Black scour worm

(Trichostrongylus species)

Intestinal black scour worms Trichostrongylus colubriformis are not often seen in cattle. Sheep strains of this parasite are readily transferable to calves but the infections do not persist suggesting that this worm is not well-adapted for survival in cattle.

Dairy calves in coastal regions can become infected but in beef cattle infection only occurs sporadically. Black scour worms have been reported in low numbers in young calves in the south-west region of Western Australia. Infestations are usually part of mixed infections with the temperate small intestinal worms (Cooperia species).

All scour worms are small, hair-like worms tapered at one end. Males are 4–6 mm long and the females are 5–7 mm long, and not easily seen at post mortem. The adult female in the small intestine typically lays 100–200 eggs per day that are passed out in the dung.

Further ecological information on worms and their control:

  • Roundworm life cycle and life stages
  • The life cycle follows the typical roundworm life cycle. Larvae are abundant throughout the winter to early summer but scarce during mid-summer and autumn. Egg laying commences at about 15-20 days after infection.
  • Climate factors contributing to paddock contamination with worms
  • Pasture management to reduce exposure to worms
  • Cost of roundworms

Figure 1. Black scour worm. Image courtesy of Nick Sangster

Location in cattle

Small intestine (first 3 metres).


The small numbers usually present are harmless.

Signs of worms


The only accurate way to confirm worm infections before productivity losses have occurred is to conduct a worm egg count (WEC). Also request a larval culture or DNA test if you suspect a mixed infestation with small brown stomach worm (Ostertagia ostertagi). The results allow you to determine the need for a drench or management action.

Figure 2. (Left) Normal surface of the small intestine (Right) The wall of the small intestine damaged by black scour worm. Image courtesy of Ian Beveridge

If visual signs of worms are present in cattle then significant production loss has already occurred. Also, these signs can occur with other parasites and diseases.

Worm egg counting does not always correlate well with the number of adult worms present for cattle over 9 months of age. For this age group observation of physical signs such as body condition scoring and monitoring target growth weights are good additional indicators to diagnose worm infections.


Your decision can be assisted by using the how to decide which animals to treat section and the WormBoss cattle products search guide for your region, a simple tool that considers some of the points above. It is also important to consider cattle management options, as simply removing the affected mob to a less wormy pasture will reduce the re-infection risk.

You can also review the chemical pages on this site to find out specific information about drenches, including their drench active, drench group, how they are administered, which worms they treat, resistance status, safety information and how they work.

The negative impact of this worm can also be reduced through using one of the integrated annual worm control programs that have been specifically developed for different regions across Australia.