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Preventing Causes of Infection in Cattle

By Hubert J. Karreman, V.M.D.

If you’re pasturing animals in the same areas year after year, you’ve got to realize that there will be parasites waiting for each group as they arrive since many parasite eggs can survive over winter in the soil waiting for warm and moist conditions to return. Pastures look really nice early on, but those stomach worm larvae are invisible to our eyes and are rapidly multiplying and loading the animals that are out there eating the forages. Right now, unless your paddocks are scorched dry, parasites are thriving and sending millions of eggs out onto pasture as your herd animals drop their manure on the ground. The eggs hatch in a few hours, the larvae of the stomach worms then crawl up the blades of nearby grass, hoping to be eaten by animals as they graze, then start their life again in the host, sucking blood from the stomach walls. This is basic biology of the strongyle class of internal worms—which affects not only cattle, but sheep, goats, pigs, horses, and many other mam­mals—and there’s no getting around it completely.


Parasites always take advantage of the fact that animals on farms are enclosed in the same spot due to perimeter fencing or indoor stalls and cannot get away from them. Free-roaming cattle on the original prairie probably had a low level of parasitism with which they could live in balance. Parasites generally thrive under these conditions: high animal density, animals kept in the same areas continuously, nutrition­ally deprived animals, poor pasture management, and poor premises management. Coccidia are usually found in animals indoors in pens that are being continually used. Coccidia problems are not usually seen when animals are on pasture. On the other hand, stomach worms are usually found in animals on pasture (and not when continuously in­side), especially at peak and late season when the parasite population has multiplied many times.

This buildup is due to cattle reinfecting the pastures in the warm, humid months with fresh manure carrying worm eggs ready to hatch and be eaten again with pasture grass. It is critical to never have young stock follow older stock—young stock im­mune systems are not capable of withstanding parasitism like mature adult cattle can. And, importantly, Johne’s disease can also be passed to younger animals following older animals on pasture. It is very rare that adult cows need any kind of wormer at all, unless you want to increase milk production a few pounds per day. Adult cows can and do carry stomach worms but they do not become infested; check some manure samples and you’ll see. However, young stock can get hammered by parasites. Interestingly, a very low level of parasites will probably cre­ate a stronger animal than one that is routinely dewormed. Only by checking manure samples can the level of infection be known.

A cattle tapeworm, Taenia saginata, under the microscope. 3D Rendering.

Also contributing to parasitism is the harmful practice of not feeding hay to pre-weaned calves. Why is this harmful? In the search to satisfy their instinctual need for fiber, calves will eat bedding, which will likely have parasites on it. Just watch some calves for a while that do not get any hay fed to them—they will nibble the ground for fibrous material, guaranteed. Additionally, the developing rumen (which causes the instinct to want fiber) is not just a “sponge” that absorbs and passes on volatile fatty acids (supplied most quickly by grain); it is also a muscular organ that turns over every minute or two. The muscles develop more strongly with hay in the diet. Ever see bloating pre-weaned calves? Their diet is usually milk replacer and grain—no hay until after weaning.

In organic agriculture, due in part to the requirement that animals six months and older must get a minimum of 30 percent dry matter from pasture over the grazing season, it is only a matter of time before the young stock, which are not immunologically mature against stom­ach worms, will become infested if pasture management is not top-notch. A big part of pasture management is proper feeding to ensure excellent energy intake while on pasture, such as from high-energy forages or some grain. The immune system depends heavily on proper daily energy intake.

A liver fluke (parasitic flatworm) found in cattle and other grazing animals.

I think a good goal is to raise calves that do have some challenge from stomach worm larva in the pasture yet are managed and fed well enough that rather than becoming infested, they instead build immunity due to a low-level exposure. This is a kind of a natural vaccine effect. Unfortunately, not many farms seem to be able to achieve this low level of exposure. The result is somewhat stunted calves that likely will freshen a month or two later since they won’t reach breeding size as quickly. However, calves that do make it through this tough period of life—usu­ally between four and eleven months of age—start looking really nice again by a year old and go on to do fine. Even if they did look crummy due to a significant stomach worm infestation, they will now be strong against pasture stomach worm challenges the rest of their lives.

Signs and Symptoms

Unfortunately, the smaller the land base and higher the animal density, the more likely it is that parasites will infest young stock as similar groups are placed in the same small lots year after year. Animals carry­ing a burden of internal worms will suffer from lowered immune sys­tems, which can be troublesome if there are sudden changes in weather (cool damp weather will quickly trigger the calves to start coughing). Only on rare occasions have I seen an animal so severely parasitized that they are near dead due to anemia (loss of blood due to parasite action). This will present as an animal that has a swollen-looking jaw (fluid filled), very white mucous membranes (mouth, eye sockets, vul­va), and is extremely weak—most likely lying down. Sometimes these young animals will also have ulcers in their mouth.

What do your calves on pasture look like right now? Are they sleek and in good body condition, just like when you weaned them or set them out to pasture? Or do they look a bit more ragged now, perhaps a bit potbellied, their hair dry and reddish-black, not shiny black as it should be? Do they have thin back-leg muscles and dried diarrhea high on their legs and tail? If so, these are classic signs of internal stomach worm infestation.

It would be wise to catch up a few calves and look in their eye sock­ets to see how pink or pale white the sockets are. In sheep and goats, it is common to use the FAMACHA (Faffa Malan Chart) test, which involves looking at their eye sockets. How white the sockets are, in­dicating anemia, will indicate when to treat them with a conventional wormer. While the FAMACHA test is technically not valid for calves, looking at their eye sockets will nonetheless reveal the degree of blood loss. Calves just hide it until later in the disease.

Remember, really check your young stock on pasture for signs of in­ternal worm infestation. If they are infested and nothing is done about it, the first batch of damp cold weather will likely bring on pneumo­nia—and that is not at all desirable. So be mindful: stop and observe your animals and take action as needed now, not later.

Prevention and Treatment

As the summer progresses, remember to address parasite prevention and treatment in young stock from a multipronged approach, which is a logical response because:

  1. A variety of approaches for any problem will give a better chance of success;
  2. If one pillar of the multipronged approach isn’t working, the other factors are still in place;
  3. Natural treatments can work well; and
  4. There will be less chance of resistance developing.

If you are used to giving calves a systemic wormer (like ivermec­tin or moxidectin) and you replace it with some natural wormer, this would be what is called “input substitution,” the opposite of a multi­pronged approach. What we really need to do is understand the biol­ogy of the parasites that like to live in or on cattle and then figure out where to break their life cycle. Only after that can we go on to use a botanical mixture to substitute for the typically used synthetic wormer.

Source: Four-Seasons Organic Cow Care