by: Stephen B. Blezinger
Ph.D., PAS

Since man has managed and produced cattle, control of internal parasites (worms, flukes) has been an issue. And while the industry seems to repeatedly discuss and address the problem, given the implications on animal health and performance, revisiting the subject is a necessity. As we enter the spring of the year we are reminded that control of both internal and external parasites may be one of the most important of the production components affected by management. Management decides: 1) whether to employ a parasite control program at all; 2) whether it is done regularly and systematically or in a hit or miss fashion; 3) what products are used in the program. All of these are extremely important decisions to make in an effective manner.

There is a great deal of information available that discusses parasite control and its effectiveness. This article will discuss the actual problems that internal parasites cause and areas in the animal where negative effects may be observed.

Some Basics
With all the issues the cattle industry faces, it becomes easy to overlook or simply discount some basic principles of animal management. One thing that every producer should remember – no matter what other factors face the cattle industry or your operation specifically, NOTHING replaces sound management practices or adherence to the basics. Things like consistent parasite control, proper nutrition, proper genetics, a good marketing plan, optimal forage quality are always important. They are very possibly even more important when conditions are challenging as they are right now given because when input costs climb, basic efficiencies must be optimized to insure the best return on investment and to insure the producer can return day after day, maintaining the productivity of the operation.

That said, a good parasite control program is critically important in maintaining animal performance and health. Consider some examples:

A. Nutrition
Internal parasites such as stomach worms (Brown, Barberpole and Small Stomach worms), intestinal (Threadnecked, Small Intestinal, Hookworms, etc.) roundworms and tapeworms are all examples of internal parasites that can create a serious drain on the nutrients that an animal should be able to absorb and metabolize effectively. Parasites such as these exist in the digestive tract and have serious effects on the digestive system itself as well as on the availability of the nutrients consumed all of which are important to animal health and performance.

One significant effect is the reduction of nutrient intake. Heavy internal parasite infestations can limit intake of feeds and forages by cattle. Whether we are looking at cows or calves the limiting or depression of intake subsequently depresses the intake of nutrients including protein, energy, minerals and vitamins. All are critical to the animal's health and well being but consider some specific effects. In the cow, energy intake is critical to the maintenance of body condition. During periods of internal parasite infestation when intake is depressed, energy intake is also depressed. This means that the energy necessary for the cow to maintain the necessary condition to calve efficiently, nurse the newborn calf and to rebreed may not be available. In similar situations this can affect the cow's mineral intake and status creating an assortment of metabolism problems that can actually affect the animal's survival. This becomes especially true in stressful conditions (cold and wet winter conditions, heat stress). A heavy infestation of internal parasites limits the animal's ability to tolerate these stressful conditions.

In the calf, a parasite load and the drain on energy intake level affects it while still in the pasture and then later in the feedlot. Calves are very susceptible to stomach and intestinal worms, especially after about 3 months of age when they start grazing more. Older cattle – 1 ˝ years or better develop some degree of immunity to many of these parasites. A variety of studies have shown that calves with internal parasite loads exhibit depressed gains. That means lower weights at weaning for those producers that market at this time. It is critical that calves make the most efficient use possible of expensive nutrients whether they are fed from a bag or a truck or if they are delivered from hay or pasture produced with expensive fertilizers and fuels. This includes the “cost” of the milk produced by the cow. In the current economic environment, it is expensive enough to produce the necessary milk for a cow to grow her calf to weaning, much less make those gains less efficient due to parasites. Cow calf producers don't often think of “feed efficiency” for the growing calf while still on the cow but we are at a time and place where this is critical.

When the calf is weaned and goes either onto pasture or into the feedlot, depressed intake of feed in general and energy specifically can have a major effect not only on gains and feed efficiency but on carcass performance as well. When an animal has decreased feed or forage intake and/or digestibility, one of the first places it shows up is in marbling score. Calves on a lower plane of nutrition may have enough energy for maintenance and for moderate muscle growth. The next step in energy utilization would be marbling. If the energy is not there, the marbling will not be deposited.

The effects seen in later life start on the ranch for these calves. One study performed at Oklahoma State University evaluated calves never de-wormed, those de-wormed upon arrival at the feedyard and finally a group de-wormed both at the ranch and at the feedyard. Those de-wormed at the ranch came 48 lbs heavier off the grass. Once they entered the feedyard better than 80% of the sick pulls were from the calves that had not been de-wormed prior to entry into the feeding program. By the end of the trial, the calves that were never de-wormed were 96 lbs lighter and showed 26% fewer grading Choice. These results showed that the long term implications of even a small parasite load were considerably lowered gains, reduced carcass quality and a depressed immune system. Any one of these can greatly reduce if not eliminate profitability. The three combined will assure a lot of red ink.

Another important factor in both cows and calves is that the infestation of parasites not only depresses intake it reduces the availability of nutrients because the parasites themselves take them up. So, a competitive situation develops between the parasites and the animal. Yet another problem is the damage done by the parasites to the mucosal and epithelial lining of the gastrointestinal tract. This damage can greatly depress absorption of a variety of nutrients in addition to the animal's blood the parasites consume. Additionally, parasites such as liver flukes can be especially damaging to the animal. Flukes damage liver tissue. Since the liver is one of the primary sites of numerous critical metabolic reactions and processes in the body, damage done by flukes can have very detrimental effects.

While this discussion only touches the surface, it becomes obvious that internal parasites, left unchecked, can have huge effects on animal performance as related to nutrition

B. Health
Another critical aspect of animal performance as affected by the variety of internal parasites is animal health. Much of this can be directly related to nutrition since nutrition and health are so closely linked. In any situation where nutritional status is depressed, a similar depression in immunity is commonly noted. This results in greater susceptibility to infection and a reduced ability of the animal's immune system to fight off pathogens.

Any situation where the immune system is compromised creates a problem. With an internal parasite load not only is there a problem with depressed nutritional status but as discussed above there is damage to the gastrointestinal (GIT) and other tissues (liver tissue with liver flukes, lung tissue with a lungworm load). This damage to the tissues, especially in the GIT and lungs create an opening in the animal's system allowing for entry of pathogens. This coupled with a depressed immune system is highly problematic. Additionally, parasites place a load on blood volume which creates yet another problem for normal metabolism in the animal. In many cases, these circumstances alone can seriously depress the animal's performance and can ultimately cause death if left untreated.

All herds go through stress of some type – heat, cold, wet, handling, transportation, etc. When an animal with a heavy parasite load that may be in a depressed nutritional and immune status is then subjected to a stressor of some type, i.e., weaned cattle transported to pasture or the feedlot, significant sick pulls and death loss can and does result. Extensive research from a variety of sources has shown that cattle that have not been treated for internal parasites make up a large portion of the sick pulls and death loss in the feedyard.

Finally, in some cases infestation by internal parasites can be severe enough to be the sole cause of death. In these cases postmortems are invaluable in treatment and control methods. Other diseases and conditions may complicate the case, and a postmortem will be the only way to determine the primary cause. Other diseases such as shipping fever complex, digestive disturbances, salmonella infection and viral diarrhea will show similar symptoms as internal parasite infection. In many cases the postmortem will show not only the disease condition but also the parasite load contributed to the death of the animal.

Some Points to Remember
There are a number of key points that every producer should keep in mind:

1) Internal parasites are a problem in every herd. Even with a very aggressive treatment and control program, it is an ongoing and recurring problem.

2) Young and older animals are more susceptible to infestation and the subsequent problems that develop. And, while older cows are more resistant, they do suffer the effects as well.

3) No treatment is entirely fool-proof. Parasites can develop a degree of resistance to the same de-wormer used continuously and therefore different products should be used is some type of rotation. It is very important to understand the products and where their strengths and limitations are

4) Treatment should be coupled with appropriate timing and placement of cattle on “clean” pastures.

5) Conditions such as drought, excessive rainfall and so on can increase a parasite problem.

6) Treatment in almost every case will be a positive investment.

As in everything, a well-managed cattle operation must adhere to good basic management practices. De-worming or internal parasite control is very high on the list of the most important basics. It is one of the practices that will, virtually every time, make or save the producer significant dollars every year.

Copyright – Stephen B. Blezinger, Ph.D., PAS – March 2017. Dr. Steve Blezinger is a nutritional consultant with an office in Sulphur Springs, TX. He can be reached at (903) 352-3475 or by e-mail at [email protected] For more information visit us on Facebook at Reveille Livestock Concepts.

Don't forget to BOOKMARK  
Cattle Today Online!