Parasite control in cattle

Endoparasites, those that live within the body of its host e.g. Cooperia, and ectoparasites, those that live on its host’s body surface e.g. lice, can pose a significant threat to cattle health and performance, with the presence of worms causing a reduction in appetite which leads to poor growth. Worms can be challenging on farms, so treatment plans should be reviewed each year, considering the farm’s location, disease history, the season and the age of stock. The risk of infection varies, so having better management and effective use of anthelmintics means the impact of parasites and risk of anthelmintic resistance can be limited.

SHOULD ALL CATTLE BE TREATED FOR LUNGWORM AND LIVER FLUKE?

It depends on the age of the stock, their grazing history and the parasite history of the farm. Young cattle are those most at risk from internal parasites as adult cattle acquire immunity and so should not normally need drenching for them. However, immunity to lungworm is short lived, so any age of stock can be affected, and there is also no age of immunity to liver fluke. Worming housed cattle can be a useful, low-risk option to deal with the worm population. 

ARE THE RISKS OF PARASITES LOWER IN PERIODS OF DRY WEATHER?

In dry weather, the level of infective larvae on the pasture is lower because the eggs and larvae remain dormant in the faeces and can’t migrate on to the pasture until rainfall has occurred. But when it rains, there is an increased risk of cattle being infected, due to the larvae being washed from the faeces and on to the pasture. This can be especially evident after autumn rains following a dry summer causing lush grass growth and potentially gut worm populations to increase.

WHEN SHOULD TREATMENT BE CARRIED OUT?

It is important to only drench animals when they require it. This is especially true in adult cattle as unnecessary drenching will lead to drench resistance. When deciding when to treat an animal consider the likely larval challenge, feed levels and the animals condition.  As already mentioned, young growing animals can face the biggest parasite challenge so consider a drenching programme starting after weaning. 

WHICH PRODUCT SHOULD I USE?

There’s a wide range of cattle wormer products available, so it’s important to use a product which will deal with the type of worm burden that you want to treat for. Combination products contain more than one type of active ingredient and so are useful to help delay the onset of drench resistance, but it is important these are used correctly.

HOW DO I ENSURE CATTLE ARE GETTING THE CORRECT DOSE? SHOULD I DOSE TO THE LIGHTEST OR THE HEAVIEST?

Estimating weights by eye is inaccurate, so ideally, all cattle should be weighed (using scales) individually for their live weight, helping to prevent underdosing or overdosing. The wrong dose can lead to the worming product being ineffective or creating toxicity issues. However, if a group of well-matched cattle are to be treated together, it is acceptable to weigh a sample of animals and treat according to the estimated weight for each animal.

RESISTANCE TO ANTHELMINTICS IS GROWING. HOW DO I CHECK TO ENSURE THE TREATMENT HAS WORKED?

The most effective way to check the treatment is by doing a post-dosing faecal egg count (a post-drench test). Pooled faecal samples are taken from 10 members of the herd that have been grazed together, usually one to two weeks post-treatment. Be aware that this test won’t determine if the wormer has been effective against some hibernating worms – such as those that cause type II ostertagiasis.

IF IT HASN’T WORKED SHOULD I TREAT THE ANIMALS AGAIN AND SHOULD I USE A DIFFERENT PRODUCT?

It’s advisable to treat the cattle again, first making sure that the wormer is the right one for the parasite. If you think the wormer has not been effective, your vet can advise on what further action should be taken.

FOLLOWING THE FIRST TREATMENT WILL ANY FOLLOW UP TREATMENTS BE REQUIRED? 

If an effective parasite control has been given, then no further action is needed. However, depending on the parasite control program, a follow up treatment may be needed, to limit the contamination of worm eggs on to new pasture. Young stock that have not built up any immunity to parasites will need a series of drenches. Your vet or animal health advisor will be able to advise on the best programme to follow.

COMMON MISTAKES THAT CAN RESULT IN PRODUCT FAILURE

• Under or over dosing due to inaccurate estimations of animal weight – weighing cattle can avoid this.
• Applying the product incorrectly for the weather conditions (using a pour-on in the rain); remember to follow the recommended guidelines.
• Improper storage of the product; always store correctly.
• Inadequately maintained dosing equipment. Ensure that the equipment being used is compatible with the wormer, that it is clean and measuring correctly.
• A product may fail if the wormer has passed its expiry date, so always check.
• Mixing wormers together or with another product can cause the ingredients to be inactivated; remember to use the products correctly.
• Incorrect application, such as wormer injection being given by intramuscular rather than subcutaneous routes, can cause failure. Avoid by reading the manufactures guidelines.
• Incorrect drug choice for the target worms; research the product so it’s effective against the worms you want to control.