Parasite control in growing cattle at pasture

Internal parasites are one of the main threats that need to be considered for animals at grass. Researcher Orla Keane has some information and advice on Lungworm and Gut worm

For animals at grass, one of the major health threats is internal parasites. At this time of year gut worms and lungworm are the major internal parasites of concern.

Lungworm

Lungworm outbreaks are unpredictable and of significant economic importance. While immunity to lungworm develops reasonably quickly, it can be short-lived and regular exposure is required to maintain immunity. Therefore, immunity can wane when cattle are housed.  After turnout to pasture cattle should be closely monitored for signs of hoose and the group treated as soon as possible if clinical signs are evident. For farms in which hoose is a serious problem, a vaccine is available for the control of lungworm; however, the vaccination schedule should be completed before cattle are turned out. Therefore the vaccine is most suitable for use in autumn born calves or yearlings.  Alternatively, lungworm is controlled by the administration of broad-spectrum wormers.

Gut Worm

The main impact of gut worms is reduced feed intake and subsequent poor growth rates. The level of challenge will depend on a number of factors including stock type and age, weather conditions and grazing management. While young calves are fully susceptible to gut worms, yearlings should have some immunity built up. However, dairy and dairy cross yearlings generally have higher levels of immunity to gut worms than suckler yearlings. This is due to their higher exposure to these parasites as calves due to the higher proportion of their diet that came from grazed grass.  In fact, if gut worms are managed well in their first year, dairy and dairy cross yearlings should require minimal treatment for gut worms.  Suckler yearlings may be more susceptible to gut worms as their immunity does not develop sufficiently in the first year as they are generally not exposed to significant numbers of these parasites until close to weaning when their grass intake increases. Similarly, autumn born calves will be susceptible to gut worms when turned out the following spring and gut worm control in these animals is important.  Turning them out to clean pasture (i.e. pasture not grazed by young cattle in the last 6 months) will help reduce their exposure to gut worms.

Managing gut worms in cattle can follow a “strategic” approach or a “targeted” approach.  The aim of the strategic approach is to treat early in the season to prevent the build-up of parasites on pasture. However, this approach is dependent on the availability of products that are highly effective.  Anthelmintic resistance has recently been demonstrated on cattle farms in Ireland and the strategic approach should only be utilized if it is known that the anthelmintic is effective. Otherwise it may lead to the build-up of resistant worms on pasture. An alternative to the strategic approach is regular monitoring and targeted treatment. In this case cattle are treated only as required based on indicators such as average daily gain or faecal egg count. A herd health plan developed in conjunction with the veterinary surgeon can help mitigate the risk from these internal parasites.