortion rates than normal, though storms can occur if the herd is naïve or immuno-suppressed.


  • Aspergillus is associated with feeding of mouldy hay or silage. Fungal abortions usually occur in late pregnancy. The incubation period varies from several weeks to several months and requires exposure to large amounts of contaminated feed. There are no other clinical signs in cows that abort to aspergillus.
  • Mortierella is similar to Aspergillus except cows that abort due to Mortierella go on to develop a fatal mycotic Pneumonia, as the fungal infection spreads from the uterus to the lungs.

Diagnosis of fetal loss can be tricky due to the sporadic nature of the organisms and as we have so many non-infectious causes. We need a thorough herd history and a range of samples from maternal blood to placenta and fetus. A freshly aborted fetus will often give us the best chance of diagnosing what caused its death.

If you are concerned about a higher than expected empty rate, see aborted fetuses or have a significantly different scanning o calving rate, give your local Anexa FVC clinic a call.

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