Assessing the risk of parasites
Understanding parasites, and the impact they will have on your cattle, is the first essential step to assessing the risk they present, and determining how best to manage them on your farm. Understanding when they will infect cattle under typical farming conditions is also important. Cattle are frequently infected by several parasite species simultaneously. The makeup of infections i.e. which species are present, influences the impact on health and productivity and how to best control them. Planning an integrated approach to the parasite threat allows for targeted strategies to be developed, which include appropriate treatments. Well-designed parasite control programs prevent outbreaks and slow the potential development of drug resistance.
Seasonality impacts parasite effects
Seasonality will inevitably impact plant growth, pasture management, cattle husbandry, farm management, housing, and parasite challenge. Once cattle start to graze, they quickly acquire new infections from pastures with populations of infectious parasite larvae. Parasite exposure typically begins when cattle are moved to spring pastures and increases up to mid-summer.
Farm to farm variation of parasites
Infections with the lungworm Dictyocaulus viviparus are more common from July onward. There is, however, significant year-to-year, farm-to-farm and pasture-to-pasture variation, so work together with your local veterinarian to understand your specific requirements for parasite control.
Gutworm
The two most common species associated with parasitic gastroenteritis (PGE) are Ostertagia ostertagi and Cooperia oncophora. Ostertagia is the more pathogenic of the two species so is more likely to cause clinical disease. The subclinical losses from species such as Cooperia (and several other minor species that are often implicated in mixed infections) can, however, be highly significant. Cooperia species commonly infect young cattle in their first grazing season. With age and exposure, cattle develop immunity to some species of worms. Once developed, immunity can help protect against clinical disease, but even immune cattle will carry a worm burden. Though they may not show obvious clinical signs, a subclinical infection can cause substantial production loss.
Co-infection with Ostertagia and Cooperia can potentially cause a larger reduction in growth rates in calves than either species does individually, so it is important to address both in control programmes. Although their lifecycles and epidemiology are broadly similar, their sensitivity to commonly used anthelmintics does vary. Attention must be paid to the respective product labels regarding efficacy profiles, particularly the effectiveness on specific species, worm stages, and duration of activity.
Other parasite species that make up the parasitic gastroenteritis complex infecting cattle include Haemonchus. Unlike Ostertagia and Cooperia it is a blood feeder. The adult parasites have a piercing lancet at their head that is used to cut into the mucosal lining in the abomasum, enabling them to suck blood. Blood loss from heavy Haemonchus worm burdens leads to anaemia, weakness, protein loss and sometimes death.
Lungworm
The cattle lungworm Dictyocaulus is as significant cause of respiratory disease in cattle and affected animals have an increased susceptibility to infective pneumonia. It is most commonly seen in calves and heifers on dairy farms, but is increasingly common in older dairy cows and the disease can also be found in beef calves.
Lungworm can be controlled by vaccination before turnout, or through strategic use of anthelmintics at, or following turnout. Vigilance is important later in the grazing season after the persistent effects of the product used have ended, or vaccine induced immunity has begun to wane. Alternatively, a targeted approach can be adopted throughout the grazing period with cattle closely monitored and treated if lungworm infection is identified. If calves are not vaccinated or treated with a long-acting de-wormer before turnout they will need to be monitored throughout the grazing season for signs of disease.
At the start of each grazing season, youngstock may have very limited immunity to Dictyocaulus and will be vulnerable to infection. Be alert to potential Dictyocaulus exposure and take steps to reduce or prevent it if possible. High stocking rates, warm wet weather, and poor worm control during the summer can lead to outbreaks of disease later in the grazing season.
Quarantine to minimise impact of worm
Quarantine treatment for cattle imported from outside the farm will also help minimise the risk of importing novel and unwanted infectious agents, including parasites that were not previously present on the farm, or resistant strains of parasites.
Diagnosis of parasites
Diagnostics have a role to play in helping the control process and animals need close monitoring throughout the grazing season. Individual or pooled faecal egg counts can provide an indicator of worm burdens early in the grazing season before calves develop immunity to gutworms. As the season progresses they can provide a useful tool for monitoring trends and infection dynamics.
Other diagnostic techniques include the detection of bulk tank milk antibodies using ELISA. This is a rapid and inexpensive test for assessing herd exposure to pathogens in dairy cattle herds, particularly against Ostertagia.
Monitoring weight gain in growing cattle is a powerful assessment tool. Clinical and subclinical infections of Ostertagia and Cooperia can cause weight loss, therefore under-performance may indicate a problem. Faecal egg counts are not useful for lungworm diagnosis, but the Baermann test provides a method of extracting worm larvae from faeces and can be used for the identification of Dictyocaulus larvae. Further details of these tests can be obtained from you veterinarian or animal health advisor.
Treating parasites
All the major worms of cattle can be controlled through appropriate worm management techniques. These work to minimise exposure, particularly of the most susceptible individuals, alongside correct application of appropriate treatments to alleviate the effects of existing burdens and to reduce the risk of subsequent infection.
How to get the best from your parasite product
- Choose the most appropriate product for the worms likely to be present.
- Target the right worms at the right time as this will improve results and may mean re-treatment is less likely to be needed.
- Administer products at the right dose.
- Store and handle products safely and correctly.
- Consult the label and/or datasheet before using a product.
Once the treatment of choice has been made it is important that it is administered correctly; ensuring cattle are weighed prior to treatment and dosed according to the label recommendations; using appropriate dosing equipment and checking to make sure it is calibrated correctly before use. Don’t forget to keep accurate records, including dates, especially for observing the licensed milk and meat withhold periods.
