Small Brown Stomach Worm

(Ostertagia ostertagi)

Small brown stomach worm is a major production-limiting parasite of young and young adult cattle in the temperate, winter rainfall and non-seasonal rainfall districts of Australia. The impact of this worm is increased if present in mixed infections with small intestinal worms (Cooperia species) and nodule worm (Oesophagostomum radiatum).

Small brown stomach worm are small red-brown worms, 8-12 mm in length and just visible on the lining of the fourth stomach (abomasum). Adult female worms lay 50–100 eggs per day but this is variable. Small brown stomach worms do not feed on blood but damage the lining of the fourth stomach which becomes thickened and red, and in heavy infections, covered with the whitish nodules (1–2 mm in diameter) of damaged gastric glands.

Adults can become arrested or inhibited inside the cattle for extended periods and resume activity when there is a return to favourable environmental conditions for larval survival on pasture. Modern anthelmintics active against the inhibited stages in the abomasal walls have reduced the severity of the disease but resistance to these drugs is becoming apparent.

Figure 1. Anterior end of a small brown stomach worm, Ostertagia sp. Image courtesy of Lindsay Jue Sue and Constantin Constantinoiu

Disease types

There are three types to the disease pattern in cattle:

Type 1 disease affects calves during their first infection.

The timing of infection varies by region. In southern winter rainfall regions, egg development occurs from autumn to late spring or early summer. In regions with more uniform rainfall first infection typically occurs in summer. Most of the infection, is due to development directly into the adult worm stage without inhibition, producing loss of appetite, anorexia, a profuse watery diarrhoea and rapid loss in live weight. Type 1 disease is the major worm problem of cattle in winter rainfall and other temperate climatic regions.

Pre-Type 2 disease affects yearling and adult cattle, particularly beef cattle, and consists of massive accumulations of fourth (L4) pre-adult stage larvae in the wall of the abomasum.

Infection is usually picked up in spring and early summer. Inhibited larvae tunnel into the abomasal wall for up to 6 months. Clinical symptoms of affected cattle are absent although live weight gains may be sub-optimal.

Type 2 disease occurs when the arrested larvae leave the stomach wall en masse to resume development into adult worms. Just a few larvae emerging from the abomasal wall may not cause many problems but when large numbers leave the wall at the same time, severe symptoms can develop.

Type 2 disease is typically seen in rising 2-3 year old cows in late summer and autumn especially in association with calving and nutritional stress. A consequence of infection is that the pH of the stomach rises to between 5-7 making protein digestion difficult and allowing overgrowth of bacteria leading to diarrhoea. Animals do not lose their appetite but ironically, they often die from starvation because the food ingested is not digested due to the malfunctioning abomasum. Fortunately, Type 2 disease is now rare, possibly as a result of the introduction of effective anthelmintics some decades ago.

Further ecological information on worms and their control:

• Roundworm life cycle and life stages
• Small brown stomach worms have a typical roundworm life cycle except that the fourth stage (L4) larvae can undergo an inhibited phase in the wall of abomasum (fourth stomach) in response to season of the year when the infective larvae were ingested. Infective larvae can survive in dung pats for up to 14 months and are capable of overwintering in cold regions. The pre-patent period is 21-24 days, and about 28-30 days for inhibition-prone strains.
• Climate factors contributing to paddock contamination with worms
• Pasture management to reduce exposure to worms
• Cost of roundworms

Location in cattle

The fourth stomach (abomasum).

Signs

Typically, in Type 1 disease, decreased growth rates and loss of weight due to poor nutrient absorption are present. Pre-Type 2 disease can present with some production loss in the absence of obvious signs of disease. In Type 2 disease, cattle with heavy infections rapidly lose condition, develop profuse scours and may die. Animals with fewer worms are unthrifty and daggy.

Signs of worms

Diagnosis

The only accurate way to confirm worm infections in cattle up to the age of 12 months and before productivity losses have occurred is to conduct a worm egg count. Also request a larval culture or DNA test if you suspect other pathogenic worms are present. The results allow you to determine the need for a drench or management action.

‘Diagnostic’ drenching (drenching when worm egg counts are low but there is a history of favourable conditions and suggestive clinical signs) using a fully effective drench that also kills the inhibited stages in the abomasal wall, should result in improved condition and weight gains if the cause was small brown stomach worm AND the drench was effective.

Figure 2. Cow suffering from Type 2 Ostertagiasis. Image courtesy of David Swan

Worm egg counting does not always correlate well with the number of adult worms present for cattle over 9 months of age and require interpretation by an experienced veterinarian or adviser. 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.

Figure 3. Scouring and sand from cow suffering Type 2 Ostertagiasis. Image courtesy of David Swan

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.

Damage and inflammation of the gut resulting in lesions on the wall of the fourth stomach (abomasum) produce a ‘Morocco’ leather appearance at post mortem examination.

Figure 4. Nodules in the fourth stomach of a sheep caused by small brown stomach worm. Image courtesy of Dr R Woodgate, Department of Agriculture Western Australia

Treatment

There are many options to treat for this worm and your choice of drench and management options will depend on:

• The current size of the burden of this worm.
• What other worms are also present and in what proportion?
• Which drenches are effective on your property and the length of protection you are seeking?
• The likely worm-risk over the next few months.
• The likely level of worm contamination on your pastures.
• The class of stock affected and their susceptibility to worms.
• The last drench group/s you used on this (and other) groups of cattle.
• The time until these cattle are sold/slaughtered and the withholding period and export slaughter interval of drenches you might use.
• If these cattle are producing milk for human consumption.

Your decision can be assisted by using the how to decide which animals to treat section and choosing and using products. 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 Paraboss integrated Annual Programs for Cattle that have been specifically developed for different regions across Australia.