Immunity to lungworm vital in husk control
WORM control programmes must allow cattle to develop immunity to lungworm, preventing costly outbreaks of husk in adult cattle.
That is the message of vet Graham David of the Vet Lab Agency in Shewsbury, Shropshire, following a study of 32 farms suffering husk outbreaks caused by lungworms.
The study began after increased incidence of husk in 1993, when 226 outbreaks were reported to the VLA. This was double the average reported between 1975 and 1992. Incidence continued to rise peaking at 520 cases last year.
But cases in 1993 were mostly in adult animals rather than youngstock, increasing the cost of outbreaks, making treatment expensive and reducing milk output. In some herds more than half the animals were infected, many herds suffered one death and in one herd 14% of an infected heifer group died.
"Only three of the 32 herds studied were vaccinating calves and two of these three herds had husk only in unvaccinated animals," said Mr David.
"There was also heavy athelmintic use in animal first and second grazing seasons at grass in affected herds. Some herds also treated animals in their third grazing season and as dry cows. Second season use did not happen in the past."
At the same time, vaccinations which allow immunity to develop have decreased. Only a quarter of the number of animals were vaccinated in the 1990s compared with the early 1980s, he added. There has also been more movement of animals between herds and more imports, possibly moving lungworm carriers into lungworm free herds, said Mr David.
"Husk is an unpredicatable disease but vaccination is a predicatable way of avoiding it." Vaccination costs are low at about £6 an animal compared with the cost of treating infected adults. "We will never eradicate lungworm, but can get cases back under control." *