Cattle Today

Cattle Today

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Dr. Steve Blezinger

Management and control of parasites, both internal and external, in beef cattle can be a time consuming, expensive and frustrating process. In Part 1 of this series we examined internal parasites such as stomach worms, etc. and found that the key to controlling these critters is breaking the life cycle. In this issue, let's take a continued look at control of these internal pests and what the cattleman can do to take control of this situation.

Control in Pasture Environment

Pasture control must be directed at controlling the free-living stage of internal parasites in cattle. To do this, keep large numbers of infective larvae from accumulating by reducing contamination of pastures at critical times during the grazing season. By understanding the life cycles of these parasites and predicting the times during which large numbers normally occur, you can reduce intake of large numbers of infective larvae by removing susceptible cattle and not placing them on highly contaminated pastures. Clean and safe pastures are terms used to designate pastures with few or no free-living larvae. Examples of clean pastures would be those permanent pastures not grazed for a long time. In the Southern United States, larvae may live in the soil for extended periods in winter and summer if the weather is favorable. Examples include pastures used for temporary grazing, both summer and winter, where extensive tillage is carried out. Safe pastures are described as those with low enough infective worm larvae numbers to cause a low adult worm load. Permanent pastures that have been used for hay should be safe pastures. Permanent pastures with high contamination in the spring may become safe in hot, dry weather. Management practices used to break up and scatter manure piles will allow worm larvae and eggs to be exposed to heat and dry conditions, thus reducing contamination. However, this practice may increase the numbers in early spring or fall when conditions are more favorable for the free-living larvae to survive and infect susceptible cattle. Long grazing seasons and year-round larvae survival make pasture control more complex. The critical periods are after hot, dry summers when existing adults and also inhibited Ostertagia mature and produce large numbers of eggs. If older cattle are not dewormed at this time, a dangerous build-up takes place and will continue during autumn and winter. Young, susceptible cattle may need additional treatment to prevent infections that carry over into spring. Most calves are weaned or marketed at this time of year and the responsibility of control changes. In Type 2 Ostertagia infections triggered by better larvae-surviving weather, treat cattle before this condition occurs. Not only does this prevent damage to the stomach of the yearling cattle, but it also helps prevent pasture larvae build-up.

Control in Dry-Lot Environments

There has been some controversy about the incidence of internal parasites in feedlot cattle. According to the life cycle where infective larvae are being picked up on blades of grass in moisture drops, infection should be impossible. If infected cattle are not treated before being placed in feed lots infection should not increase. The performance of these cattle can still be reduced and they should be treated on entry. Inhibited Ostertagia sometimes show severe symptoms in the feedlot and should be treated with an effective dewormer. The dry lot can be very effective immediately after treatment to prevent recontamination before placing treated cattle on clean or safe pastures. It might be noted here that this classification could also include cattle being fed for show purposes where they are kept primarily in a dry-lot area.

Control in the Animal

Control of internal parasites in cattle must kill all stages in the animal and help control the number of larvae and eggs on pastures. Adult cattle have more resistance to internal parasites than younger cattle. But deworming older cattle will help keep down pasture contamination. Strategic parasite control has been recommended by parasitologists and dewormer manufacturers. One recommendation suggests deworming in January, April and July. January or midwinter treatment is given because cattle are stressed by weather and possibly by poorer nutrition, pregnancy or nursing a young calf. These conditions may reduce the brood cow's resistance to internal parasites. This treatment will also reduce pasture contamination, and calves should be exposed to fewer infective larvae. Early spring (mid-April) treatment is recommended because adult worm populations peak at this time. As weather conditions get warmer and dryer, infective larvae are less likely to complete their life cycle and many will be killed. This decrease in pasture contamination helps make a safe pasture. The midsummer treatment given in mid-July should be the most effective. Life cycle activity of the larvae on pasture is very low; cows and calves are dewormed; and pastures should remain safe until cooler, wet weather. This is also the best time to treat for inhibited Ostertagia. Grub treatment can also be given at this time. Another type of strategic deworming program used mainly in young cattle is deworming two to four times every three to five weeks, depending on which dewormer is used. Normally, controlling parasites in cattle is done at the convenience of the producer. We talk about the cost of the dewormer, but most cattle aren't dewormed because of the trouble of penning and working, which is a big part of the cost. The producer who has adequate, convenient facilities does a better job of internal parasite control in cattle. Combining the deworming with other health and management practices will make it all more cost effective, as long as cattle are not overly stressed. In cow/calf operations, calving season will determine when cattle are worked, and deworming treatment should be an important part of the process. Other recommendations are to deworm calves at 200 to 250 pounds and three to four months of age. This would fit the early spring schedule with fall calving or midsummer with spring calving. Deworm calves again at weaning and repeat in three to five weeks, depending on the type of dewormer used and whether calves are placed on a safe pasture. Deworm stocker cattle at turnout with a dewormer effective against Ostertagia and repeat in three to five weeks if the cattle are not placed on a safe or clean pasture.

Deworming Products

One time when I was in graduate school, my major professor asked me what we had planned for the day. My response, having grown up in Central Texas, was that we were going out to process and “worm” the research cattle. His response was “What, they don't have enough worms already, you're going to give them more?” Many effective dewormers are approved and available for treating internal parasites in cattle as outlined in the following table. They vary as to their effectiveness against adult and immature stages. Methods of dosing vary, and this gives the cattleman a choice as to how he may treat the cattle. For convenience, several products are available where working and handling the cattle are not required. These dewormers, in blocks, cubes, pellets and mineral mixtures, are economical and easy to use, especially in adult cows. For these products to be effective when cattle are not being fed, the cattle need to be conditioned to the feeds carrying the dewormer. This allows the cows to adjust so their consumption will be even and adequate. This is especially true where the dewormer is given in a single dose. Some of the products are given over three days and chances of adequate dosing is better. When cattle are dewormed individually, accurate weight determinations are critical to proper dosage. It is not necessary to weigh every animal, but spot weighing takes the guesswork away. If weight estimates are being used, be sure to use the heaviest weight if there is not a big difference in the weight of the cows.

Equipment to administer the individual dewormers should be accurate and in good working order. Carefully check settings and calibrations before starting and periodically check while treating the cattle. Most injectable dewormers are given subcutaneously. Use a short needle, 3/4 inch long or shorter, no more than 16 gauge. Check these needles every few animals for burrs or dullness, which may cause abscesses. Changing needles often will help prevent this and also lessen the chance of passing infections between animals. Early local reactions may occur, but most are temporary. Most producers use the loose skin along the neck for injection site. Behind and above the elbow is another good site for subcutaneous injection of dewormers, and reactions are not as bad or noticeable. Boluses or pills have been used for some dewormers. Don't use these in calves since choking or lodging in the oral cavity may occur. Dewormers in paste or jell form are very handy and easy to use, especially where small numbers of cattle are being dewormed. Place the product well into the mouth on the base of the tongue. Don't force the dewormer into the mouth because it might physically damage the upper throat or be forced into the lungs. Dewormers in drench form are probably the least expensive. Where larger numbers are dewormed, automatic drench guns are used. A curved hook is available and it is not necessary to grab the mouth as in the case with straight dose syringes, balling guns or paste guns. Use care in giving the drench dewormer to prevent spitting out or injury as with the paste dewormers. The drench gun should be adjusted and calibrated when beginning and checked periodically for dose accuracy. Some drenches must be mixed before using; follow directions closely. Periodic shaking or agitating will guarantee a consistent mixture. Overdosing is not necessary. Today's dewormers have a good safety margin, but overdosing will only add to the expense of the deworming treatment. Adequate care and storage of dewormers should receive close attention. Some dewormers must be refrigerated, others kept out of sunlight. All dewormers have an expiration date -- check this when buying the product and when using it. Overbuying by volume pressure may mean less per-dose cost, but if you buy too much, and the date expires, it will be wasted. Plan ahead and buy what is needed.

Resistance of internal parasites of cattle to some dewormers does not seem to be a problem. Failure of dewormers is normally caused by underdosing or using out-of-date or improperly stored dewormers. However in most instances I normally recommend that different types of wormers be used in a given year. In other words, if you use on type or brand in the spring, use a different product in your fall processing. This helps alleviate any doubt.

The following is a non-comprehensive list of a number of the various products commonly available to the cattle producer along with a general description. Inclusion in this listing does not imply any type of endorsement. Consult labels for precise usage directions, applications and parasite effectiveness.

As you can see there is quite a variety of products to choose from and they will vary quite a bit in price and cost per dose but often this is linked to the extent of the varieties of parasites they control. Product selection is not nearly as important as simply implementing a parasite control program.

In the next issue we'll examine more of the external parasites plus take a look at coccidia infection which becomes very prevalent this time of year.

Dr. Steve Blezinger is a nutritional consultant with an office in Sulphur Springs, Texas. He can be reached at P. O. Box 653 Sulphur Springs, TX 75483, by phone at (903) 885-7992 or by e-mail at


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