My first disease screening results from our bulk milk test came back this week. The Elisa (antibody) bulk milk test results for Ostertagia (stomach worms) came back at 0.95, which was graded as high positive. All my results for last year were graded low positive. What does this result mean for my cows and what should I do?

Recent research has seen the development of tests that can detect antibodies in the milk to gutworm, lungworm and liver fluke. The interpretation of results from these tests needs to be understood in the context of the overall herd health and milk supply pattern. It is important to note that using the results from these tests alone will not be enough to design a parasite control plan. This should be put in place in conjunction with your local vet.

It is important to state that results of bulk milk testing for gutworm, liver fluke and lungworm simply indicate the presence of antibodies resulting from prior or current exposure to these parasites, and as antibodies remain in the animals for several months, they do not necessarily indicate active infection or disease.

As a general rule, all research evidence available suggests the status of adult cows two months after turnout can be considered to be fully immune to Ostertagia (roundworm) and immune to Cooperia and also lungworm if they encountered infection as calves at grass.

What to do? If you are worried, talk to your vet and take dung samples from a proportion of the herd. Dung samples may be used as part of a diagnostic strategy for detection of parasites in adult cows. This should include clinical examination, performance assessment (milk, condition score, if they’re scouring, etc) and other diagnostic tests.

Specifically, lungworm can be a problem in the second and subsequent grazing seasons if insufficient immunity has been induced in the first grazing season. This could occur if doses with persistent activity were used in the first grazing season.

Dosing adult cows for liver fluke should only be undertaken where there is a body of evidence, such as poor performance, scour and blood test results which indicate high numbers of white blood cells.

My February-born calves are out at grass for the last six weeks as I turned them out to grass in mid-March and I’m trying to design a dosing plan for them – what should I consider?

The right way to approach this is to take fresh dung samples from 10 to 15 calves approximately eight weeks after turnout and have them submitted to a laboratory to determine the number of worm eggs present.

Dung samples being submitted for testing should be as fresh as possible and ideally the lab should receive the samples as soon as possible (within 48 hours) after collection to ensure correct egg counts.

Labs can pool the faeces and do a single count that will give a good indication of the average number of worm eggs present in the whole group of calves.

What the vets call “tactical management” is strongly recommended nowadays. This means regular monitoring and only treating when appropriate.

Ideally, faecal egg counts and weighing should be carried out to gain a more complete picture of what is going on. If daily liveweight gain is less than 0.6kg per day and faecal egg count is over 200epg, then talk to your vet and treat as soon as you can. The new advice is rather than treating all animals, it may be advisable to treat only those calves with high faecal egg counts and low daily gain.

Once silage aftergrass is available, calves can be moved from paddocks to cleaner grazing that has not held cattle since previous year. Research in sheep has now shown that treatment with a worm dose and immediate movement to clean pasture increases the risk of dosing resistance.

Therefore it is now recommended that animals are held on the “dirty” paddocks for a period of 48 hours post-dosing prior to moving to clean paddocks. If clean grazing is not available, then a group treatment is recommended.