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Home , Morantel, Ostertagia ostertagi, Parasitic disease

Research Information Sheet #104 August 2001

IINTERNALNTERNAL PPARAR ASITES ASITES OF OF CCATTLEATTLE ININ LLOUISIANAOUISIANA AND AND OOTHERTHER SSOUTHERNOUTHERN SSTATESTATES

J.C. Williams and A.F. Loyacano

Introduction...... 2 The Parasites ...... 3 Harmful Effects of Internal Parasites in a Herd ...... 5 Recognition of Internal Parasites as a Problem in a Herd ...... 7 Transmission of Parasite to Cattle ...... 8 Inhibition of Larval Development - Ostertagi ...... 10 Prevention and Control of Internal Parasites ...... 11 Grazing Management ...... 11 Use of De-wormers in Control ...... 12 Systematic or Strategic Use of De-wormers ...... 13 Improved Cattle Resistance to Parasites Through Management and De-wormers ...... 14 in Cattle ...... 15 Treatment Recommendations ...... Internal Parasites of Cattle in Louisiana and Other Southern 16 States 1 Introduction production in the South is highly trointestinal parasites can cost the intensified and internal parasites are producer from $25 to $200 per Cattle of all ages, but particularly present in an environment that is (Smith Kline Beecham young cattle, are affected by a highly favorable to their propaga- Animal Health, 1991). Even at the diversity of internal parasites. Among tion, it is likely that productivity can lower estimate, this translates into a these are the roundworms (Nema- be enhanced or substantially im- $2.5 billion loss to the cattle indus- todes), which are primarily parasites proved by parasite control measures. try each year. Obviously, all 90 of the gastrointestinal tract (a lung- Determination of accurate million to 100 million cattle in a worm is included), the estimates of production losses to given year are not treated, but the (Trematodes), tapeworms (Cestodes) cattle internal parasites is difficult to fact that some may be treated more in the small intestine, and single- achieve. Illness and are than once per year likely balances out celled protozoan parasites () obvious, but effects on weight gain, the estimated numbers. in the lower intestinal tract. Climatic feed conversion, reproductive perfor- Two examples of how anthel- conditions through most of the mance, cost of drugs and other mintic treatments can favorably southern region of the U.S., includ- medications, and other factors are affect weight gains in stocker beef ing Louisiana, provide for long more complex to assess. At varied cattle in comparison with untreated grazing seasons; however, these same intervals, national estimates of loss to control calves are shown in Table 1. conditions provide an ideal setting internal parasites, external parasites In all cases, the effect of treatment for internal parasites. Periods of or other disease entities are issued by by far exceeds the cost of treatments. greatest risk occur from governmental and other agencies. Such results have been observed late winter through spring and again For records of 1994-1995, there invariably with different anthel- in the fall. Considerable infection were 103.8 million cattle in the mintics in the two examples and in may also occur during milder winters United States valued at $66.5 billion many other LSU Agricultural Center and during summers that are very (Agricultural Statistics, USDA, research studies. It should be re- wet and not overly hot. Under 1996). American pharmaceutical membered, however, that even pasture conditions, it is the rule to companies estimated that gas- though are indispens- encounter mixed infections with several types of roundworms as well as with other parasites indicated TABLE 1. Weight gains (lb.) of cattle treated with different anthelmintics above. Because of their wide distri- compared to untreated control cattle bution throughout the southern Example 1. Treatment least square means for body weight (lb.) of cattle treated on region, the large numbers of cattle study days 0 (Jan 11) and 84 (Apr 5) infected, and the damage caused by the worms, nematodes are consid- Treatment - All Study Day ered to be the most economically Groups n =18/gp 0 28 56 84 112 140 160 important group of internal parasites Untreated controls 477ab 486 a 508 a 539 a 592 a 638 a 689 a in cattle. inject. 469a 521 b 574 b 631 b 730 c 777 c 818 c The progressive cattle producer inject. 482b 526 b 570 b 620 b 713 b 759 b 807 b today generally has a high level of Ivermectin pour-on 466a 515 b 563 b 623 b 702 b 757 b 796 b understanding of factors that can cut Different superscript letters in columns indicate significant differences (P<0.05). into efficiency and profits in produc- tion. In spite of this, there are many Example 2. Bodyweights (lb) of untreated control cattle and cattle treated with a who still underestimate or ignore the pour-on endectocide on study day 0 (Jan 18) effects of internal parasites on cattle Treatment – All Study Day Total Value @ Value/ productivity and health. Under Groups n=15/gp 0 28 56 84 112 gain $.7135 control certain conditions of management, such as with low stocking densities Untreated controls 481a 557 a 638 a 719 a 762 a 281 543.69 — and high levels of nutrition, it is Doramectin 484a 587 b 683 bc 764bc 807bc 323 575.79 32.10 often difficult to demonstrate that Ivermectin 481a 582 b 668 b 744ab 788ab 307 562.24 18.55 Eprinomectin 485a 586 b 685 bc 765 bc 812 bc 327 579.36 35.67 control methods for internal para- 485a 593 b 696 c 778 c 823 c 338 587.21 44.52 sites are warranted. However, under most circumstances, in which cattle Different superscript letters in columns indicate significant differences (P<0.05).

2 Internal Parasites of Cattle in Louisiana and Other Southern States able in parasite control, other factors, The Parasites such as a good nutritional level and general management, are also indis- Several genera and species of brown or medium stomach worm, pensable. When control of gas- nematodes are commonly found in considered to be the most harmful trointestinal nematodes and lung- cattle of all ages in the southern and economically important parasite worm is combined with a planned region. As pointed out earlier, the of cattle in temperate areas of the and systematic effort to simulta- nematodes are the most common world (Figure 1). More will be said neously control the liver fluke (where and numerous of the internal para- later about a seasonal variation in applicable) and ectoparasites, (i.e., sites of cattle in the southern region development of this parasite that can , lice, grubs, etc.), productivity and, consequently, more of a threat result in severe parasitic problems. will be increased. Good control of for disease and production loss than Also present in the abomasum are any of the parasite groups just other internal parasites. Largest axei, the stomach indicated can result in increased infections are usually found in hairworm, and Haemonchus sp., the productivity, depending on preva- weanling and yearling cattle. The large stomach worm or barber pole lence in a given geographic area; worms are parasitic in different worm. however, good control of all para- portions of the gastrointestinal tract. Among worms in the intestinal sites along with good overall herd The abomasum or true stomach is tract are several species of , health is the best guarantee of the site of Ostertagia ostertagi, the Strongyloides papillosus, Trichos- increased productivity. A B

Figure 1. Ostertagia ostertagi: The medium stomach worm of cattle. (A) Adult male parasite, approximately ½ inch long and early C 4th-stage larva, less than 1/16 inch long. (B) Yearling calf with severe Ostertagia infection – note rough hair coat and bottle jaw. (C) Calf with similar condition in chute – note severe . (D) Calf abomasum showing “Morocco leather” appearance due to heavy Ostertagia infection. D

InterInternalnal ParasitesParasites ofof CattleCattle inin LouisianaLouisiana andand OtherOther Southern States 3 trongylus colubriformis, Nematodirus small intestine but are not known to helvetianus, cause any ill effects. phlebotomum, the , The prevalence of radiatum, the infections in cattle throughout the nodular worm, and sp., the region is high. Surveys and other whipworm. The cattle lungworm, studies of apparently healthy cattle Dictyocaulus viviparus, is found in (beef and cows, yearling steers, the large and small air passages of replacement heifers, and calves) the lungs. It is the only lungworm generally reveal infection levels of commonly found in cattle. The liver 80% and greater as indicated by fecal fluke () occurs in egg counts and post-mortem exami- the liver tissue (larvae) and bile ducts nation. As mentioned earlier, level of (adults). Nearly all of the worms are is greatest in young cattle; rather small and delicate, ranging adult beef and dairy cattle generally from a fraction of an inch to more show little evidence of nematode than an inch in length. In contrast, infection or disease unless stressed by tapeworms of cattle (Moniezia spp.) nutritional deficiency or other can grow to very large size in the diseases.

A B

Figure 2. Damage caused by gastrointestinal nematodes in cattle: intestinal tissue showing some slight hemorrhagic condition and (A) Hemorrhage caused by large stomach worm Haemonchus. (B) thickening of mucosa as caused by Cooperia spp. (D) Lower small Less obvious reddened areas due to smallest of the cattle stomach intestine showing nodules caused by larvae of the nodular worm – worms – Trichostrongylus axei. (C) Section of duodenal/upper Oesophagostomum.

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4 Internal Parasites of Cattle in Louisiana and Other Southern States Harmful Effects of loss of serum albumin from the for reasons not clearly defined. Since Internal Parasites in a blood, reduced acidity, and severe many of the different types of worms diarrhea. The large stomach worm may occur in cattle at the same time, Cattle Herd (Haemonchus) is an avid blood their individual and collective dam- The means by which nematodes sucker as is the intestinal hookworm, aging effects are not difficult to inflict damage on the host and Bunostomum. Worms in the intesti- comprehend (Figure 2, Figure 3). nal tract (Cooperia, Trichostrongylus, consequently cause disease and For a long time it was thought reduced productivity are not well Nematodirus) can all cause damage that the primary effect of nematode to the intestinal lining when present understood. Different nematodes infection on the host was interfer- may penetrate and migrate in tissue, in large numbers. The lungworm can ence with digestion and malabsorp- suck blood, or otherwise cause small cause severe disease and deaths tion of nutrients. Considering the primarily from the effects of pneu- hemorrhages, cause erosion of basic digestive and absorptive func- surface layers of the gut lining, or monia and asphyxiation. Liver tion of the gut and the mechanical condemnation is a major loss caused incite formation of nodules. The and possible chemical damage medium stomach worm (Ostertagia) by damage due to the liver fluke. inflicted by parasites, the association can extensively destroy vital digestive Besides , serious production appeared to be appropriate. Recent losses can be attributed to the fluke cells of the abomasum, resulting in evidence has shown that damage and

A B

Figure 3. Further examples of damage caused by parasites in calf with severe lungworm infection – note head down, tongue out cattle: (A) Section of mid intestinal region showing some areas of and animal “gasping” for breath. (D) Cut section of lung showing thickening and hemorrhage as caused by the hookworm mass of thread-like lungworms and yellow host exudate. Note Bunostomum and other worm species. (B) Cut section of liver lighter normal tissue in contrast to deeper red areas in lung tissue showing opened bile duct region with flukes present. (C) Yearling and purplish color on lung outer surface. C D

Internal Parasites of Cattle in Louisiana and Other Southern States 5 inflammation of the lining tissue of completely than untreated controls. though they need less forage, they the gastrointestinal tract results in The aerial photograph shown in have all they want and can reach leakage and loss of blood protein Figure 5 demonstrates this difference their performance potential. This can into the gut. Such loss can drastically in pastures. The differences in mask some of the differences be- alter protein , including appearance are due to forage height tween treated and non-treated muscle growth. A major unexplained and availability because of decreased . Nematode infections, as effect of infection is loss of appetite. appetite in untreated control cattle. well as factors such as forage palat- The end result is failure to grow or At relatively high stocking rates, ability and toxicity, can also bias weight loss (Figure 4). For a number treated animals may graze pastures forage evaluation studies by affecting of years in parasite control studies at so close that they do not have forage availability and nutritive the Dean Lee Research Station near sufficient forage for optimum weight value. Replicates of different stock- Alexandria, it has been observed that gain. Animals not treated, on the ing rates may be necessary to accu- cattle treated experimentally for other hand, may have significantly rately evaluate differences. parasites graze their pastures more more available forage and, even

A B

Figure 4. (A) Weaner/yearling cattle during a wet and cold control but grazed on pasture with heavy infection risk. Louisiana winter. Note poor condition, evidence of diarrhea due to and thiabendazole were drugs used in this 1982 study, but the parasitism. (B) Abomasa from calves of different treatments in a major point is effect of pasture management in reducing infection parasite control field study – abomasum at right end is from an risk. (C, D) Comparison of a severely parasitized abomasum untreated control; the abomasum at left end is from group that (Ostertagia) on left and another from a calf on the right of similar received maximal control and grazed on pasture with little infection; age (early yearling) but not exposed to infection. the abomasum in center is from a calf that received maximal

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6 Internal Parasites of Cattle in Louisiana and Other Southern States Recognition of Internal Parasites as a Problem in a Herd

While all cattle can be expected to have some nematodes in their gastrointestinal tract, it should not be assumed that all or most cattle are adversely affected by clinical parasit- ism. Clinical parasitic disease is usually obvious; minimal or not so minimal losses in day-to-day produc- tivity caused by small worm burdens are not so obvious. Loss in produc- tivity due to inapparent or subclinical parasitism has not been accurately assessed, but most evidence indicates that it results in greater losses industrywide than clinical disease Figure 5. Aerial photograph of pasture at the Dean Lee Research Station showing effect of outbreaks. It might be noted that treatment for parasite control on appetite in cattle. The four pastures (5 cattle on each 4- widespread use of the avermectin/ acre plot) separated by vertical lines are those of note; pasture on far left is wedge-shaped. milbemycin compounds (ivermectin, Differences in appearance are due to forage height and availability because of decreased doramectin, eprinomectin, and appetite of untreated and parasitized control animals. Pastures occupied by treated animals moxidectin), with their highly are lighter in color, while the control pastures are darker green, indicating a greater amount and density of forage. efficient activity and persistence, has generally reduced the occurrence of acute parasitic disease outbreaks. diseases. The producer who sees his evaluating all factors involved, Recognition of nematode para- cattle regularly can often judge including clinical signs of parasitism, sitism, whether it be a clinical disease whether such problems exist. differentiation of parasitism from outbreak or subclinical inapparent Besides early recognition of other disorders/diseases, deficient parasitism and reduced productivity parasitism, which can help in reduc- nutrition, and the relationship of in a herd, is a key factor in any ing further loss and preventing management and weather factors. approach to prevention and control continued contamination of pasture Two techniques that a veterinar- (Figure 6). The classical signs of with worm eggs, an evaluation of ian may use to help in diagnosis are severe parasitism such as progressive general management, grazing fecal examination for parasite eggs weight loss, diarrhea, rough hair history, and weather factors is and post-mortem examination. coat, bottle jaw, and anemia are all important in determining risk of Microscopic examination of cattle too familiar. In many cases, however, parasitic infection. Nematode para- feces for parasite eggs can indicate it is necessary to rule out the possi- sitism is closely associated with what worms are present and may at bility of diseases other than parasit- certain grazing practices, and avoid- least suggest levels of parasitism. The ism or deficient nutrition. Effects of ing or altering these practices can post-mortem examination of an roundworm parasites in a herd may reduce risk. Temperature and rainfall animal or animals in a herd that die go largely unnoticed except with are also clearly related to the danger is the most direct method of deter- careful observation. Such effects may of parasitic infection under certain mining the kinds of worms present include inefficient feed utilization, grazing practices. Services of a and the amount of damage caused. delay in attainment of breeding age veterinarian are often required to Observations of the producer and (puberty), poor conception rates/ fully understand the nature of a veterinarian in many herds will pregnancy, depressed milk produc- given problem and to achieve a indicate that worms are a significant tion, and lighter calves with greater solution. An experienced herd health burden even though a post-mortem susceptibility to parasitism and other practitioner can aid producers by examination is not feasible or incon- Internal Parasites of Cattle in Louisiana and Other Southern States 7 clusive and worm egg counts are Transmission of Parasite low. “Diagnostic treatment” in such Infections to Cattle cases with an efficient de-wormer or anthelmintic can help to understand Adult male and female worms of and alleviate the problem and the various nematode genera inhabit ultimately improve overall herd different parts of the gastrointestinal performance. tract. After mating, female worms produce eggs that are passed out in feces onto the pasture. In the case of the lungworm, eggs hatch in the A gut, and first-stage larvae are passed in the feces. Hatching of eggs and development and survival of infective larvae are highly dependent on temperature and moisture. All processes are rapid in warm weather and slowed during cooler weather. High temperature and desiccation in summer and subfreezing tempera- ture in winter can effectively kill off eggs and larvae on pasture, and this often results in reduced parasite transmission during these periods. In addition, hot and alternating wet and dry periods of summer in the region are more adverse to nematode free-living stages on pasture than winter conditions. The basic life Figure 6. Cattle nematode parasite eggs and infective larvae. (A) Microscope illustration of cycle of the nematode parasites from a gastrointestinal nematode egg from fecal sample (large object at right center) and to the the time that eggs are deposited in lower left is a protozoan oocyst (coccidia). (B) The picture is “staged” but shows a large feces on pasture until infective larvae number of cattle nematode infective larvae in a droplet of on a blade of grass – this happens in nature. are available for infection and the parasitic stage in cattle is shown in Figure 7. B Infective larvae of most nema- tode species on pasture grass are swallowed with forage by grazing cattle. In the case of the hookworm, Bunostomum, and the intestinal threadworm, Stronglyoides, infection occurs when infective larvae pen- etrate the skin of cattle. This occurs on the lower portion of the legs while animals stand in muddy, fecal- contaminated areas or anywhere on the body surface when animals lie down in such areas. Larvae of the latter two worms travel by the blood to the heart and lungs and then to the intestinal tract where they mature. In the case of the cattle lungworm, eggs hatch in the cattle 8 Internal Parasites of Cattle in Louisiana and Other Southern States intestine and early or first stage larvae are Figure 7(A). Life cycle of gastrointestinal nematodes in cattle. General passed in the feces. Development of cycle of nematodes of the stomach and intestinal tract. Developmental gastrointestinal nematode larvae to the time in cattle ranges from 2-5 weeks for most, but up to 8-9 weeks for third or infective stage can occur as quickly the hookworm. as 7 to 14 days on pasture during optimal conditions (warm weather) but may be delayed for several weeks in colder weather. Once larvae reach the infective stage they can survive for several months from fall and winter to spring. This fact clearly emphasizes how large levels of pasture contamination accumulate under poor and sometimes generally good management conditions. Survival is generally shortest during summer. After infection of cattle, most of the nematode parasites develop to the adult stage in 2 to 4 weeks. Major damage in the abomasum and intestinal tract occurs Figure 7(B). Life cycle of gastrointestinal nematodes in cattle. Life cycle during the period of larval development to of Ostertagia ostertagi, including notes on the inhibited larval phase the adult stage. Therefore, with a total life that occurs in spring and summer in Louisiana. cycle, from egg to egg, requiring about 6 to 8 weeks (2 to 3 weeks on pasture and 2 to 5 weeks in the cow) during much of the year, it is possible for infections to recycle several times during a long grazing season. With constant daily infection occurring in grazing cattle during a grazing season, considerable worm burdens can develop. The life cycle of the liver fluke is far more complicated than the direct cycle of nematodes. Development of the liver fluke in the free-living environment requires an intermediate host (snail), and the free- living phase requires 10 to 12 weeks before infection can occur. The parasitic phase Figure 8. Life cycle of Fasciola hepatica, the common liver fluke in also requires about 10 to 12 weeks, from cattle. time of infection to development of mature parasites (Figure 8). In Louisiana, Texas, and Florida, most fluke transmission occurs between the months of February and July. Moisture surplus and tempera- tures during this period are most suitable for expansion of snail populations and development of immature fluke stages on pasture. Fluke transmission effectively ceases during the drier months of summer and early fall. By fall, fluke infections in cattle consist almost entirely of mature adults and, consequently, treatment is most effective at this time.

Internal Parasites of Cattle in Louisiana and Other Southern States 9 Inhibition of Larval worms cause no problems. However, usual to see the condition in older Development - Ostertagia the inhibited worms will begin to cows and bulls as well. Large num- mature to adults usually in late bers of inhibited larvae, accumulated Ostertagi August and September, a time when in stomach tissue during spring, can summer temperatures begin to mature at intervals in the fall, caus- Throughout the southern decrease. In the maturation process, ing a long and drawn out disease region, including Louisiana, the the worms increase in size about process that may result in . medium stomach worm presents an tenfold in a relatively short time, In northern portions of the additional problem, making it causing massive destruction of United States, the inhibition pattern unique from the other gastrointesti- digestive tissue of the stomach. This of Ostertagia ostertagi is different. nal nematodes because of a seasonal form of Ostertagia disease is called Larvae become inhibited in develop- variation in its life cycle pattern. Type II Ostertagia disease; its ment during late fall grazing and Weather conditions from late spring harmful effect is similar to but far remain in the stomach tissue through early fall are adverse to more serious than Type I disease. through winter (Figure 10). As a survival of infective larvae of this Type II disease is seen most com- result, Type II disease occurs from parasite on pasture and, conse- monly from August to October, and late winter into spring, and Type I quently, little or no infection with usually only a small portion of a herd disease in younger cattle occurs this parasite occurs during the is severely affected. Yearling steers during summer and fall. In the period. However, the parasite older than 16 months of age and absence of documented research, the population does not die off but replacement heifers of similar age are type of Ostertagia pattern that exists spends the period of adverse weather commonly involved. It is not un- in various parts of the country in an inhibited or arrested early (L4) larval stage in tissues of the cow’s stomach (Figures 7B and 9). The Ostertagia infection and disease pattern is closely tied in with age classes of cattle and different seasons. During late fall through winter Figure 9. Seasonal pattern of infection risk for gastrointestinal nematodes and lungworm in and particularly in early spring, cattle Louisiana and other warm temperate regions. Major infection risk occurs from late winter into spring, having remained lower or even increased during winter, following lowest levels near weaning age and up to 14 to 16 during summer and early fall. In the case of the stomach worm, Ostertagia ostertagi, adult months of age can be affected by worms predominate in winter and again in the fall, but numbers of inhibited early 4 th- stage Type I Ostertagia disease. This is a larvae increase in numbers during spring and remain in glands of the abomasum until they time of year that is basically optimal mature to adults in the fall. for development and survival of infective larvae on pasture. When infection occurs, the worms develop promptly to the adult stage in the normal time span of about 3 weeks. With heavy infection, the young cattle can be severely affected, showing substantial weight loss. It is also during spring that most of the Ostertagia larvae on pasture become conditioned by weather factors to undergo inhibition of development once swallowed by the cow. This process presumably occurs in the several weeks preceding the onset of hot and dry or wet weather of summer that kills off larvae on pasture. During the inhibited state (Pre-type II Ostertagia), the larval

10 Internal Parasites of Cattle in Louisiana and Other Southern States remains unknown. In areas such as Prevention and Control Grazing Management the central plains and in states across of Internal Parasites the center of the country from the Prevention of parasitism is Mississippi River to the Atlantic, the Eradication of worms is virtually seldom planned into grazing man- time and duration of larval inhibition impossible, but control of worms agement; however, grazing practices and disease types have not been must be a major component of cattle can affect pasture contamination defined. herd health programs, particularly in levels and risk of infection. Pastures A problem in the past has been the South. The major aim of effec- considered to have lowest levels of that older anthelmintics such as tive parasite control is to keep parasite contamination should be thiabendazole and levamisole were infections as low as possible to reserved for younger, most suscep- effective against adult worms but not minimize any interference with tible stock (weaners, stockers, against inhibited larvae of the production. replacement heifers). Reduced medium stomach worm. These drugs Effective control must be looked pasture contamination (safe pasture) were effective in controlling Type I upon not as a single approach but as can result from the following prac- Ostertagia in winter and spring but an integration of different compli- tices: pasture vacated for several ineffective in killing inhibited larvae mentary components. In broad weeks in summer for hay production, and controlling Type II Ostertagia. outline, these components in control pasture grazed exclusively by older New and improved anthelmintics systems are grazing management, dry cows (they produce far less are effective against inhibited larvae use of efficient de-wormers, and contamination than younger cattle) and will be discussed in a later enhancing the capability of cattle to for several weeks, harvested cropland section. resist infection. or rested pasture planted in annual forages, and frequent, but expensive, treatment with de-wormers. The last mentioned means could never be recommended because of ineffi- Figure 10. Seasonal pattern of infection risk for gastrointestinal nematodes and lungworm ciency, expense, and the potential of in cool temperate regions of the United States. In contrast to Louisiana and similar climatic inducing drug resistance. Since regions, the seasonal pattern of infection risk is different. Reflecting the effects of winter/ younger stock generally have highest snow cover in cool temperate regions, parasite infection is of no significance. However, at the time that cattle are initially turned out to pasture in spring, a small initial rise in infection levels of infection and produce heavy may be due to infective larvae that have overwintered on pasture. Major time of infection pasture contamination, one group of risk begins in mid- to late summer and extends into fall. In the case of Ostertagia ostertagi, young stock should not follow inhibited early 4 th-stage larvae are acquired during late fall and mature to adults in the another such group on the same following spring. pasture. A frequently asked question concerns the use of pasture rotation in parasite control. The truth of the matter is that regular rotation practice in no way reduces infection risk but may increase the risk. A 3-to 4-week rotation allows time for eggs deposited on the pasture during the previous rotation to hatch and develop into infective larvae at about the same time that cattle are reintro- duced to the pasture. Abundant, growing forage provides protection for the larvae from weather factors. Cattle in short-duration, rotational grazing programs (2- to 4-day pasture rotation) may consume a high percentage of the available larvae.

Internal Parasites of Cattle inin Louisiana and Other Southern States 11 Use of De-wormers in Control into only sparing use: morantel tartrate-(Pfizer), levamisole (Fort Development of highly efficient, broad-spectrum de-wormers since the Dodge). Decline of these products early 1960s has been of untold benefit in reducing losses to nematode parasit- cannot be definitively attributed to ism in cattle. General characteristics of all major products available to produc- drug resistance in cattle nematodes, ers since that time are given below: although activity against specific parasites (Ostertagia) decreased over Early Modern Anthelmintics time. These compounds were essen- Thiabendazole – Merial no longer makes the product tially replaced by Levamisole, Tramisol – still available, various formulations drugs (related to thiabendazole), Morantel tartrate, Rumatel – in-feed formulations released for use in the United States from the late 1970s into the 1980s, Benzimidazole Anthelmintics namely Safeguard, Fenbendazole, Safeguard, Panacur, (Intervet) oral, block, and (Intervet); Valbazen, in-feed formulations (Pfizer); and Synanthic, Albendazole, Valbazen (Pfizer) oral, in-feed formulations (Fort Dodge). These products were Oxfendazole, Synanthic (Fort Dodge) intra-ruminal injection, oral used extensively for a decade or two Besides efficacy against nematodes, all the benzimidazole drugs have and were highly active against some effect against tapeworms; albendazole provides “aids in control” gastrointestinal nematodes and for liver fluke. Fenbendazole is also available for use in lactating dairy lungworm. There was some activity cattle of breeding age. Slaughter withdrawal times for fenbendazole, against the tapeworm (Moniezia), albendazole, and oxfendazole are: 8 days (oral) and 11 to 13 days (in and albendazole offers some aid in feed), 27 days and 7 days, respectively. The effective worm killing control of the liver fluke (Fasciola). duration of these drugs is 2 to 3 days. The only drug available for All three of the benzimidazole fluke control is clorsulon, Curatrem (Merial). compounds just mentioned are still widely used by cattlemen, all retain Endectocidal Products for Endo- and Ectoparasites good activity against a broad spec- Ivermectin, Ivomec (Merial) from 1984, injectable, pour-on, 35- and trum of parasites, but all three have a 48-day slaughter withdrawal, respectively common fault of variable efficacy a- Ivomec-F or Plus (+Curatrem), efficacy against nematodes, adult liver gainst inhibited larvae of Ostertagia. flukes, and external parasites. Slaughter withdrawal time of 49 days Beginning in 1984, a new and not for use in dairy animals of breeding age chemical class of de-wormers was Ivermectin Sustained-Release (SR) Bolus (Merial), from 1997, introduced beginning with prevents infection up to 5 months after single treatment; 180-day ivermectin. While de-worming slaughter withdrawal time; not for use in dairy animals of breeding age products were always termed Eprinomectin, Eprinex (Merial), from 1997, pour-on only, no meat or anthelmintics, meaning they killed milk withdrawal worms, the new generation com- Doramectin, Dectomax (Pfizer), from 1996, injectable and pour-on, pounds were termed endectocides, not for use in dairy animals of breeding age and slaughter withdrawal meaning they had powerful activity time of 35 days for injectable and 45 days for pour-on against both “endo” (internal Moxidectin, Cydectin (Fort Dodge), from 1998, pour-on only, no meat parasites) and “ecto” or external or milk withdrawal parasites (lice, flies, ticks, mites, grubs). These products do not have activity against liver flukes or tape- Persistence of effective drug very effective and, in some cases, worms. Since the development and activity of single doses of were as harmful to the host animal as release of ivermectin (Ivomec) by ivermectin, eprinomectin, dora- to the parasites. Some of the com- Merial in 1984, two other similar mectin, moxidectin will range pounds introduced from the early products were made available for use from approximately 3 to 6 weeks. 1960s were highly useful and effec- in 1996 (Dectomax, Pfizer) and tive in their time, but either they are 1998 (Cydectin, Ford Dodge), Prior to 1960, drugs available for no longer manufactured (thiabenda- respectively. Additionally, in 1997, parasite treatment were generally not zole-Merck/Merial) or have fallen Merial introduced an exclusively

12 Internal Parasites of Cattle in Louisiana and Other Southern States pour-on product called Eprinex Systematic or Strategic as a comprehensive herd health (eprinomectin), which is related to program. It is essential when infor- ivermectin but has no meat or milk Use of De-wormers mation is available that treatment withdrawal period and is approved Inspite of all of the advances in timing be meshed in with seasonal for dairy cattle. Merial also in 1997 evolution of anthelmintic technol- prevalence of infection risk. With introduced its ivermectin sustained- ogy, there has remained a large irregular treatment, or at times when release bolus (SRB), which can tendency among producers to the herd or individuals in the herd prevent infection with nematodes for consider de-wormers as the sole or look like they need treatment, it is up to 5 months. While the older major means of control, sometimes already too late. This essentially is a products were purely synthesized to the exclusion of overall good waste of time, labor, and cost of the chemicals, the new generation, management and constant provision drug and only serves to prevent endectocidal compounds have been of good nutrition. To some extent deaths or further deterioration of derived from bacterial/fungal this policy has been fueled by those cattle condition. organisms by fermentation and selling de-wormer products, with The advantage of systemic use of further manipulated chemically. A little concern being given to timing de-wormers or strategic treatment is major characteristic and advantage of of treatments and other means of that it can be timed to mesh with the new generation products over reducing infection risk in specific some management procedure such as older ones is persistence of anti- geographic regions. The primary change of pasture. Also, de-worming parasitic activity. While killing action purpose of de-wormers is not to might be done at the beginning of a of the (fenbenda- cure sick animals, whether mildly period such as summer, when hot zole, etc.) extends maximally for or severely ill, but to reduce levels of and dry weather is most destructive about 3 days, activity of the most pasture contamination and conse- to eggs/larvae on pasture. The de- current products may extend from 3 quently prevent such episodes of wormer, along with management to 6 weeks, and as noted for the illness or reduced productivity. and weather, can be very efficient in ivermectin SRB, up to 5 months. Reducing pasture contamination cutting down losses to parasitism. This is a major advance in efficiency with eggs/larvae is most effectively The widely used spring and fall of a single treatment, that is in accomplished by some systematic treatment has much merit in that it preventing pasture contamination, timing or strategic use of de-worm- removes the large worm loads that particularly when coupled with some ers, tied in with management, such can be acquired at these times and grazing management procedure to further limit reinfection. The modern de-wormer prod- ucts, especially the newer generation of endectocidal compounds, are well suited for timely strategic treatments based on their overall high efficacy and killing activity, which lasts for 3 to 6 weeks. In some instances, a single treatment with these products is fine. In most cases, however, at least two treatments, spaced approxi- mately 8 to 12 weeks apart, for example for stocker calves grazing on winter pasture, is recommended. The ivermectin SRB, which costs ap- proximately three times as much as a single treatment with ivermectin injectable or pour-on, is capable of protecting cattle from infection completely during the southern winter-spring grazing season. Parasite control study with cow/calf herd on rolling pastures at the Hill Farm Research Station, Homer, Louisiana.

Internal Parasites of Cattle in Louisiana and Other Southern States 13 delays and reduces pasture contami- parasites or the seasonal population always result in outright disease, but nation. Treatment of all cattle a day dynamics of the worms in cattle and with heavy infections, disease prob- or two before going to pasture of on pasture in relation to weather lems may be severe. low infection risk is a must. Treat- factors and management conditions. Regardless of the susceptibility of ment at any time of year is most Such information must be known for the young or resistance of older effective when the cattle do not specific regions; it is known and cattle to infection, all age classes of return to heavily contaminated available for Louisiana and other cattle are subject to the same yearly pasture and rapid reinfection. It south-central and southeastern patterns of infection risk. In essence, should be remembered that although portions of the United States. On considering late summer/early fall as the newer endectocides have ex- this basis the most appropriate or a starting point, when infection risk tended or persistent activity, they are strategic times for de-worming is lowest, the prime or first step is to not like vaccines with unlimited treatment of cattle in different age administer de-worming treatment protection time. classes can be selected. Knowledge of for preventing the expected increase One can make decisions as to the epidemiology of nematode of infection risk from late winter priorities on what product to use parasites is also important in being through spring. Waiting for the under different circumstances, that is able to judge what pastures are of traditional spring treatment time, routine use of the best possible high or low levels of pasture con- mid-March to mid- May, can be a product for calves at the most critical tamination in different seasons. little late in achieving most efficient times such as at weaning time or use Strategic de-worming means that prevention of the spring pasture of a less expensive and active product cattle are treated at specific times in infectivity peak. Consequently, a in adult stock for primarily preven- which maximal effects can be de- second treatment at 8 to 12 weeks tive or prophylactic purposes. Pro- rived. Some particular dates for after the fall treatment, in January or ducers who do treat cattle for inter- treatment may appear to the pro- February, would be recommended. nal and external parasites have ducer to be inconvenient, impracti- traditionally done so in spring and cal, or impossible. However, most fall. This practice is associated with epidemiologically correct treatment those times when the herd was times should coincide with periods in worked for processing new calves in which de-worming is provided with spring and weaning, pregnancy other management procedures. checking, and other procedures in Cattle of all ages are exposed to Improved Cattle the fall. There is a great deal of merit the same nematode infectivity in de-worming on these occasions, potential during the course of a year. Resistance to Parasites and deviations from the pattern are The actual numbers of larvae in- Through Management rare except in cases where emergency volved in such seasonal changes, and De-wormers treatments may be warranted. Even however, will vary from high, under though these treatment times are poor management conditions, to low Up to a year of age cattle de- convenient and apparently most under conditions of good manage- velop little resistance to worm practical, they are not necessarily the ment and parasite control. Basically, infections, but after this they can most efficient and cost effective times under poor or good parasite control develop resistance to several worms to prevent and control parasitism. measures, highest rate of infection and their effects. The best possible A key word in parasite control is begins during late fall and increases level of nutrition is a key factor in prevention, preventing the danger- to peak levels in spring. Keep in providing for development of resis- ous buildup of larval contamination mind, however, that with good tance. Fertilization, weed control, on pastures that can lead to subclini- parasite control, numbers of larvae use of best adapted forages, and cal parasitism (the unseen variety in and effects of parasitism are reduced. maintenance of stocking rates to which productivity is lost) and As indicated earlier, young cattle up keep forages maximally harvested, clinical parasitism, which can cause to a few months post-weaning are provide excellent nutrition. Use of great productivity losses and deaths. susceptible to Type I Ostertagia de-wormers at strategic times which It has long been considered that disease, and yearlings, replacement reduce pasture contamination can most effective and rational preven- heifers, and older stock are affected substantially reduce infection rates tion and control of parasitism must by Type II disease. Infection with and enhance cattle resistance to be based on epidemiology of the the medium stomach worm does not infection.

14 Internal Parasites of Cattle in Louisiana and Other Southern States Drug Resistance in Cattle parasites. In some instances treat- ceived or real, but the potential Nematodes ment may be given once a year. In exists with overuse and indiscrimi- such cases, conditions for resistance nate use of de-wormer compounds. Drug resistance in nematode selection would be essentially nil. There is a general tendency today parasites of and , includ- However, in some cases, where that increased numbers of cattle are ing resistance even to new multiple treatments may be given in being treated more frequently than endectocidal compounds, has be- the same year to cattle in a closed before because of ease and conve- come a major worldwide problem, herd, conditions for drug resistance nience of modern drug formulations, most notably in Australia and New could be increased. Recommenda- for example injectables and pour-on Zealand, but also in South America, tions for strategic treatments call for products. If two or three treatments Europe, Africa, and the United two or three treatments per year, are given to the same cattle in a year, States. Increasing evidence for its particularly for cattle from weaning it would be appropriate for one of existence for some nematode para- through 16 to 18 months of age. the treatments to be with a drug of a sites of horses has been reported, This level of treatment, if deemed different chemical class from that of and drug resistance for some worms affordable, feasible, and profitable, the other two treatments, for ex- of swine has been observed in should not enhance development of ample fenbendazole for one and an Europe. There is little evidence to drug resistance. Availability of the endectocide for the other two. support drug resistance in cattle newer endectocidal products with Costs to industry to develop new nematodes, but experts in this persistent anthelmintic activity could drugs, chemicals, or other parasite field warn of the potential for it to allow for only one or two treatments control agents and bring them to occur. In the last decade or two, per year in young cattle. In the case marketing are astronomical. It is there has been only the occasional of the ivermectin SRB only one therefore imperative that the high report about one species of worm or treatment should be given to young efficacy of today’s excellent de- another being resistant to effects of a cattle. Drug resistance in cattle wormers be protected as much as particular drug. In recent years, nematodes is not a problem, per- possible through judicious use. there have been several reports of cattle nematodes being resistant to benzimidazole drugs as well as to endectocides in New Zealand. This is a very localized situation and may relate to management and treatment frequency. Cattle, for the most part, are not managed as closely and intensively as sheep. Most notably, cattle have never been treated for parasites at the frequency sheep are treated. It is generally agreed that cattle nema- todes have a genetic makeup similar to those of sheep for drug resistance selection. However, there are a number of complex factors involved besides treatment frequency, such as general differences in management of cattle and sheep, differences in grazing behavior, and differences between rapidly disintegrating sheep fecal pellets and the larger, more compact, mass of cattle feces. A large percentage of cattle on farms or ranges, especially very small Yearling cattle on 5-acre pastures in worm control experiment at the Red River Research herds, may never be treated for Station, Bossier City, Louisiana. Internal Parasites of Cattle in Louisiana and Other Southern States 15 Treatment Research on nematode parasites in stockers and replacement heifers of cattle over many years in the and to reduce pasture contamina- Recommendations Louisiana Agricultural Experiment tion. Three treatments with benzimi- Station at northern, central, and dazole drugs at 4- to 5- week inter- The question of treatment southern locations in the state has vals from the time of weaning might recommendations for prevention indicated that weather conditions of be substituted for, and achieve the and control of gastrointestinal October through May provide same level of control as, the treat- nematodes of cattle is one that optimal circumstances for develop- ment levels spaced at two to three requires consideration of many ment and survival of nematode free- months apart. With the newer factors. Under the climatic condi- living stages or high infection risk on endectocide products and their tions of Louisiana and other states pasture. Therefore, it is this period persistence of anthelmintic activity, along the Gulf of Mexico, which are that must be the focus of prevention frequency of treatments is reduced. highly favorable to parasite propaga- and control programs. The period is As indicated earlier, the worm-killing tion through most of the year, it is very long and coincides with best activity of the endectocides extends not a question of whether to treat, forage production on pasture, that is for 3 to 6 weeks, rather than the 2 to but when are the best and most winter annuals and spring growth of 3 days for benzimidazoles. economically beneficial times for perennial forages such as bahiagrass Endectocides for winter-spring treating cattle. Some of the factors and bermudagrasses. Under these control could thus be given to that must be considered are type and conditions, a single treatment of stockers and replacement heifers at level of management of forage and cattle in the fall is generally not weaning and 10 to 12 weeks later for cattle, history of problems with sufficient to protect them from effective protection and control parasite infections, the large variety increasing reinfection for the entire through spring (Figure 11). of available anthelmintics or winter-spring grazing season. The The following treatment recom- dewormer products that vary in exception to this would be treatment mendations should be appropriate formulation or means by which they in fall with the ivermectin SRB. for most cattle enterprises in Louisi- are administered (drenches, Among the different cattle age ana and south-central and southeast- injectables, pour-ons, boluses, in- classes, stocker calves and replace- ern sections of the United States. feed medication), spectrum of ment heifers require the most atten- efficacy against internal and external tion regarding parasite control parasites, cost, and overall herd Mature Cows programs. From the time of wean- health objectives of the producer. July-August: Most effective ing, these cattle are expected to There are probably a few pro- time for removal of parasites and make maximal gains. Recommenda- ducers who never treat their cattle reducing rate of infection. During tions were, and remain, that such for internal parasites, while a few the heat of summer, treatment can cattle require two or possibly three others may treat on a salvage basis remove adults and larval stages of treatments with benzimidazole only when parasite problems are nematodes including Ostertagia- drugs, fenbendazole, albendazole, or obvious or suspected. A majority of inhibited larvae. Thus, parasites in oxfendazole, to adequately protect producers probably treat for internal the cattle are removed at a time them from the time of weaning in parasite control at least once a year. when hot and dry or alternating wet the fall through spring of the follow- Many may follow the traditional and dry conditions act to kill parasite ing year. Such treatments are war- practice of herd treatment during eggs and larvae on pasture. Potential ranted at weaning in September- spring and fall. Information about reinfection is greatly reduced after November and again in the spring treatment for internal parasites may the summer treatment and can have (April-June). A third and possibly be obtained by producers from lasting effect well into fall, if the optimal treatment time is late winter several sources, including veterinar- cattle are not placed on a contami- (February-March). With the short- ians, university extension personnel, nated pasture. If mature cows are to term killing action of the benzimida- drug company representatives, be treated only once a year, this is zole drugs, length of the winter- agricultural consultants, friends, the best time to do it. spring grazing season and general television, magazines, and other In areas of liver fluke prevalence favorability of weather conditions for media. More often than not, specific (bottomlands of Mississippi and Red parasite propagation, the multiple or general times of treatment are not rivers and coastal marsh areas), treatments are necessary to achieve included with recommendations for treatment may be moved forward to an adequate level of parasite control a given product. late August to allow flukes acquired 16 Internal Parasites of Cattle in Louisiana and Other Southern States 16 Internal Parasites of Cattle in Louisiana and Other Southern States September 15-November 15: A Traditional fall treatment. This treatment time is usually more convenient than the two indicated earlier because it usually coincides with weaning for spring born-calves. Nematodes, flukes, and ectoparasites can all be controlled by treatment at this time. However, Ostertagia- inhibited larvae (from accumulation in cattle during spring-summer) would have largely matured to egg- laying adult worms in August- September, and fluke infections may have been transmitted with mild and Figure 11. Seasonal pattern of infection risk with gastrointestinal nematodes and lungworm wet fall weather. Thus, before this of cattle. (A) The natural seasonal infection risk pattern with nematode parasites in treatment, there would be some Louisiana. Peak levels occur from late winter into spring, decrease in the warmer months, and begin to increase again in the fall. (B) Effect of anthelmintic/de-wormer treatment as interval of time in which these commonly used in the spring and fall. Parasite infection is not eliminated totally, but it is parasites could have some ill effect greatly reduced, and profit should be realized rather than economic loss. on the cows and also produce more pasture contamination and increased infection risk for new calves. B February 15-April 1: Traditional spring treatment. This treatment is usually given prior to the breeding season. Again, this is a more convenient time for many producers who may have to schedule work around row-crop farming or other non-livestock enterprises, but it is not the best time for parasite control. Treating at this time will remove parasites from the cattle, but the parasites have had all fall and winter to adversely affect the cows and contaminate pastures with eggs/ in the previous spring to reach a January-February15: Elimina- larvae. If this is the only annual maturity level that will ensure effec- tion of parasites when cattle are treatment to be given, very high tive treatment. Treatment with any of most likely to be stressed. Treat- parasite populations can have accu- the pour-on endectocides at this time ment at this time removes parasites mulated in animals and on pasture, would control cattle grubs and lice and should help in reducing suscepti- the latter posing a significant infec- and provide some short-term reduc- bility to infection when animals are tion potential for new spring calves tion in horn populations. Spring- already under nutritional, environ- or fall-born calves. Treatment at this born calves, of which the producer mental, and gestational stress. This time, in combination with a late plans to retain ownership, can be treatment would also reduce pasture summer or fall treatment, can be a treated for nematode parasites at this contamination levels, which other- very effective parasite control pro- time also and given routine calfhood wise would be available to infect fall- gram. However, if the only annual vaccinations. The calves would be born calves with mother cows or treatment is given early in the year, it treated for parasites again at weaning spring calves that would soon be is not the time to get the most and given booster vaccinations. born. Fluke and external parasite benefit from dollars spent on parasite Calves, generally, would not require control could also be affected as indi- control. treatment for flukes at this time. cated for the July-August treatment.

Internal Parasites of Cattle in Louisiana and Other Southern States 17 Internal Parasites of Cattle in Louisiana and Other Southern States 17 Calves gested treatments, in February- they are received to prevent intro- All calves that will be retained by March and July. Following a treat- duction and spread of infectious the producer should be treated for ment shortly before the calving disease and contamination of pas- parasites and given regular calfhood season, the heifers should be ready to tures with nematode parasites. vaccinations at 2 to 4 weeks prior to go on the regular herd treatment Home-raised calves should receive weaning. They should be re-treated schedule. these treatments prior to weaning as for parasites and given booster shots Whether spring-born or fall- mentioned earlier. Since the primary of appropriate vaccines at weaning. born, both first- and second-calf objective of a stocker program is to Whether calves are sold at heifers remain highly susceptible to convert forage to pounds of calf weaning or retained for herd replace- nematode and fluke infections and weight, as economically as possible, a ment, most producers probably do their effects. This may be more comprehensive plan for parasite not treat nursing calves (3 to 6 obvious in first- calf heifers, but in control should be a major part of the months old) for parasites prior to many instances, it may be considered program. weaning. Spring-born calves would that the second-calf heifer is mature Spring-born, fall-weaned calves generally not begin to acquire enough to have developed resistance that will be grazed on winter-spring nematode parasites in any substantial to infection. On the contrary, while annual pastures can be allowed to numbers until they are 2 to 3 still nursing her first calf and being in carry low levels of parasitism prior to months old. Older calves likely pick gestation with the second calf, this going on the fresh forage. They up more infection than calves born young cow is highly susceptible to should be treated with an endecto- later in the calving season. Infections and should be cide 2 or 3 days before going on the in the spring-born calf can build up protected from effects of parasitism winter pasture. Thus, the calves will to sizeable numbers by June or July just as done for the first-calf replace- have potential to make excellent and would usually be highest near ment. gains when the forage is available for time of weaning. With calves to be Fall-born heifers, which should them to reach that potential. A sold or retained after weaning, be treated for parasites at weaning in second endectocide treatment at 60 treatment for nematodes in June or June or July and put on clean pas- to 80 days into a 120- to 150-day July can result in substantially better ture, may not require treatment grazing season would in most cases and cost-effective weaning weights again until just before the breeding be economically feasible. Treatment than without treatment. season in December or January. with the ivermectin SRB when the Treatment again at the end of the calves go on winter pasture could be Replacement Heifers breeding season in March or April substituted for the two treatments Spring-born heifers treated at would probably be cost effective just indicated. If grazing is to be weaning in October or November because this is during the peak continued on summer forages after with an endectocide and flukicide transmission period. Treatment with the winter pasture is depleted, and put on a relatively clean pasture the ivermectin SRB in November another treatment with an or one of low infection risk should could effectively be substituted for endectocide would be beneficial be sufficiently protected from the latter two treatments. A treat- when the transition is made, in May nematode and fluke infections until ment with one of the endectocides in or June. after the first of the year. Treatment July would allow the heifers to enter Fall- or spring-born calves that again with an endectocide and the calving season with relatively few are overwintered on hay and stubble flukicide in late February or March internal and external parasites. After and then grazed on warm-season should ensure that the heifers enter these heifers have calved, the regular perennial pasture in spring can be the breeding season with low levels cow-herd treatment schedule should allowed to carry low levels of parasit- of parasitism. Treatment when bulls be appropriate for them, subject to ism during winter. A great deal of are removed from the breeding herd the caution indicated above for the risk, however, is involved in this. in July should effectively remove second-calf heifer. Nutritional deficiency and adverse mature and immature worms, weather conditions could exaggerate including inhibited larvae of Osterta- Stocker Calves effects of existing nematode infec- gia, and also reduce ectoparasite All newly acquired stocker calves tion, help to propagate new infection populations. One treatment with the should be given all appropriate risk, and possibly result in clinical long-acting ivermectin SRB could be vaccinations and treated with an parasitism. If this type of manage- substituted for the last two sug- endectocide as soon as possible after ment is the only option, treatment at 18 Internal Parasites of Cattle in Louisiana and Other Southern States This is not Wisconsin or Nebraska, but yearling cattle in a worm control experiment feeding on a rolled out round bale of Bermudagrass hay at the Red River Research Station, Bossier City, Louisiana. the beginning of the wintering have to be more flexible. The objec- heifers. Treatment restrictions for period with a lower cost, short- tive is to have the cattle ready to dairy cattle of breeding age, regarding duration anthelmintic could be make the most use of forage that is withdrawal time for milking, are economically beneficial, especially if available. When available forage can indicated on product labels. Safe- the cattle can be provided with provide enough nutrients to produce guard, Eprinex, Cydectin, and pasture not heavily contaminated rapid calf gains, the calves need to be Rumatel are approved for use in with parasite eggs/larvae. Use of a as free of parasites as possible to take lactating dairy cattle. longer acting endectocide would full advantage of the forage. Anthelmintics and endectocides obviously offer more benefit. De- indicated for use in parasite control pending on the supply and quality of Dairy Cattle have efficacy against the full spectrum hay and winter weather, such cattle These recommendations have of nematode parasites including the may require another treatment in been written primarily with the beef cattle lungworm and Ostertagia- late winter. When summer perennial producer in mind. All general prin- inhibited larvae. In the United States, pasture is ready for grazing in spring, ciples in this publication, however, we are limited to only two products the cattle should be treated with an have direct application to dairy (albendazole and clorsulon) with endectocide. cattle. All of the internal parasites in efficacy against the liver fluke; the Regular or fixed treatment dairy cattle are the same as those in activity of these products is largely programs or schedules should be beef cattle, and the life cycles and limited to adult flukes. Although the developed and followed for adult seasonal dynamics of the parasites in tapeworm (Moniezia) of cattle is not cows. Schedules for young grazing relation to climate are the same. known to cause any significant adverse cattle are more difficult to develop. Some of the differences in manage- effects, some producers may wish to Weather conditions, forage availabil- ment of beef and dairy cattle have to treat for this parasite. The newer ity, levels of infection risk, and other be considered, but essentially the endectocides have no activity against factors vary from year to year. treatment recommendations already the tapeworm, but the benzimidazole Therefore, control programs for discussed would be applicable, anthelmintics do have some level of stocker and replacement heifer calves especially for calves and replacement activity in removing tapeworms. Internal Parasites of Cattle in Louisiana and Other Southern States 19 The intense interest and enthusiastic participation and cooperation of John W. Knox, Professor Emeritus, Red River Research Station, LSU AgCenter, is most gratefully acknowledged. Much of the information in this publication was obtained in numerous epidemiological and parasite control experiments conducted in coop- eration with our friend and colleague continuously between 1969 to 1987. Sincere appreciation is also extended to Dr. Doyle Chambers, Vice-Chancellor and Director Emeritus, LSU AgCenter, for his long-term interest and support of research on internal parasitism of cattle.

James C. Williams Alvin F. Loyacano Louisiana State University Agricultural Center William B. Richardson, Chancellor Department of Veterinary Science Dean Lee Research Station L. J. Guedry, Executive Vice Chancellor LSU AgCenter LSU AgCenter Louisiana Agricultural Experiment Station Tel (225) 578-6279 Tel (318) 473-6523 William H. Brown, Vice Chancellor and Director Louisiana Cooperative Extension Service Fax (225) 578-0400 Fax (318) 473-6535 Jack L. Bagent, Vice Chancellor and Director e-mail: [email protected] e-mail: [email protected] The LSU AgCenter provides equal opportunities in programs and employment. Visit our Web site: www.lsuagcenter.com Produced by LSU AgCenter Communications

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20 Internal Parasites of Cattle in Louisiana and Other Southern States