Sioned Timothy, ruminant technical manager at Boehringer Ingelheim Animal Health, advises cattle producers to take an evidence-based approach to parasite control.
Parasites such as worms and fluke are a significant cause of production loss in cattle, affecting growth and milk yield and, in some cases, causing clinical disease.
Parasite infection levels can be reduced by the use of anthelmintics, which in turn reduces the impact on cattle production and profitability.
However, it is important to understand how to use parasite treatments sustainably to optimise their effectiveness without selecting for resistance.
Ms Timothy says: “The differences in parasite populations and on-farm management varies at individual farm level, so control plans need to be tailored on a farm-by-farm basis.
“Cattle producers should work together with their animal health adviser or vet to adopt evidence-based parasite control strategies.
This brings together knowledge of individual farm history, herd performance monitoring, assessment of at-risk animals and diagnostic testing to help inform treatment decisions and measure effectiveness.
“Profitable cattle production relies on the continued availability and effectiveness of anthelmintics, so it is vital we follow best practice.”
Know your worms The aim of parasite control programmes should be to break parasite lifecycles to reduce infection in animals and their presence in the environment.
In all cases, when using anthelmintic treatments, follow the five Rs*:
Source: COWS (2018) The COWS Guide to the effective use of cattle wormers [online]
This can only be achieved if you know which parasites are present on-farm.
The most common worms encountered in cattle are the gastrointestinal roundworms, Ostertagia ostertagi and Cooperia spp, which together cause parasitic gastroenteritis.
Infection with Ostertagia is more likely to result in clinical disease, with symptoms such as weight loss, scouring, reduced milk yield and longer calving to conception times.
The impact of this worm is often more severe in youngstock, so they should be a focus in control programmes to ensure large worm burdens do not build-up.
Cooperia is less likely to cause disease, but it can cause weight loss when burdens are high.
Cattle are frequently co-infected with Cooperia and Ostertagia, but the susceptibility of these parasites to anthelmintics may vary, so advice is needed on the most appropriate wormer for these species.
The bovine lungworm Dictyocaulus viviparus is a real threat to calves, and clinical cases are increasingly being seen in adult cattle.
This worm can cause serious respiratory disease, resulting in significant production loss.
Outbreaks are more likely in late summer and autumn, but can be unpredictable, with the risk of infection increasing after hot dry weather followed by rain, as larvae are released in high numbers from dung pats.
Fasciola hepatica (liver fluke) is a very important cause of production loss in cattle, leading to reduced milk yield, poor growth and lowered fertility.
Rumen fluke (Calicophoron daubneyi) thrives in the same conditions as liver fluke, however its impact on cattle is unclear.
Of the two flukes, Fasciola hepatica is the more serious threat.
Your vet can identify which species of parasites are present on-farm and, in cattle, by using a variety of diagnostic tests.
Not all wormers treat the same parasites, and the spectrum and efficacy of different anthelmintic compounds against key parasites varies.
Using an inappropriate product is inefficient, costly and risks increasing the likelihood for anthelmintic resistance.
Your vet or animal health adviser will take all these factors into consideration when recommending an anthelmintic treatment.
The group of compounds known as macrocyclic lactones (abamectin, doramectin, eprinomectin, ivermectin, and moxidectin) are typically the wormers of choice for the treatment of roundworms at housing.
Products from other wormer groups are less effective against the encysted stages of Ostertagia, which can be a cause of significant disease in calves in winter/early spring.
Macrocyclic lactones have activity against common external parasites, such as mites and lice, which may pose a problem in housed cattle.
Due to the persistence of this class of wormers, one treatment a short time before or at the point of housing is normally sufficient for cattle until the next grazing season.
Treatments for the liver fluke Fasciola hepatica may be required in autumn and winter.
To immediately address the productivity impact of a mature fluke burden, it is recommended that a treatment for fluke is administered as soon as cattle are housed.
After infection, fluke go through three developmental stages: early immature; late immature; and adult.
Each of the available flukicides is active against a defined spectrum of stages.
Grazing management practices have a significant influence on the exposure of cattle to gutworm larvae.
This is particularly important to take into account in the case of youngstock as they are more susceptible to developing heavy gutworm burdens and associated clinical disease.
Before giving housing treatments, consider the pastures used and the likely exposure over the past grazing season.
This will help identify which cattle are likely to have a parasite burden and inform treatment decisions.
Individual weight gains can also provide an indication of whether animals are facing a high parasite challenge and would benefit from targeted treatment.
Once you know what parasites are present on-farm, and which cattle are likely to be carrying a parasite burden, housing treatment options can be discussed with your animal health adviser or vet.
Diagnostic testing may also be useful to determine the specific farmlevel threats.
Flukicides containing clorsulon will remove the adult stages of fluke in cattle, while those containing closantel or nitroxynil are effective against both late immature and adult stages and triclabendazole is effective against all three stages.
The choice of treatment for liver fluke at housing should take this into account, but practical considerations, such as route of administration and meat withhold times, will often also play a role.
The choice of treatment for liver fluke at housing is also complicated by emerging resistance to triclabendazole.
This is the only flukicide which treats the early immature stage of liver fluke, which causes acute disease in sheep, but does not cause disease in cattle.
Selecting an alternative to triclabendazole for cattle at housing will reduce selection for resistance and, by targeting the later stages of the parasite, control the impact of liver fluke on productivity.
To ensure cattle have no residual fluke burden, they may need to be retreated at an appropriate interval after the initial housing dose; diagnostic testing will help determine whether this is the case.
This will ensure cattle are turned out fluke-free and do not contribute to pasture contamination with fluke eggs next year.
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