Worms: Assessing the Problem
A Hidden Problem
Like an iceberg, the worm problem is largely hidden. It's what you can't see that's going to cause the most serious damage and the greatest potential losses. According to a [recent study from Iowa State] sub-clinical disease caused by parasite infection that goes undetected can cost $190 per animal.
Suppress Appetite, Reduce Daily Gain
Reduced feed intake is the largest single effect of parasites on production. Heavy internal parasite infestations can limit intake of feeds and forages by cattle. The limiting or depression of intake subsequently depresses the intake of nutrients including protein, energy, minerals and vitamins. All are critical to cattle health and well being. In the dairy cow, energy intake is critical to milk production. During periods of internal parasite infestation when intake is depressed, energy intake is also depressed, all reducing milk production.
Parasites Directly Affect Immune Response
The damage done by internal parasites to the gastrointestinal tract can greatly depress absorption of a variety of nutrients. Another critical aspect of cattle performance affected by parasitized cattle is health. Research shows parasitized cattle can't effectively respond to vaccination programs (connect to the following whitepaper Gasbarre, Louis C., The Interaction of the Bovine Immune System and GI Nematodes presentation, Intervet Cattle Veterinary Meeting, Denver, Colo., June 2006.) It takes a minimum of two to three weeks from removal of parasites for cattle immune systems to effectively respond to a modified live vaccine. As an animal attempts to develop immunity against the internal parasites the animals ability to respond to vaccines is impaired or reduced. This results in greater susceptibility to infection and a reduced ability of the animal's immune system to fight off pathogens. The picture below shows changes in the size of draining lymph nodes after infection with Ostertagia.
Changes in size of draining lymph nodes after infection with Ostertagia
When a cow freshens, stress on her immune system increases dramatically. As this image of lymph nodes illustrates, a parasite burden hinders the cow's ability to fight off disease-causing pathogens. In fact, research shows that parasitized dairy cattle can't effectively respond to vaccination programs.