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Virginia Cooperative Extension - Knowledge for the CommonWealth

Does "Ostertagia" (the "brown stomach worm") affect milk production?

Dairy Pipeline: June 2001

Ernest Hovingh
Extension Veterinarian,
VA-MD Regional College of Vet Medicine

There is some evidence to suggest that Ostertagia can affect milk production in lactating dairy cattle, although mature cattle tend to be more resistant to infection than youngstock. There has been some recent research which has investigated the level of antibodies in bulk tank milk. These antibodies are produced by the cows in response to the Ostertagia worms. Bulk milk was chosen since it is an easy way to examine a large number of animals at once and get an idea of the overall infection level in the herd. Two studies have evaluated this bulk milk test in eastern Canada. One of the studies found that the amount of "summer slump" a herd experienced was significantly associated with the level on antibodies in the milk, suggesting that deworming the mature cows might have had an economic benefit. The other study, while not finding an association with the amount of seasonal decline in production (the "slump") did find a significant association between the level of antibodies and the overall herd level of milk production. This was observed most strongly in herds that had at least some exposure to grass. But would this hold true in Virginia as well? Our climate can be well suited to the survival of the infective stages of the worms on pasture. A study is being carried out this summer to evaluate this test in Virginia. If you have received this questionnaire, we would appreciate your participation - even if your cows may not be 'on grass' at all during the summer. We would like to have a large range of management styles and herd sizes represented, and so your participation would be valued. Please ask your veterinarian or dairy agent about the research, or contact me (, 540-231-5234) if you have any questions. All information will be held in strictest confidence and we will inform you of the results and conclusions of the study as soon as they are available. If we get good participation we should be able to help you decide on the value of deworming your mature cows!

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