World association for the advancement of veterinary parasitology (WAAVP): Second edition of guidelines for evaluating the efficacy of anthelmintics in poultry.

This revision of the original poultry guidelines has been prepared to assist in the planning, conduct and interpretation of studies designed to assess the anthelmintic efficacy of drugs (newly discovered or currently used) against helminth parasites of chickens and turkeys. The original set of poultry guidelines was published in 2003. The current version provides an update on procedures to study and quantify the most important helminth parasites of chickens and turkeys, and to integrate these poultry guidelines with a new series of general, reflective and host-specific guidelines relative to assessing anthelmintic efficacy in production and companion animals. General considerations required for the conduct of studies designed to evaluate anthelmintics regardless of animal host such as the selection of study animals, animal housing, feeding, study design, record keeping and statistical analysis are for the most part provided in the newly published general guidelines. Taken together, the general and poultry guidelines should help investigators and others design and conduct studies and evaluate data concerned with determining the efficacy and safety of anthelmintics in chickens and turkeys. Additionally, this revision draws attention to several timely considerations inherent to anthelmintic evaluations such as the need to properly collect helminth specimens for subsequent determinations (e.g. species and stage verification, helminth genotyping). The investigations addressed herein, will most likely provide the very first public record of a new product's abilities to effectively reduce targeted, helminth infections in animals, and particular attention should be focused on study excellence and accuracy. Due to changes in consumer preferences, and new regulatory requirements, poultry husbandry, especially regarding laying hens, has changed immensely in many countries since the publication of the first poultry guidelines. These changes have generally allowed for a much greater exposure of birds to the source of helminth challenge (litter and fields as opposed to cages). Parasitic helminthiosis of poultry has therefore greatly increased in incidence and magnitude; changes that accentuate the need for more effective anthelmintic intervention and an update on the means of determining anthelmintic efficacy.

Distribution of Four Parasitic Helminth Species in One Pen-Free, Egg-Laying Housing Facility, and the Corresponding Efficacy of Nutraceutical and Pharmaceutical Administrations.

In the spring of 2019, adult (75 wk old) brown laying hens from a commercial, pen-free, egg-laying facility (11,000 birds per house) located in northwest Arkansas were obtained for the purposes of sourcing robust and evenly dispersed cestode infections for anticipated anthelmintic evaluations. To that end, four birds from each of six discrete sites (northwest, northcentral, northeast, southwest, southcentral, and southeast) in one production barn were obtained on two occasions, 8 days apart, and necropsied for helminth counts. A definite, repeated, location-to-location variation in infection incidence and magnitude was seen for each of the two cestode parasite species present and for one of the two nematode parasite species present. Burdens of Ascaridia galli were generally similar regardless of bird location, with site-specific mean totals per bird over both sampling days between 31 and 80. For the remaining helminths, infections were greatest for birds from the southern half of the building as opposed to the northern and from the western end of the barn as opposed to the central or eastern portions. Location-specific mean worm burdens over both sample dates ranged from 340 to 1133 (Heterakis gallinarum), 14 to 277 (Raillietina cesticillus), and 1 to 35 (Choanotaenia infundibulum). The greatest individual bird infections were 299 (A. galli), 3575 (H. gallinarum), 1015 (R. cesticillus), and 102 (C. infundibulum). The above counts are for all developmental stages combined (A. galli and H. gallinarum) and for scolexes only (R. cesticillus and C. infundibulum), as determined via standard collection and quantification procedures using both intestinal contents and overnight soaks. Immediately before the mapping study outlined above, birds were obtained from the east end of the source barn and used for the nematocidal evaluation of fenbendazole in the water (5 mg/kg body weight [BW] for 1 day), levamisole in the water (8 mg/kg BW for each of 2 days), herbal mixture in the feed (1 gm/4.5 kg BW each day for 5 days), diatomaceous earth (2% of total feed for 10 days), and a nutraceutical mixture feed supplement (2% of feed for 7 days). Based on arithmetic means for adult forms, control trial efficacies for A. galli and H. gallinarum were 0% and 12% for the nutraceutical feed additive, 0% and 22% for the diatomaceous earth feed additive, 0% and 26% for dietary herbals, 87% and 63% for levamisole, and 82% and 84% for fenbendazole, respectively. Only adult burdens of A. galli and H. gallinarum for fenbendazole- and levamisole-treated birds were significantly different from control bird levels (P ≤ 0.05).

Effectiveness evaluation of several cattle anthelmintics via the fecal egg count reduction test.

Utilizing groups of cograzed, naturally infected beef-type heifers, three fecal egg count reduction tests were conducted in the later months of 2007 at the University of Arkansas. Each test was 28 days in length consisting of individual animal fecal nematode egg counts and coprocultures. Both original and generic ivermectin injectable formulations were used in two of the tests at 0.2 mg/kg BW, with FECR percentages never exceeding 90% in either test. Oral fenbendazole was evaluated at 5 and 10 mg/kg BW, with FECR%'s exceeding 90% on all occasions, but with a precipitous drop when recently treated animals were treated at the lower dose. Evaluated in one test, injectable moxidectin given at 0.2 mg/kg BW resulted in egg count reductions of 96-92% (days 7 to 28). Also evaluated in one test, albendazole delivered orally at 10 mg/kg BW was 98% and 97% effective at 17 and 28 days post-treatment. For all tests, coprocultures conducted post-treatment contained only Cooperia spp. larvae (benzimidazole use), relatively unmodified percentages of Cooperia spp. and Haemonchus spp. larvae (ivermectin use), and primarily Cooperia spp. larvae with a small percentage of Haemonchus spp. larvae (moxidectin use).

Fecal egg count reductions and performance effect of Dectomax, Cydectin, and Cydectin plus Synanthic as used in feedlot steers.

A study was conducted to assess the effectiveness (fecal egg count reductions) and benefit (improvement in feed efficiency, average daily gain, health, and so forth) of a macrocyclic lactone (moxidectin [Cydectin Injectable] or doramectin [Dectomax 1% Injectable]) alone or in combination with a benzimidazole (oxfendazole [Synanthic Bovine Dewormer]) as used in steers upon their arrival at a feedlot. The cattle were kept in the feedlot for 181 days. Only minor differences in fecal egg count reductions were seen among treatments, with all egg counts reduced by more than 98% by 28 days posttreatment. Likewise, no statistically significant differences among treatments were seen in terms of animal performance (feed efficiency, intake, gain, morbidity, mortality, and carcass quality). All three treatment regimens appear to be comparable in decreasing nematode burdens and the consequences thereof in feedlot cattle.

Dose determination of the persistent activity of moxidectin long-acting injectable formulations against various nematode species in cattle.

The effectiveness, safety and production-enhancing benefit (improved weight gains) of moxidectin long-acting injection given subcutaneously in the ear at the rates of 0.75, 1.0 and 1.5mg/kg bw were evaluated in three studies under common protocol. The only adverse reaction to treatment was a mild (<2 tablespoons in volume), and for the most part transient (<28 days for the treatment rate of 1.0mg/kg bw) injection site swelling as noted in a minority of the animals (12.2% of the animals treated at the rate of 1.0mg/kg bw). Regardless of study site, post-treatment interval or dose rate, average daily gains were improved over control cattle by approximately 33%. Reductions in strongyle EPG counts relative to controls were > or = 90% for all dose rates of moxidectin for a post-treatment period of 42 days (Wisconsin), 84 days (Arkansas) and 140 days (Louisiana). In Arkansas and Louisiana, the majority (>80%) of post-treatment strongyle eggs, as determined by coproculture, were Cooperia spp. As determined by sequential necropsies, periods of continuous, post-treatment protection (> or = 90% efficacy in at least two out of three studies) for moxidectin long-acting injection given at the rate of 1.0 mg/kg bw were 90 days (adult Haemonchus spp.), 120 days (Dictyocaulus viviparus and adult Ostertagia and Oesophagostomum) and 150 days (Ostertagia spp. EL4).

A field trial evaluation of the effectiveness and benefit of cydectin long-acting injectable and ivomec injectable as used one time in grazing stocker cattle.

Use of moxidectin long-acting injectable and ivermectin injectable in female Bos taurus beef-type calves was evaluated in terms of efficacy (fecal egg counts) and performance parameters (weight gain). In this 150-day study, moxidectin-treated calves gained 20% more weight than did ivermectin-treated and control calves. Mean fecal egg count reductions ranged from 76.7 to 99.0 for moxidectin and -0.8 to 83.4 for ivermectin. Moxidectin long-acting injection provided efficacious (immediate as well as long-term) egg count suppressions as well as enhanced animal productivity (weight gains). The study also showed that Cooperia spp appear poised to present the most immediate challenges once long-acting macrocyclic lactone treatments become available.

Growth promoting hormonal implant pellets coated with a polymeric, porous film promote weight gain by grazing beef heifers and steers for up to 200 days.

Two studies evaluated growth promoting effects of implant pellets (IP), each containing 3.5 mg estradiol benzoate (EB) and 25 mg trenbolone acetate (TBA), to which a polymeric, porous coating was applied. Trial 1 evaluated performance of heifers (n = 70/treatment, initial BW = 188 ± 2.2 kg) and steers (n = 70/treatment, initial BW = 194 ± 2.2 kg) implanted subcutaneously in the ear with 0 (SC), 2 (2IP), 4 (4IP), or 6 (6IP) pellets that delivered EB/TBA (mg/mg) doses of 0/0, 7/50, 14/100, and 21/150, respectively, over grazing periods of 202 d (heifers) or 203 d (steers). Animals received experimental treatments on d 0 and over the grazing period were managed as single groups by sex in a rotational grazing system. When pasture forage availability became limited, cattle were supplemented with preserved forage but not concentrate supplements. Weight gains by heifers treated with 2IP, 4IP, and 6IP were greater (P < 0.05) than SC heifers but not different from each other. Weight gains by steers treated with 2IP, 4IP, and 6IP were greater than SC steers (P < 0.05), and ADG by steers treated with 6IP was greater (P < 0.05) than steers given 2IP or 4IP. Trial 2 was a multisite grazing study performed with heifers and steers to compare ADG after treatment with one 6-pellet, coated implant delivering 21 mg EB and 150 mg TBA (6IP) to sham treated negative controls (SC) over a grazing period of at least 200 d. A completely random design was used at each site, with the goal to treat 70 cattle per site, treatment, and sex; data were pooled across sites. Heifers (n = 558, initial BW = 229 ± 16 kg) and steers (n = 555, initial BW = 235 ± 20 kg) grazed in rotational programs consistent with regional practices for an average of 202 d. When necessary, cattle were supplemented with preserved forage, but no concentrate supplements were fed. Over 202 d, ADG by heifers treated with 6IP was 11.3% greater (P = 0.0035) than SC heifers (0.64 ± 0.06 kg/d), and ADG by steers treated with 6IP was 17.2% greater (P = 0.0054) than SC steers (0.66 ± 0.08 kg/d). In neither study was there evidence that concurrent therapeutic treatments or abnormal health observations were influenced by experimental treatments. These studies demonstrated that a 6-pellet implant with a polymeric, porous coating that delivers 21 mg EB and 150 mg TBA improved ADG by grazing heifers and steers for at least 200 d compared to sham-implanted negative controls.

Dose confirmation of moxidectin pour-on against natural nematode infections in lactating dairy cows.

The nematocidal effectiveness of moxidectin, administered topically at the rate of 500 mcg/kg BW, was determined for lactating dairy cows. Naturally infected animals were given either topical vehicle or moxidectin (Cydectin Pour-On Fort Dodge Animal Health) at the rate of 1 ml/10 kg BW (10 animals per treatment group), and sacrificed 14-18 days post-treatment for nematode enumeration. 100% efficacies were recorded for Ostertagia lyrata males, Cooperia punctata males and Oesophagostomum radiatum L4, with treatment group differences in geometric means significant (P < 0.05) for all. Populations of Trichostrongylus L4 and adult O. radiatum were also reduced by 100%, but low prevalence rates in the control animals precluded meaningful statistical inference. Nematode populations for which efficacies ranged from 96.7 to 99.6% (based on geometric means) and for which treatment group differences were significant (P < 0.05) included Ostertagia spp. adult females, inhibited L4 and developing L4, O. ostertagi adult males, Trichostrongylus axei adults and Cooperia spp. adult females. For all nematodes combined, moxidectin was 98.9% efficacious. In addition to exhibiting excellent nematocidal effectiveness, topical moxidectin was demonstrated to be safe, with animal health and milk production unaffected during the study.

Endectocidal efficacies of doramectin in naturally parasitized pigs.

The studies reported here were conducted to investigate the effectiveness of doramectin, given intramuscularly at the rate of 300 micrograms kg-1 of bodyweight, in the treatment of naturally acquired porcine nematodosis and acariasis. Twenty pigs demonstrated to be naturally infected with pulmonary and gastrointestinal nematodes were used in one control study, and 22 pigs demonstrated to be naturally parasitized with Sarcoptes scabiei var. suis were used in a second study. In both studies, animals were evenly divided between doramectin plus vehicle and vehicle-treated groups by restricted randomization. In the anthelmintic study, all pigs were necropsied for parasite collection on post-treatment Days 14 and 15. The acaricidal evaluation study was 28 days in duration after treatment, with mite population quantifications on the day of treatment and on post-treatment Days 7, 14, 21 and 28. Doramectin proved 100% effective in the removal of Metastrongylus salmi, M. elongatus, M. pudendotectus, Strongyloides ransomi, Ascaris suum and Oesophagostomum dentatum. Levels of Hyostrongylus rubidus, Ascarops strongylina and Macracanthorhynchus hirudinaceus, as observed at necropsy in the doramectin-treated pigs, were reduced by 99.2%, 99.5% and 62.1%, respectively, as compared with levels seen in the control pigs. In regard to Sarcoptes scabiei var. suis, no live mites were recovered from doramectin-treated pigs during the 7-28 day post-treatment period. In conclusion, doramectin proved highly effective in the treatment of naturally acquired porcine nematodosis and Sarcoptes scabiei var. suis infestation. In addition, all treatments were safe and well tolerated, with no adverse reactions noted in any trial animals.

The effectiveness of a single treatment with doramectin or ivermectin in the control of gastrointestinal nematodes in grazing yearling stocker cattle.

Four studies were conducted to a similar experimental design in the U.S. to evaluate the effectiveness of doramectin injectable administered to yearling stocker cattle in the control of gastrointestinal nematodiasis over the subsequent grazing period. Studies were conducted in Wisconsin (WI) and Arkansas (AR) during the summer season. The other two studies were conducted in Georgia (GA) and Mississippi (MS) during the winter/spring season. Doramectin was compared with both ivermectin injectable and ivermectin pour-on in the WI study, with ivermectin injectable alone in the GA study and with ivermectin pour-on alone in the other two studies. At each study site, an area of permanent pasture previously grazed by parasitized animals was subdivided by fencing into equal pasture units each with its own water supply. A treatment designation (non-medicated control, doramectin injectable, ivermectin injectable or ivermectin pour-on) was randomly assigned to each pasture unit. Weaned beef calves with confirmed gastrointestinal nematode infections were randomly allotted to a pasture unit and corresponding treatment group. Each treatment group consisted of three replicates of seven animals per pasture unit (total 21 animals) in the WI study, three replicates of four or six animals per pasture unit (total 16 animals) in the AR study, five replicates of six animals per pasture unit (total 30 animals) in the GA study and three replicates of 12 animals per pasture unit (total 36 animals) in the MS study. Treatments were 1% doramectin injectable solution, 1% ivermectin injectable solution, 0.5% ivermectin pour-on solution or non-medicated controls. The injectables were administered at a dose of 1 ml/50 kg body weight (200 micrograms doramectin or ivermectin/kg) by subcutaneous injection in the neck. Ivermectin pour-on solution was administered topically at a dose of 1 ml/10 kg body weight (500 micrograms ivermectin/kg). After receiving their prescribed treatment, animals were placed on their designated pasture unit where they remained for the entire grazing period (84-140 days). Fecal nematode egg counts and body weights were monitored at predetermined intervals throughout each study. Doramectin treatment reduced pretreatment egg counts by between 95 and 100% by 21 days post-treatment. Subsequent rises in egg output from exposure to infective pastures were delayed by two to four weeks resulting in substantial reductions in total egg deposition over the grazing period and, therefore, potential pasture recontamination. Doramectin treatment resulted in substantial average daily weight gain advantages (0.152-0.272 kg) over the grazing season compared to non-medicated controls. Advantages were statistically significant (P < 0.05) in three of the four studies. There were no significant differences (P > 0.05) in average daily gain between the doramectin and ivermectin injectable or ivermectin pour-on treated groups.

World Association for the Advancement of Veterinary Parasitology (WAAVP) guidelines for evaluating the effectiveness of anthelmintics in chickens and turkeys.

These guidelines have been prepared to assist in the planning, operation and interpretation of studies designed to assess the effectiveness of drugs against helminth parasites of chickens and turkeys. They are the first to be compiled under the auspices of the World Association for the Advancement of Veterinary Parasitology (WAAVP) for these parasites. The advantages and disadvantages of the widely used critical and controlled tests are discussed. Information is provided on the selection of animals for experiments, animal housing, feed, dose determination studies, confirmatory and field trials, record keeping and necropsy procedures. This document should help investigators and those involved in product approval and registration in conducting and evaluating studies concerned with determining the effectiveness and safety of anthelmintic drugs.

Effects of subcutaneous injections of a long acting moxidectin formulation in grazing beef cattle on parasite fecal egg reduction and animal weight gain.

Trials were conducted in Arkansas, Idaho, Illinois and Wisconsin using a common protocol to evaluate effectiveness and safety of a long acting (LA), oil-based injectable formulation of moxidectin in beef cattle grazing spring and/or summer pastures. At each site, 150 cattle (steers and/or heifers) were blocked based on pretreatment fecal strongyle egg counts (EPG) and then randomly assigned to treatments within blocks. Presence of naturally acquired parasitic infections, confirmed by presence of parasite eggs in feces, was a prerequisite for study enrollment. Within each block of three animals, two received moxidectin LA injectable on day 0 at a dosing rate of 1.0 mg moxidectin/kg b.w. into the dorsal aspect of the proximal third of the ear, and one received a placebo control treatment. Cattle were weighed before treatment and on day 55 or 56 (55/56) after treatment. Fecal samples were also collected from 10 randomly selected blocks of animals at each site on days 14, 28 and 55/56 for EPG quantification. Average daily gain (ADG) was computed over the posttreatment period. Data pertaining to ADG and EPG were combined across sites and analyzed by mixed model analysis of variance to assess the fixed effect of treatment and random effects of site, block within site and the treatment by site interaction. Compared to placebo-treated controls, the geometric means of fecal EPG counts from cattle treated with moxidectin LA injectable were reduced 99.8% 14 days after treatment, 99.1% 28 days after treatment and 96.7% 55/56 days after treatment. Rate of weight gain by cattle treated with moxidectin LA injectable was 0.59 kg/day, or 23% (0.11 kg/day) more than placebo-treated controls (P<0.05). None of the cattle treated with moxidectin LA injectable exhibited signs of macrocyclic lactone toxicosis. Summarized across all study sites, proportions of cattle that received concurrent therapeutic treatments were similar among treatment groups. Study results demonstrate that moxidectin cattle LA injectable administered at a dosing rate of 1.0 mg moxidectin/kg b.w. to grazing beef cattle was effective and safe.

Studies on the effect of concurrent infections of Ascaridia dissimilis and Eimeria meleagrimitis in turkeys.

The effects of concurrent infections of Ascaridia dissimilis and Eimeria meleagrimitis in turkeys were studied in two separate trials. In the first trial, newly larvated ova were used to inoculate poults 7 or 3 days before, on the same day as, or 3 days after the poults received E. meleagrimitis. Poults receiving the A. dissimilis 3 days before, on the same day as, or 3 days after receiving E. meleagrimitis had significantly lower total oocyst production than the E. meleagrimitis-positive control. In the second trial, larvated ova that were approximately 100 days old were used in the same regimen. In this trial, poults that were inoculated with A. dissimilis 3 days before or 3 days after receiving the E. meleagrimitis produced significantly fewer oocysts than poults inoculated simultaneously with both parasites. Poults inoculated with A. dissimilis 3 days before receiving E. meleagrimitis also had significantly fewer third-stage nematodes than the A. dissimilis-positive controls. There were no significant differences in weight gain between treatments in either trial.

A survey into the prevalence of poultry helminths in northwest Arkansas commercial broiler chickens.

A 12-month survey was conducted to determine the prevalence of poultry helminths in Northwest Arkansas commercial broiler chickens. Intestinal tracts from market-ready broilers were collected weekly from two commercial broiler companies; a total of 3542 intestinal tracts were collected for parasite enumeration from 67 company A and 52 company B farms. Ascaridia galli was found on 37.3% of company A farms and 3.9% of company B farms, Raillietina cesticillus was found on 67.2% of company A farms and 69.2% of company B farms, and Heterakis gallinarum was found on 7.5% of company A farms and 1.9% of company B farms. No other parasitic helminths were found. No significant relationship was detected between grow-out feed efficiency and helminth infection rate or magnitude.

Dose-titration of fenbendazole in the treatment of poultry nematodiasis.

Broiler chickens were fed ad libitum diets containing fenbendazole at various concentrations and durations for the removal of adult Ascaridia galli, Heterakis gallinarum, and Capillaria obsignata. All regimens were 100% effective against A. galli. Fenbendazole at doses of 80 ppm for 3 days and 48 or 30 ppm for 5 days was 100% effective against H. gallinarum. C. obsignata was not removed completely by any regimen, but greater than or equal to 95% effectiveness was seen in birds given fenbendazole at doses of 80 ppm for 3 days and 48 ppm for 5 days. All medicated rations were readily consumed, and the treated birds exhibited no adverse reactions.

Subclinical effects and fenbendazole treatment of turkey ascaridiasis under simulated field conditions.

Under simulated natural conditions of bird production and parasite challenge, the effects of ascaridiasis and the effectiveness of fenbendazole treatment (6-day regimes in the feed at 16 ppm) were documented. Birds were artificially challenged with ascarid larvae on a daily basis from day 35 to 112, with bird grow out ending on day 119. Experimental groups, on a per pen basis, were infected control, treated with fenbendazole at days 63-69, treated with fenbendazole at days 63-69 and days 91-97, and uninfected control. In the same order as above, and on an experimental group mean bird basis, final weights were 13.34, 13.47, 13.59, and 13.78 kg, average daily gains from day 7 to day 119 were 117.8, 118.9, 120.1, and 121.8 g, and units gained per unit of feed consumed from day 7 to day 119 were 0.337, 0.341, 0.347, and 0.362. Infected control bird mean Ascaridia dissimilis burdens, with all stages combined, ranged from 351.1 on day 63 to 117.2 on day 91, levels seen commonly with naturally infected commercial turkeys. Trial data dearly indicated that moderate A. dissimilis burdens negatively impacted animal performance (average daily gains and feed efficiencies) and that these parasite burdens are effectively removed by fenbendazole treatment.

Haemonchus contortus resistance in straightbred and crossbred Barbados Blackbelly sheep.

Resistance to Haemonchus contortus infection was studied in two experiments conducted with 52 lambs of widely different genetic background. Breed groups compared were: Dorset (D), Barbados Blackbelly (B), Dorset x Blackbelly (D x B), Suffolk x Blackbelly (S x B), Suffolk x Dorset x Blackbelly (S x D x B,[1/4 B]) and nonBlackbelly (NB, D and S). In each experiment, lambs were raised on concrete from birth and were essentially parasite free until infective larvae were administered. In Exp. 1, D x B, S x D x B and D wether lambs approximately 3 months old were infected with a standard dose of invective larvae estimated to be 98% H. contortus. D x B lambs had a longer (P < .05) prepatency period and, at necropsy 17-day postinfection, had a higher (P < .05) percentage of female parasites classified as immature than did the other breed groups. These data showed that the development of H. contortus larvae was inhibited in D x B host animals. In Exp. 2, B, D x B, S x B and NB ewe and wether lambs approximately 4 months old were treated with three sensitizing doses of H. contortus larvae. These were followed by a challenge infection. On the basis of fecal egg counts (eggs per gram feces, EPG), there was no evidence that the challenge infection induced a self-cure reaction in any breed group. All lambs with B breeding had significantly higher Hb levels at the end of the experiment than did NB lambs. b and S x B lambs had higher (P < .05) Hb levels than the D x B lambs, and B lambs had the highest (P < .05) mean corpuscular hemoglobin concentrations. Five days after the challenge infection, B, D x B and S x B lambs also had significantly higher white blood cell levels than did NB lambs. Significant sex differences were also observed in Exp. 2. Ewe lambs had lower final EPG levels, higher preinfection and postinfection Hb levels and higher maximum postinfection cosinophil levels. Breed x sex interactions for these parameters were not significant.

Use of febantel or ivermectin for treatment of calves with experimentally induced Bunostomum phlebotomum infection.

In the first of 2 separate trials, the efficacy of febantel, given at a dosage of 5 mg/kg of body weight, was assessed in calves with 60-day experimentally induced Bunostomum phlebotomum infection. Ten calves were given febantel paste, and 10 were given the vehicle only. All 20 calves were necropsied 7 days after cessation of treatment. Compared with untreated calves, febantel-treated calves harbored 99.4% fewer nematodes. In the second trial, the efficacy of ivermectin, given as a paste formulation at a dosage of 0.2 mg/kg, was assessed in calves with experimentally induced B phlebotomum infection. Ivermectin was given at 18 (n = 6) and 60 (n = 6) days after infection. At each treatment date, 3 additional calves were given vehicle only. At 67 days after infection, all calves were euthanatized. Efficacies of ivermectin against 18- and 60-day infections were 100 and 99.8%, respectively. Both anthelmintic preparations were easily administered, and adverse reactions were not observed.

Survey of helminth infections in Maine dairy cattle.

The survey was done to determine the incidence and seasonal prevalence of the gastrointestinal helminths infecting Maine dairy cattle. Approximately equal groups of calves, heifers, and cows from 13 dairy farms, managerially and geographically representative of dairying in the state, were sampled at regular 2-month intervals over the period of a year. On the basis of fecal egg counts and identification of cultured larvae, the following results were obtained: Of the 94 adult cows, 78 heifers, and 91 calves sampled continuously in the course of the survey, 95.7%, 98.7%, and 96.7%, respectively, were strongylorid positive (infected with Ostertagia, Cooperia, Trichostrongylus, Haemonchus, and Oesophagostomun), with an overall incidence of 97%. Strongyloides papillosus eggs were in 64.6% of the cattle, Bunostomum in 40.3%, Nematodirus in 27.8%, Trichuris in 27.0%, Capillaria in 9.5%, Moniezia in 25.1%, and Dictyocaulus viviparus larvae in 2.7%. Worm burdens, as reflected by mean nematode egg production per gram of feces, varied. The greatest worm burdens were in the calves, followed by the heifers and the cows. A marked variation in egg production related to season was observed, particularly with the strongylorid worms. Peak strongylorid egg production was observed in the May-June sampling period. After the peak period, worm burdens decreased in all groups of cattle to their lowest point during the winter period of January-February. This pattern of egg production was similar to that reported by workers in other parts of the world. Farm management practices were shown to be related to the degree of parasitism existing in these herds. Those herds classed as poorly managed had significantly higher levels of parasitism in young animals than those classed as having fair or good management.

Effectiveness of doramectin for treatment of experimentally induced gastrointestinal tract larval nematode infections in calves.

Anthelmintic efficacy of doramectin, a macrocyclic lactone of the avermectin family, was evaluated against larval parasitic nematodes in calves. The investigational product was given SC at a dosage of 0.2 mg/kg of body weight to 10 calves infected 6 days previously with third-stage larvae of the genera Haemonchus, Ostertagia, Cooperia, and Nematodirus. Ten additional calves with identical larval exposure were given saline solution SC also at 6 days after inoculation, and served as the nonmedicated controls. At 14 or 15 days after treatment, the calves were slaughtered in complete replicate for nematode recovery and subsequent quantifications. In comparing nematode numbers at necropsy for the saline- and doramectin-treated groups, nematocidal effectiveness as directed against fourth-stage larvae was: 100% for Haemonchus placei and Cooperia spp, > 99% for Ostertagia ostertagi, and 64.5% for Nematodirus helvetianus. All treatments were easily administered, and adverse behavioral or tissue reactions were not seen to result from doramectin administration.