As spring ramps up, so do parasites in livestock. Parasites, however, don’t have to take over your operation.
“Spring is typically the most active time of year for internal parasites,” Andy McCorkill, a University of Missouri livestock specialist said. “They often use the animal’s intestinal tract as a host through the winter months and then start shedding eggs through feces in the spring as the temperatures start to rise. In the heat of the summer, they really slow down as they can’t take the excessive heat very well.”
If left untreated, parasites can seriously impact the health of livestock.
“(Oklahoma State University) reported a study in the mid-1990s for the Marshall Research Station that demonstrated a 20-pound increase in weaning weights of calves treated for internal parasites, and a 25-pound increase in weaning weight for calves when both the calf and cow were treated. Parasites can compromise the immune system and allow bacterial infections to set in,” Dr. Robert Wells, livestock consultant at the Samuel Roberts Noble Foundation in Ardmore, Okla., explained. “Some fly species can take more than 30 blood meals a day per fly. Compound that by the number of flies, and this can reduce gain and animal welfare. If cattle are mobbed up in a group, there is a good likelihood they are fighting a high number of flies. This can reduce gain of the cattle as they are not eating and gaining, as well as reduce the immune status. There are several insect-borne diseases such as anaplasmosis and pink-eye that can be transmitted by ticks and flies. Reducing the number of parasites also reduces the potential for transmitting the disease.”
According to McCorkill, taking a few steps to prevent an infestation will save time, labor and money down the road.
“Like with many ailments in life, an ounce of prevention is worth a pound of cure,” he said. “Taking efforts to reduce contact with internal parasites will help reduce the likelihood of having parasite problems in the first place.”
While there are chemical controls on the market, Wells said a “natural approach” could be affective against parasites.
“Rotating pastures to graze and allowing a duration of rest longer than the lifecycle of the fly you are trying to avoid will reduce available host sites. Horn and face flies require fresh manure to lay eggs. If the larvae hatch and there is no new host material to lay eggs in, it can break the life cycle of the fly,” he said. “For internal parasites, keep forage length high to reduce the ability of the worm parasite larvae to migrate up high enough on the plant leaf while it is wet to be ingested by the cow. Rotating pastures will also help break the life cycle.
To treat external parasites, McCorkill said there is not a “one-size fits all” answer, but he did offer three common methods of treatment:

1. Feed through additives such as Altosid

“Altosid works well if started early because they break the life cycle of horn flies in particular,” he explained. “Unfortunately, it doesn’t work with all types of flies and other external parasites so it is limited in its usefulness. Furthermore, flies don’t respect boundary fences; if you have cattle against a neighbor who doesn’t feed Altosid, his flies could find their way to your cattle.

2. Fly tags

McCorkill said fly tags are a good choice to control flies and other external parasites that congregate around the head of the animal, but their range of effectiveness doesn’t generally provide control for the whole body, leaving room for udder or underline infestation. “Flies have the ability to adapt resistance to chemical treatments relatively quickly so steps must be taken to reduce the likelihood of developing resistance to a particular chemical compound,” he said.

3. Pour-on, spray, back rubber and dust bags

“They share many of the same active ingredients as the fly tags so they carry the same caution about resistance issues,” McCorkill said. “With adequate coverage, they do provide fly control for the entire body, which is a nice feature. Perhaps the biggest drawback is the duration of efficacy; it is quite variable based on precipitation, but in general is much shorter lived than the fly tags and diligent use of feed through methods.”
“It is best to rotate classes of chemical or drug that is used,” Wells said. “Use two methods of control during high external parasite infestation times, such as backrubs, feed-based, sprays or ear tags for external application. “
“The problem we often run into with pour-ons for internal use is getting it applied in a manner that allows the product to soak into the skin,” McCorkill added. “In order to get it to work, the use of an applicator placed as close to the animal’s skin as possible is imperative. The hair coat sometimes gets in the way. Pour-on products also require some ‘dry’ time to soak in. It isn’t advisable to treat livestock when rainy weather is in the forecast. Products labeled for both internal and external parasites available in a pour-on formula include doramectin, eprinomectin, ivermectin and moxidectin, to name a few.”
McCorill added that he generally advises livestock producers to use the method that is closest to the major parasite threat. If external parasites such as lice, ticks, flies and the like are the major problem, a pour-on application is probably going to work better, whereas if internal parasites are more serious, an injectable product will be more advisable. “Sometimes, it makes sense to use an injectable dewormer and still utilize some sort of more targeted pour-on product to control external parasites. It really depends on the situation,” McCorkill said.


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