Post-weaning diarrhoea (PWD)

Russ Tyler
Formerly Queensland Government

Post-weaning diarrhoea (PWD) is a very common condition in weaned calves. It is mainly caused by two coccidia (Eimeria bovis and E. zuernii) that normally inhabit the intestinal tract. Cattle contract these organisms from herd mates within a day of birth.

Under normal circumstances, coccidia cause no significant problems as cattle develop an immunity that keeps the coccidia populations suppressed. However, if the immune system in the calf’s gut is compromised, the parasite can reproduce rapidly and cause substantial damage to the intestinal lining. This is expressed as bloody or black diarrhoea.

Weaning is a very stressful time for a calf and this stress can compromise the immune system, allowing these coccidia to build up. The immune system in the intestinal lining requires a constant flow of digesta. Interrupting the feed supply to weaned calves for as little as one day can compromise the gut’s immune system and precipitate coccidiosis. Usually clinical disease will become apparent about four weeks after the time when the immune system was suppressed.

The parasite usually damages its own environment to the extent that it no longer has a suitable environment in which to successfully reproduce. At this point intestinal populations of coccidia decline rapidly and the disease regresses. In other words; the disease is typically self-limiting, but unfortunately not before damage has been done.

If an affected calf is not given drugs to control the parasite, it may continue to suffer chronic intestinal damage from coccidia. If left untreated, the intestine can be scarred, which may affect long-term growth.

These strategies for managing PWD are recommended:

  • Ensure calves have access to nutritious palatable feedstuffs to satisfy voluntary feed intake from the point of weaning. This can be done by putting good quality hay in the weaning yard on the day the calf is weaned.
  • Reduce the stress of weaning as much as possible. Give calves access to warm dry yards with shade and a plentiful supply of clean water.
  • Include a coccidiostat in the calves’ rations. Rumensin® (active ingredient monensin) is a commercially available product commonly used in calf rations. It should be included to achieve an intake of approximately 25mg/head/day. Rumensin may also help control an outbreak of PWD. Take care in using this product: over-dosing in cattle is quite toxic, and in horses even small amounts can be lethal.
  • In calves that suffer severe and or chronic PWD, treat individually with Scourban® (which cattle vets can prescribe), a product that includes a coccidostat, an antibiotic and anti-diarrhoeal powders.

For more information see Calf rearing, Weaning and Weaner supplements.