Fall parasite management, however, should not be overlooked in yearly parasite management strategies. Implementing such a strategy can dramatically increase overall cattle performance and the effectiveness of spring deworming regimens.
Spring versus fall deworming
“The primary purpose of fall deworming is that you don’t want to feed internal parasites all winter long via harvested forages and supplemental feed,” Chris Reinhardt, professor of animal science and feedlot extension specialist with Kansas State University, says.
“The primary reason for spring deworming is to turn out non-parasitized cattle onto pasture to improve conversion of grass nutrients to productive purposes.”
Tom Yazwinski, professor in animal science with an emphasis on parasitology at the University of Arkansas, also notes that there are many differences between fall and spring deworming as well.
“Spring infections lead to pasture contamination that ‘fuels’ new infections for the remainder of the grazing season,” Yazwinski says.
“Good control in the spring goes a long way to lessening parasitisms for the rest of the year. Worms need spring and fall conditions to boost their numbers on pasture, so treatment for worms in the spring and fall is indicated for worm control in the animals and on their pastures.”
Internal parasites excrete eggs through the animal hosts’ feces. The eggs will lay dormant during colder months, particularly in the North, but hatching requires what Reinhardt calls “the same conditions for growing green grass.” The eggs wait until there is warm and moist weather to hatch, then larvae latch onto green grass and are ingested by the grazing animal.
“If we turn clean, non-parasitized cattle out onto previously infected pastures,” Reinhardt says, “we know there are eggs out there waiting to hatch, waiting for sunshine and moisture to hatch and release the infective larvae.”
By late summer and fall, the only new infective larvae in pasture is from the eggs that have been shed throughout summer grazing and, thus, without treatment, cattle will keep re-infecting their own pastures.
“We can dramatically cut down the shedding during the grazing season by turning out clean cattle onto infested pasture and then deworming again before the pasture can become re-infested with eggs from adults and larvae which were consumed in the spring after cows were first turned out,” Reinhardt advises.
Reinhardt also notes, however, that it is nearly impossible to completely eliminate egg shedding throughout the summer, so there is a need for parasite control in the later parts of the year.
Regional differences in parasites
Generally speaking, parasites that affect beef cattle are the same regardless of location.
“There’s no difference in the actual parasites,” Reinhardt says. “Cattle are susceptible to certain species and genera of parasites, but those parasites are present pretty much year-round at varying levels, and cattle are susceptible to infection by them year-round, to varying extents, depending on geography.”
Yazwinski notes that roundworms (nematodes) “are basically on all pastures and in every grazing animal, save for a few minor exceptions. You can draw a line up and down the U.S. at about Oklahoma, and everything to the west is “maybe wormy,” and everything to the east is “probably wormy.”
Using the same geographical line, Yazwinski adds that east of that line sees an increased summer inhabitation of brown stomach worms in the South, and an increased summer inhabitation in the North. In the Southeast, there is a strong barberpole stomach worm population that is relatively confined to that region.
Other widespread internal parasites such as fluke worms, various intestinal worms (i.e., nodular worms), hookworms and tapeworms are not regionally specific and impact operations nationwide.
There is some climate variation associated with the prevalence of the aforementioned internal parasites, such is often the case with fluke worms. Fluke worms are more prevalent in pastures that, at one time, were in standing water such as low-lying valleys or areas that are prone to temporary runoff.
While there may be geographical pockets of where “fluke land” usually is, such as the northwestern, Gulf Coast, and Great Lakes states, Yazwinski notes, fluke worms are more dependent on environmental conditions.
Operation types and parasite management
Fall parasite management does have some regional considerations, Reinhardt notes. For example, if you are grazing green forage all winter long, like you might in the deep South, fall deworming strategies are effective when mimicking similar management strategies as in the spring.
However, as Reinhardt advises, if you are feeding harvested forages in confinement during some or all of the winter months, fall deworming should be targeted at reducing the parasite loads internally so as to ensure the nutritional value of the feed your cattle are consuming isn’t shared with internal parasites.
Fall-calving operations also have alternative parasite management considerations than those who calve in the spring.
“If we have fall-calving cows that are going out onto lush green forage in the South, producers may need to consider a second deworming two months later during winter,” Reinhardt says. “If we have fall-calving cows in the Northern states and cows and calves are not grazing green growing forage, that cow and calf should be relatively if not completely parasite-free all winter long.”
Feedlot and stocker operations should also take into consideration the regional origination of cattle received, Yazwinski notes. Considerations when determining worming strategies include factors such as North versus South during the winter months and grass-fed animals versus drylot.
This is often not easy to do, but if you do have access to the regional history of the cattle coming into your operation, you can better tailor an effective parasite management strategy.
“Particularly in the Northern states,” Reinhardt adds, “for cows or feedlot cattle that go into confinement, there is an additional need for external parasite control in the fall of the year.”
Best management practices
“Regardless of where you are in the beef production industry, you should determine if your treatment is effective – if those monies you spent on a wormer were well spent or wasted,” Yazwinski says.
“The only effective way you do that is to do a fecal egg count reduction test wherein egg counts are done on at least 10 head on the day of treatment – and then again on the same 10 head 14 days later.
If you don’t get 90 percent reduction in egg counts, then you did not get ‘efficacious’ worm control and, yes, you wasted your money with the purchase of your wormer, and you lose money to worms every day post-treatment. This loss is usually not seen but assuredly ‘felt’ with less animal to sell,” Yazwinski notes.
Currently, Reinhardt says there is an interest in rotating between different product forms and molecules for parasite control. This rotation aids in minimizing the chance of parasite resistance to certain anthelmintic chemical compounds.
Fecal egg counts can also aid in the detection of parasite resistance. “If you have treated with a good [approved] product at the right dose, and you have significant egg shedding two weeks later – that’s an indication of resistance,” Reinhardt said. “You may need to consider a different type or compound.” 
— Chris Reinhardt, professor of animal science and feedlot extension specialist, Kansas State University
PHOTO: Cattle are susceptible to certain species and genera of parasites that are present almost year-round and at varying levels. Photo courtesy of Danielle Schlegel.
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Danielle Schlegel
- Freelance Writer
- Whitewood, South Dakota
- Email Danielle Schlegel
