It’s a given that we have all been glued to the weather forecasts that seem to change daily.  But another forecast beef producers should be informed about is the parasite forecast.
Dr. Craig Payne, Extension Veterinarian with the Commercial Agriculture Program at the University of Missouri, says internal parasite levels are going to depend upon the environmental conditions present each year.  “Although there are several parasites common to cattle, the one we are usually most concerned with is Ostertagia.”  
Ostertagia is considered to be the most economically significant internal parasite in beef cattle.  “Ostertagia is extremely active reproductively during the spring and fall of the year when cooler temperatures and adequate rainfall prevail,” Dr. Payne said.  These conditions are needed for the adult parasite to reproduce.  
When the parasite eggs are in their final stage of growth they are capable of infecting cattle.  In this stage they are called larvae.  “When cattle consume these larvae through grazing, they enter the abomasum and develop into an adult,” Dr. Payne said.
“During hot, dry weather such as summer or subfreezing temperatures, larvae that are in the abomasums enter a hibernation state and don’t mature into an adult until favorable environmental conditions return,” Dr. Payne said.
Although Ostertagia is the most common internal parasite in beef cattle, there are others to keep in mind.  Trichostrongylus axei (stomach hairworm) and haemonchus sp. (large stomach worm) live in the abomasum.  But there are many more that are present in the intestine. Here are a few:  Bunstomum phlebotomum (hook worm), Oesophagostomum radiatum (nodular worm) and trichuris sp. (whipworm).
When these parasites are found in cattle, dewormers are the fix.  Dr. Payne says there are two general categories of dewormers, Class I and Class II.  “Class I dewormers are effective against adult parasites and Class II are effective against adults and inhibited larvae,” Dr. Payne said.  To determine which category a dewormer falls in, producers should contact their local veterinarian or refer to the label.  
In mature cows Dr. Payne suggests the optimal time to deworm is when the majority of the parasites are in the animal and pasture contamination is low.  “In Missouri, deworming cows around the spring calving period would be the opportune time,” Dr. Payne said.  
There are three things that are accomplished by doing this:  most of the parasites are killed since they are in the animal, re-infestation of the animal is reduced and there will be fewer adults to lay eggs the next time favorable environmental conditions are present.
“Another time to consider deworming would be before cattle are moved to a “clean” pasture,” Dr. Payne said.  “This will reduce the probability of that pasture becoming contaminated.”
Dr. Payne tells producers most dewormers are going to be effective as long as they are used properly and producers understand their limitations.
Producers should contact an expert about putting together a strategic deworming program for their herd.
Dr. Payne believes the best advice producers can receive is to develop a good working relationship with their local veterinarian.  They know your program better than most and can help you design a system that will work for you and help predict the parasite forecast in your herd.


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