Reinfection Syndrome in Cows If cows that are partly immune to lungworms are exposed to a heavy larval challenge from pasture (e.g. pasture recently grazed by first grazing season animals), they may develop severe coughing and/ or milk drop as their immune system kills the migrating larvae. Such animals will not have lungworm larvae detectable in their faeces, as the immune response is effective, but causes the clinical signs.
If you are buying in dairy calves they will be at a much higher risk from gutworms. You will need to graze them on low risk pasture (see above), closely monitor their liveweight gain and check for signs of diarrhoea (see below re: lungworm) and regularly take faecal samples and get them tested for the presence of parasites and treat with anthelmintics accordingly.
Lungworms Clinical signs of lungworm infection (‘hoose’ cause by Dictyocaulus viviparus) include coughing and difficulty in breathing. Affected cattle have an increased risk of viral and bacterial pneumonia. Immunity aginst lungworm infection develops quickly but is relatively short-lasting (approx. 6 months) in the absence of further exposure to lungworm larvae on pasture. At the start of each grazing season, following housing, cattle may have very little or no immunity to lungworm and thus are susceptible to new infections again. The practice of purchasing dairy calves for beef and placing them on pasture that was grazed by calves the previous year is high-risk and should be avoided where possible. The highest challenge risk periods for animals are late summer and autumn. Photo of the stomach (abomasum) from a bovine animal with a heavy worm burden. Note how the lining is thickened- this stomach cannot work properly.
Lungworm larvae in the trachea of a cow that died of hoose (Photo: D. Toolan, Kilkenny Regional Vet. Lab.)
Liver fluke (Fasciola hepatica) This is usually not an issue at turn-out. If cattle have not been treated at housing, then treatment with a flukicide effective against adult liver fluke before turn-out will ensure that contamination of the pasture with fluke eggs is kept to a minimum.
SPRING EDITION 2016
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