2014-02-10   facebook twitter rss

Lungworm on the Increase

Lungworm infection can cost you up to £140 per dairy cow, mainly due to daily milk yield dropping by as much as 6 litres from the time you see the first clinical signs until the final diagnosis and treatment.

Lungworm also leads to loss of body condition, a drop in fertility seen as a longer calving interval and increased culling rate. In severe cases, animals will die.

Lungworm a threat to dairy cows

Lungworm a threat to dairy cows

The incidence of ‘coughing cows’ has increased substantially over the past decade, according to veterinary specialist Fergal Morris MVB, MBA, MRCVS.

“Coughing in cows can be due to one or a combination of many causes, including IBR, RSV, PI3, pasteurella pneumonia and fog fever, but in winter lungworm is the most common cause of coughing”, explained Fergal.

“Use of long-acting wormers in calves in their first grazing season results in excellent growth rates as worms are killed before they cause clinical signs of disease. However, there is a big difference in the epidemiology of lungworm and gut worm. Cattle will nearly always develop immunity to gut worm, but immunity to lungworm is much more unpredictable.

“Adult lungworms produce up to one million lungworm larvae leading to a much faster build up of infection on pasture. But the survival time on pasture of lungworm larvae is much shorter than for gut worm eggs,” added Fergal Morris, a veterinary adviser with MSD Animal Health.

Continuing Fergal noted that due to over-worming in the first grazing season many cattle will develop lungworm infection during the second grazing season. Farmers then continue to use long-acting wormers to treat and prevent clinical signs of lungworm. This may further inhibit lungworm immunity.

“Around 10% of cows are lungworm carriers and shed lungworm larvae on pasture. Because of reduced opportunities to develop immunity, first lactation heifers pick up these lungworm larvae off the pasture when they join the milking herd. Heifers, which then develop clinical signs of hoose.

“These ‘naïve’ heifers will then heavily contaminate the pasture with lungworm larvae so cows will then develop what is called the ‘re-infection syndrome’.

Complex
“This re-infection syndrome is the result of a complex cycle of lungworm infection in cows and heifers. There are two types of immunity to lungworm - short acting immunity to lungworm larvae that lasts six months and long acting immunity to adult lungworm that lasts two years.

“Cows pick up large numbers of larvae on pasture from infected heifers. When the adult larvae reach the lung there is a strong immune response resulting in clinical signs of hoose. However there might not be lungworm larvae in faecal samples as the immune system will have killed the adults before eggs are produced.

“If adult cows are continuously treated with long-acting wormers it may prevent the 10% of carrier cows shedding small numbers of larvae onto the pasture. This will eventually result in cows losing their immunity to lungworm.

“As cows will only have immunity to lungworm adults for two years, it is therefore necessary to top up the immunity by coming in contact with larvae in low numbers. This is one of the reasons that older cows can develop severe cases of hoose. These animals will have lungworm larvae in their faeces.”

Advice
According to Fergal Morris, the best option in spring calving herds is to continue to use long-acting wormers in the first grazing season in order to maximise growth rates in replacement heifers. In the second grazing season, heifers should get two doses of Huskvac four weeks apart with the last dose given two weeks before turnout.

“This gives cattle very solid immunity to lungworm and will lead to reduced use of anthelmintics in the second grazing season.”

MSD

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