Ask the experts: Calves with infectious abortion

9 May 2024

Question: Can a two-year-old pregnant heifer that has never calved before test positive for infectious abortion?

Answer: If the two-year-old heifer comes from a contaminated cow, or if the cow was not contaminated but the heifer acquired infected placentas from a placenta bank as a calf, or Brucella abortus was acquired through the ingestion or licking of contaminated afterbirth, the heifer can indeed become infected with infectious abortion.

It is important to handle afterbirths carefully to combat the spread of brucellosis. Bury the afterbirth deeply and sprinkle slaked lime on it. The membranes can also be burnt, but be careful to prevent fires spreading.

An infected afterbirth can release more than 46 million Brucella abortus bacteria into the environment, enough to infect many cattle.

The following questions are important:

  • If it is a contaminated herd and calves from contaminated cows are kept separate, are they specially marked and kept separate from other calf crops?
  • Are they calved separately?
  • Are the heifers vaccinated according to instructions at four to eight months with a registered Brucella vaccine? (Design Biologix BRU-TECT Strain 19, Onderstepoort Brucella abortus Strain 19 or MSD’s RB51. All three are live vaccines, so handle them with care).

With this information as background: If the heifer is infected and more than five months pregnant, she can test positive for Brucella abortus. The bacteria reside inside the cells of lymph nodes, the uterus and the udder (and in the testes of bulls), so the immune system does not even notice them. 

To grow, the bacteria require the sugar erythritol, which is only produced at five months of pregnancy. Once the bacteria multiply and escape from the cells, the cow can produce antibodies and she can be found positive with serological (blood) tests. 

It sometimes happens that antibodies are only produced after birth. That is why it is important to retest calves and cows 30 days after calving. Infectious abortion is a complex disease, so a short answer is not always simple.

Inquiries: Dr Sewellyn Davey, sewellynd@gmail.com

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