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.
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.
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.
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.
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.
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.
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.
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.
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.