Shining a light on lungworm

On November 10, 2023, I was called to examine a mob of weaner calves that had developed signs of respiratory disease. The farm was a fulltime calf rearing operation, just a short drive from Feilding in the Manawatu. The farm buys four-day-old dairy-beef calves from local dairy farms and rears them to 100kg before on-selling.

They batch-rear in both spring and autumn calving seasons, with well over 200 calves having been reared in spring of 2023. At the time of the visit 100 calves were left on the property, and one mob of 30 head were reported to be affected.

All calves on the property had been weaned off milk replacer a week before our visit. The calves were being offered 1kg of pellets per head and eating the pellets well. Their weights ranged from ~80kg to 100kg, and they were in good body condition. They were vaccinated and had not yet been drenched.

The affected mob had had one calf die earlier in the week, and another was very sick and had been on antibiotic treatment for the previous four days, with marginal improvement. Walking through the paddock it was clear a large proportion of the mob were displaying signs of increased breathing effort. The mob were yarded for closer examination and drafted based on the degree of breathing effort.

Adult Lungworm, measure up to 4cm long, visible within the airways.

Fifteen animals were showing moderate to severe respiratory distress, while 15 showed mild to no signs of distress.

The remaining calves were checked and all mobs contained a small number of calves which were also showing signs of severe respiratory disease. In total 30 calves were initially treated for moderate to severe pneumonia, along with the 15 treated for a lower level of disease.

The severely affected calves were treated with a course of potent long-acting antibiotics, while the mildly affected animals received a course of cheaper, shorter-acting antibiotics. All the calves received a dose of anti-inflammatory and were also drenched with a combination containing Levamisole and Oxfendazole.

Faecal samples collected from a number of animals in the mob were examined later that day and showed very low faecal worm egg counts. Using the Baermann technique, which is a simple overnight process to test for Lungworm, we found the calves were carrying a heavy Lungworm burden. So why did this farm end up in this situation?

Lungworm is an underestimated and often forgotten parasite in New Zealand, and yet some of the worst outbreaks of worm-related disease I have seen in my 15-year career have been caused by this worm.

Weaner calves are the most likely class of cattle to show signs of disease, as heavy environmental burdens often coincide with weaning. The level of challenge from the environment, in addition to the level of physiological stress an animal is experiencing, will dictate whether the calf or parasite wins in the battle for health. Calves will readily develop immunity against Lungworm if the level of exposure is not too high. Physiological stress, such as experienced at weaning time, lowers the response of the immune system, leaving the calf vulnerable when parasite challenges are high. Drenching readily controls Lungworm in calves, however, there are two big catches:

1. Calves routinely drenched every month, and therefore never have exposure to Lungworm, become vulnerable to disease as adult cattle as they have never had the chance to develop an immune response to the worm.

Outbreaks of Lungworm-induced pneumonia and death in twoyear- old heifers and freshly calved cows have been reported on a number of occasions.

2. In calves with heavy burdens of Lungworm, drenching can cause symptoms to worsen for up to a week following drenching, as dead adult worms are expelled from the lungs. In this situation, support with anti-inflammatories and antibiotics can help animals to recover more readily.

The answer to Lungworm control does not lie in routine blanket drenching. Strategic drench programmes for calves should include only the occasional blanket drench of the whole mob, such as at weaning. Between times, drench only those calves not achieving growth rates above 500g/day.

Lisa Whitfield is a Production Animal Veterinarian in the Manawatu