Liver Fluke (Fasciolosis)
Cattle can carry a significant liver fluke burden, with few obvious signs of disease. However, fluke infestation in this
‘chronic’ form leads to loss of performance and body condition, poor appetite and lower feed conversion efficiency. The animals are also more likely to pick up other, more harmful infections.
Chronic infection with adult and immature fluke occurs in early autumn onwards and can be tackled by a number of products. Products
such as Triclabendazole and Closantel kill immature and adult fluke whereas others, such as Clorsulon and Albendazole, are active against the adult stages.
Combination fluke and worm products can be used at housing and again in the spring, when the majority of the fluke are adult and
susceptible to the drug. This will limit the number of fluke eggs shed on pasture at turnout.
Always consult the product label regarding meat and milk withholding times. Many products are not suitable for dairy cattle
producing milk for human consumption, unless they are used at the start of the dry period.
Gut Worm Scours (PGE)
Wormers are widely used to control the adult and larval gut roundworms that cause ‘Parasitic Gastroenteritis’ (PGE), which
usually manifests itself in late summer.
Worms are active in the pasture from early spring onwards, favouring temperatures above 10 degrees centigrade and high humidity
levels. Larval activity drops off during high summer, due to the intense sunlight and drying out of the pasture and animal faeces; resuming again with the autumn rain.
Products are grouped according to their chemical structures into three main ‘broad spectrum’ categories:-
Group 1 – The Benzimidazoles (BZ) e.g. Albendazole
Group 2 – The Imidazothiazoles & Tetrahydropyrimidines (LM) e.g. Levamisole
Group 3 – The Macrocyclic Lactones, Avermectins / Milbemycins (AV) e.g. Ivermectin
Wormers in the above groups will be active against the major species of gut worms and lung worms. Some will also be active against
tapeworms and liver fluke.
The products in group 3 - Avermectins / Milbemycins - offer varying degrees of persistent activity against gut worms. They are also
active against some external parasites and are therefore termed ‘Endectocides’.
All the licensed anthelmintic products are very effective in controlling adult and immature stages of the major gut worms that cause
PGE. Fortunately, there is currently little drug resistance amongst the cattle worm population.
The Endectocide products, in either pour-on or injectable forms, offer persistent activity and can be used at strategic times
throughout the grazing season to afford lasting protection from gut parasites. Consult the product data sheet to determine the recommended dosing interval for each product.
Long-acting injection and bolus products are also available, offering sustained control of parasites over the grazing season. These
are suitable for growing young stock, but have long withdrawal periods, so may not be suitable for finishing cattle.
The product selected for the autumn, as a housing dose, should have efficacy against Ostertagia worm larvae that have
‘arrested’ and gone into a dormant stage. Failure to control these arrested larvae can mean a sudden flush of worms, causing severe diarrhoea and loss of condition, when the larvae resume
development in the late winter and early spring period.
Parasitic Pneumonia
Most anthelmintics available on the market are highly
effective against both adult lung worms (Dictyocaulus viviparus) and developing fourth-stage larvae.
An oral vaccine is also available for the prevention of lung worm in calves.
