What fecal egg counts can tell you about your herd's parasite control program.
When producers call Bert Stromberg for recommendations on parasite control products, the University of Minnesota professor of parasitology counters with a question of his own. "How do you know you need a parasite control program?" he asks.
Stromberg admits that the odds are certainly in favor of a parasite problem existing in most herds. But like virtually anything else in the beef business, being able to measure either the problem and/or your progress provides the best use of resources.
"I've worked with cow-calf herds where we've basically found no parasites," Stromberg says. "I have a hard time recommending anyone go out and spend a lot of money on any anthelmintic without knowing if they need it."
The Eggs Per Gram (EPG) Test There are a handful of methods for doing such an assessment, but the most widely used, due to its simplicity, practicality and low cost, is an EPG (eggs per gram) of feces. A laboratory procedure, the EPG is a method to measure the number or the concentration of parasite eggs in a fecal sample. If viable samples of a representational cross-section of the herd are submitted, an EPG assessment can provide both a general determination of the numbers of gastrointestinal parasites the individual animals are carrying, as well as the potential for parasite transmission in the herd.
While it is the most practical, the EPG is not the perfect test, says Louis Gasbarre, an Agricultural Research Service parasitologist at Beltsville, MD. "But it can be very valuable in decisions concerning animal and pasture management and when to administer anthelmintic treatment," he says.
One problem with the EPG, Gasbarre says, is that it can't accurately measure incidence of the most economically damaging gastrointestinal nematode - Ostertagia ostertagi. Ostertagia is a member of the "strongyle" class of nematodes. The eggs of strongyles are so similar that they're difficult to tell apart under microscopic examination. Other strongyles include Cooperia, Haemonchus and Trichostrongylus.
Minnesota's Stromberg says that while that factor prevents an exact count of Ostertagia in a fecal sample, it's not a huge problem since all anthelmintics are effective against all strongyle-type larvae.
Proper Sampling Is Critical Two bigger concerns, he says, are making sure the samples submitted are taken and submitted correctly, and that they constitute a representative cross-section of the herd. These factors are musts if a producer is to receive the most benefit from the EPG procedure.
To effectively use the EPG procedure, individually-identified samples from 15-20 animals in the herd should be submitted, Gasbarre says.
"Most animals in a herd will have relatively low EPG values, and a few will have relatively high values," Gasbarre says. "As a result, a small percentage of cattle is responsible for most of the parasite eggs passed on to pastures."
Therefore, for the most accurate EPG result, Gasbarre says it's important to ensure that at least one or two of these high EPG individuals are included in the sampling. That's the reason for the 20-animal threshold. It's also important, he adds, to make sure the selected animals cut across all factors, such as age and sex.
Age is a factor, Gasbarre says, because of the development of at least partial immunity as cattle grow older. "Calves have the highest mean EPG values, followed by yearling cattle. Mature animals show the lowest EPG values. And in general, male cattle have higher EPG values than females," he says.
Timing Is Important Gasbarre recommends that sampling be done within particular age groups - 15-20 heifers, for instance; or the same number of mature cows or calves. He also recommends collecting samples at the same time of the year and from the same pastures, using the same selection criteria for sampled animals each time. This, he says, will help a producer determine if parasite transmission is higher or lower than previous years.
Regarding timing of the sampling, Stromberg suggests just before or immediately after spring turnout if you want to determine if your herd has a parasite problem. For calves or younger animals, fall is best.
"Timing, however, is very dependent on geography," Stromberg adds. "In the North, the ideal sampling time after turnout is May. As you go farther south it gets progressively earlier. For producers in the Deep South, who essentially have year-round calving, I'd suggest sampling at calving time," Stromberg says.
Gasbarre recommends a prophylactic approach to deworming and using an EPG test in the summer to determine the deworming program's effectiveness.
"The early season treatment would keep numbers from building up in animals and on pastures. Then in summer, I'd sample my young animals because they'd be the most sensitive to the larvae buildup. If you get a fairly high number of parasites, then your strategic program didn't work well and you need to get in there," Gasbarre says.
Where To Go, How To Do It Most any veterinarian and a number of educational institutions can conduct the EPG analysis. A few anthelmintic companies offer the EPG assessment as a customer service or marketing feature. The cost of an EPG assessment at the University of Minnesota, for instance, is $5 per sample. Actual sampling can be done by either a producer or a veterinarian. Gary Averbeck, University of Minnesota parasitology lab technician, says samples can be taken directly from the rectum and packaged in the plastic obstetrical glove used to get the sample. Or, fresh samples can be taken off the ground and placed in a sealed plastic bag or a plastic Dixie-style cup with a cover.
"The important thing about sampling is making sure it's fresh and you can identify it to a particular animal," Stromberg says. "Actually, it's not so important to identify the individual animal as the class. That way, you know you have a good cross-section of your herd and the results will be much more valid."
Averbeck cautions about "pooling" fecal samples from a number of animals and submitting just one sample. "It's a way to save money because you're only paying for one test, but it really limits the reliability and usability of the results," he says.
Once the sample is taken, it can exist for 3-4 days at room temperature without compromising the sample too much, Averbeck says. But for the best results, the fresher the better, he adds. "Ideally, refrigerated samples overnighted to the lab are best."
There are two EPG methods. One uses flotation to bring eggs to the surface of the test tube. The other uses a centrifuge to isolate the eggs. The end result is placed on a slide and microscopically examined to count the parasite eggs present.
The report will list the various parasites and their concentration. Besides the strongyles, other species identified would include Nematodirus, Trichuris, Strongyloides, tapeworms, flukes and coccidia. All are recorded as the number of eggs per gram of fecal material.
The Threshold For Treatment Stromberg considers two eggs of strongyles per gram of fecal material in a mature animal as the threshold level for recommending a parasite control program. "We used to say anything 20 and below was questionable for treatment. But now, I believe that with much above two eggs, you end up with a lot of contamination," he says.
Stromberg's calculations indicate that a cow at two eggs per gram will produce a total of almost 5 million eggs over the grazing season. "A lot of the eggs will never develop and become infective larvae, but it gives you an idea as to what the contamination level can be," Stromberg says.
Gasbarre, meanwhile, is more conservative on the threshold level. "If you intensively sample a particular age group, and that group is on generally good forage, I'd treat mature cows that test at 10 EPG and above, calves at 100 EPG and above, and heifers at 50 EPG and above," Gasbarre says. "And that threshold isn't an average for the group. If any members of an intensively-sampled age or gender group have more than those minimums, I'd treat the entire group."