Parasites

Internal parasites (endoparasites )of cattle affect the gut, lungs and liver. Roundworms affect the abomasum (4th stomach), intestine, lungs and liver. Tapeworms parasitise the intestines. Flukes parasitise the liver and rumen.

 They have a fascinating variety of lifecycles. All have immature and mature stages; where the immature stage involves another species that species is called the intermediate host. The sexually mature parasites living in the primary host lay eggs, which must go through a lifecycle development before reinfecting the primary host in the next generation

Host animals may be infected with internal parasites by:

• Directly ingesting infected larvae, typically off pasture, eg Ostertagia worm larvae and liver fluke.
• Ingesting the intermediate host, such as the oribatid mite harbouring a tapeworm intermediate.
• Penetration of the host, eg skin penetration by hookworm and threadworm.
• Maternal transmission eg hookworm travelling across the placenta or in the colostrum.

Endoparasites are normally diagnosed by faecal egg counts. Laboratory examination can determine not only the type of infection present but can also determine the concentration of eggs which provides information about the number of worms a cow is infested with

Gastrointestinal parasites (roundworms)

Gastrointestinal parasites are typically a problem of youngstock. While calves are drinking milk or suckling their mothers (beef) they are relatively safe from most worms. However from weaning until about 15 months old they are vulnerable.

Worms may absorb nutrients from the host’s food within the gut. They can destroy mucosal gut cells, resulting in inflammation, secondary bacterial infection and ulceration. They can suck blood, physically obstruct the gut lumen and damage other organs as they migrate through the body. Sometimes they may activate the immune system causing hypersensitivity of the gut.

The main roundworm culprits, Ostertagia, Trichostrongylus and Cooperia are widespread in cattle areas in Australasia, particularly where there is reasonable rainfall and grass growth. Mature worms live in the cow’s gut and lay 1000s of eggs. These eggs then hatch on pasture and develop into an infectious, free living larval stage, whichcan be  re ingested to restart the cycle.

Pasture larval loads peak during warm and wet periods, notably autumn and spring. When infected larvae are ingested, they multiply and grow in the abomasum (4th stomach) and intestine, doing damage and laying more eggs.

Seasonal infectious peaks appear in the autumn, but outbreaks can appear where larval development is arrested over winter and a high load of infected larvae mature at the same time (ostertagiasis type II).

When it comes to controlling worms, there is no substitute for a good oral drenching program. Good drench programs attempt to not only keep the animals (calves) from building up huge worm burdens; they also help create clean pasture for the animals to go on to.

Adult cows generally carry very light worm burdens and shed few eggs. However during the periparturient period they may be more vulnerable, as their immunity wanes and pasture contamination may rise. A number of studies with new anthelminitics suggest there is an economic advantage to worming dry cows,

particularly close to calving.

Treatment and Prevention

Untreated, or treated incorrectly, worms can be a major health and production issue on farm. Parasitism can be fatal, or can lead to long term growth reduction and under performance. Larval levels can build up on pastures, creating huge challenges in certain situations, and drench resistance may develop, increasing the toll worms take on the system.

A successful drench program requires planning. There is a large array of possible drench products, and simply paying for the most expensive one will not fix the problem.

 Major drench families may be rotated, or combination drenches employed. Egg count reduction tests should be done occasionally, to monitor for resistance, and egg count monitoring should be done as a follow up.

Most dairy calf drenching programs are built around approximately 6 treatments at 4-6 week intervals from 4 months of age. Generally, the drenched stock should be shifted to fresh uncontaminated pasture. This can be generated by harvesting, cropping, grazing by mature animals or grazing by another species. 

As the incidence of drench resistance increases there is more and more science recommending we manage the population of worm larvae to allow non resistant worms to compete with resistant ones. Some of these management practices appear contrary to best practice but may be worth looking at. If you are an organic farm we also might need to look closely at sustainable control options.

There are many options to consider with a drenching program. Make sure you see us before deciding on what to do, as it is too easy to choose a plan or a product which wastes money and is ineffective. 

Lungworm

Lungworm infections are only significant in young cattle under about 10 months of age. Infective Dictyocaulus larvae are picked up off the pasture, and swallowed. They penetrate the gut but then travel to the lungs, where they grow to adulthood. Adult worms lay eggs in the lungs, which are coughed up, hatch and are passed out in the faeces so the cycle continues...

Infection results in a productive “foreign body” cough, which is unresponsive to antibiotics. Severe infections can lead to breathing difficulty and even death. Treatment with antibiotics and antiinflammatories such as Metacam can support the recommended de worming anthelmintics.

Regular worm treatments for gastrointestinal worms normally cover lungworm, hence lungworm disease is only seen rarely, in situations where pasture contamination is high.