Ectonucleotidase and adenosine deaminase as inflammatory marker in dairy cows naturally infected by Dictyocaulus viviparus.

The aim of this study was to evaluate the influence of dictyocaulosis (mild or severe) on enzymes of NTPDase, 5'-nucleotidase, and adenosine deaminase (ADA) of dairy cows naturally infected by Dictyocaulus viviparus. Blood and faeces were collected from 22 dairy cows of the same farm to evaluate NTPDase (ATP and ADP substrate), 5'-nucleotidase, and ADA activities on days 0 (pre-treatment) and 10 (post-treatment). Seric activities of NTPDase (ATP substrate), 5'-nucleotidase, and ADA were lower (P<0.05) in D. viviparus infected animals compared to uninfected cows. The number of D. viviparus larvae per gram of faeces varied among the animals, and they showed different degrees of severity according to respiratory clinical signs of the disease (cough and nasal discharge). Later, these cows were divided into two groups: those with mild (n=10) and severe (n=12) disease. Cows with severe disease showed higher NTPDase activity (ATP substrate) than those with mild disease (P≤0.05). The opposite occurred with NTPDase (ADP substrate), 5'-nucleotidase, and ADA in cows with severe disease, that is, the enzymatic activity of these seric enzymes significantly decreased (P≤0.05) compared to animals with mild disease. Infected animals showed reduced NTPDase activity (ATP and ADP substrate) after treatment. No enzymatic changes were observed for 5'-nucleotidase, and ADA pre- and post-treatment (P>0.05). Based on these results, we conclude that dictyocaulosis alters NTPDase, 5'-nucleotidase, and ADA activities of cow naturally infected by the parasite, in consequence the enzymes act as inflammatory markers.

[(IMPACT OF LUNGWORM INFESTATION ON THE BIOCHEMICAL PARAMETERS OF ANIMALS DURING COMBINATION TREATMENT WITH ALBENDAZOLE AND T- AND B-ACTIVIN)].

Lungworm infection is caused by a Dictyocaulus filaria nematode parasitizing the bronchi and bronchioles of sheep and goats. Various anthelmintics, including albendazole, levamisole, fenbendazole, ivermectins, and others, are used to treat the animals. The aim of this investigation was to study the impact of lungworm infestation on the biochemical parameters of animals during combination treatment with albendazole and T- and B-activin. Experiments were carried out in 20 uninfected mongrel lambs aged 4-5 months. Infectious D.filaria larvae were given with water to 15 lambs once orally at a dose of 1000 larvae per head. 5 uninfected lambs served as a control group. The time course of changes in serum bio- chemical parameters was studied in animals. Treatment with Albena in combination with T- and B-activin in lambs ex- perimentally infested with lungworm was found to restore their biochemical reactivity. After sheep treatment with Albena alone, biochemical parameters were noted to tend to normalize, but their normal full recovery did not take place.

Efficacy of eprinomectin pour-on treatment in sheep naturally infected with Dictyocaulus filaria and Cystocaulus ocreatus.

The efficacy of eprinomectin on Dictyocaulus filaria and Cystocaulus ocreatus in naturally infected sheep was evaluated in the present study. In total, 30 infected sheep were randomly divided into two groups: treated (n = 15) and untreated (n = 15). A single pour-on dose of eprinomectin (0.5 mg/kg) was administered to the treated group. No medication was used in the untreated group. Faecal larval counts were performed on pre-treatment (day 0) and post-treatment (days 7, 14, 21 and 42) days. Eprinomectin was found to be 100% effective against D. filaria on day 7 post-treatment when compared with the untreated group and it maintained this effect on days 14, 21 and 42. However, the decrease in faecal larval count of C. ocreatus was found to be 86, 86 and 91%, on days 14, 21 and 42, respectively.

Efficacy of eprinomectin pour-on against Dictyocaulus arnfieldi infection in donkeys (Equus asinus).

A trial to assess the efficacy of eprinomectin (EPM) against the lungworm Dictyocaulus arnfieldi was carried out on 15, naturally-infected donkeys. Ten animals were treated with a 'pour-on' EPM preparation (at a dose of 0.5 mg/kg bodyweight), and five animals acted as controls. Faecal larval counts were carried out two days before treatment, on day of treatment and 7, 14, 21 and 28 days post-treatment with the anthelmintic. EPM was 100% effective in eliminating faecal larvae from day 7, until the end of study at day 28. No adverse drug-reactions or side-effects were observed in any of the treated donkeys.

Deep insights into Dictyocaulus viviparus transcriptomes provides unique prospects for new drug targets and disease intervention.

The lungworm, Dictyocaulus viviparus, causes parasitic bronchitis in cattle, and is responsible for substantial economic losses in temperate regions of the world. Here, we undertake the first large-scale exploration of available transcriptomic data for this lungworm, examine differences in transcription between different stages/both genders and identify and prioritize essential molecules linked to fundamental metabolic pathways, which could represent novel drug targets. Approximately 3 million expressed sequence tags (ESTs), generated by 454 sequencing from third-stage larvae (L3s) as well as adult females and males of D. viviparus, were assembled and annotated. The assembly of these sequences yielded ~61,000 contigs, of which relatively large proportions encoded collagens (4.3%), ubiquitins (2.1%) and serine/threonine protein kinases (1.9%). Subtractive analysis in silico identified 6928 nucleotide sequences as being uniquely transcribed in L3, and 5203 and 7889 transcripts as being exclusive to the adult female and male, respectively. Most peptides predicted from the conceptual translations were nucleoplasmins (L3), serine/threonine protein kinases (female) and major sperm proteins (male). Additional analyses allowed the prediction of three drug target candidates, whose Caenorhabditis elegans homologues were linked to a lethal RNA interference phenotype. This detailed exploration, combined with future transcriptomic sequencing of all developmental stages of D. viviparus, will facilitate future investigations of the molecular biology of this parasitic nematode as well as genomic sequencing. These advances will underpin the discovery of new drug and/or vaccine targets, focused on biotechnological outcomes.

An outbreak of dictyocaulosis in lactating cows on a dairy farm.

CASE DESCRIPTION: The owner of a herd of 74 Holstein-Friesian cattle reported decreased milk production, weight loss, and coughing among lactating cows. Owner-initiated antimicrobial treatment was unsuccessful; 1 lactating cow died, and 50% of the lactating cows had clinical signs of respiratory distress, such as tachypnea and coughing. CLINICAL FINDINGS: On the basis of history, physical examination findings, and fecal examination results, affected animals were determined to have Dictyocaulus viviparus (lungworm) infestation. The disease history suggested that the herd contained cows with subclinical patent lungworm infestations; after introduction of susceptible heifers, the pastures had become heavily infested with D viviparus and clinical problems subsequently developed in both newly introduced and resident cows. TREATMENT AND OUTCOME: Affected and unaffected heifers and adult cows were treated with a pour-on formulation of eprinomectin (0.5 mg/kg [0.23 mg/lb]). One animal died, but 2 weeks after treatment, clinical signs among affected cattle were markedly improved. Ten weeks after treatment, milk production improved from 23 kg/cow/d (51 lb/cow/d) to 28 kg/cow/d (62 lb/cow/d). CLINICAL RELEVANCE: The outbreak provides additional evidence that dictyocaulosis is becoming more common among adult dairy cattle, rather than almost exclusively affecting young stock. This may be attributable to anthelmintic use and management practices on dairy farms. Combined with anecdotal reports of an increase in the incidence of dictyocaulosis among adult cattle in North America, D viviparus infestation should be included as a differential diagnosis for decreased milk production, weight loss, and coughing among adult dairy cattle.

Lungworms of ruminants.

Several species of nematodes parasitize the respiratory tract of ruminants. Disease due to infection with these parasites occurs less frequently in North America than in other parts of the world but can be locally and regionally important. The life cycles, epidemiology, pathology, diagnosis and treatment of Dictyocaulus viviparus, Dictyocaulus filaria, and Muellerius capillaris are summarized in this article.

Suppressive treatment of abamectin against Dictyocaulus viviparus and the occurrence of resistance in first-grazing-season calves.

Dictyocaulus viviparus cause severe lung infections and are endemic in some areas of temperate and tropical countries. Treatment is based on strategic nematode control programs using potent compounds with no reports of drug failure. Macrocyclic lactones (MLs) are available at different concentrations and combinations and have being used heavily by producers. The objective of this work was to determine the efficacy of the MLs ivermectin, moxidectin, doramectin, and abamectin, and the combination ivermectin plus abamectin in naturally infected calves (n=70). Initial infection was determined by necropsy of tracer animals. Faecal larval counts determined that none of the compounds used was able to eliminate D. viviparus for up to 28 days after treatment. The "Area Nova" strain was isolated for future work.

Targeted selective treatment of lungworm infection in an organic dairy herd in Sweden.

The effect of targeted selective anthelmintic treatment on the seroprevalence of the lungworm Dictyocaulus viviparus in cattle was investigated. The study was commenced on an organic dairy enterprise in Sweden in November 1998 after the observation of an outbreak dictyocaulosis in the herd, and then continued for almost 3 years. The first year sampling was conducted on a monthly basis and then biannually with the exception of between August and November 2000 when sampling was performed monthly following a second outbreak of dictyocaulosis. Throughout the study, blood samples were examined for specific IgG(1) levels from all animals in the herd that had been grazing for more than 3 months. At the first sampling occasion, 13% out of the 90 blood samples were seropositive. One month later, after targeted selective treatment with eprinomectin (Eprinex), Merial), the whole herd was seronegative. Seroprevalence then gradually increased and 1 year later it returned to levels similar to those observed at the start of the study. At turnout in April 2000, seroprevalence was 1.3% but it then rapidly increased to 28% and 30% in August and September, respectively. This increase was mainly due to an increase in FSG animals of which many were coughing. Consequently, all seropositive animals were injected with ivermectin (Ivomec), Merial) at 0.05 mg/kg body weight in late August 2000. Although all animals recovered, seroprevalence was only reduced to 12% 1 month later. The differences in seroprevalence after both of these anthelmintic treatments were probably attributed to the timing. The first deworming with eprinomectin was conducted in November when the infection already was transient, whereas ivermectin in connection with the second outbreak was injected in a more acute phase of the infection cycle. Infection levels in 2001 were low with seroprevalences of 2.3% and 5.6% in May and September, respectively. These results show that dictyocaulosis in Sweden can be effectively controlled by the use of macrocyclic lactones. However, the infection was not eradicated from the herd despite close monitoring of the seroprevalence and targeted selective treatment of every seropositive animal on two occasions.

Preventive vaccination of lactating and pregnant heifers against lungworm: safety and protection in three dairy herds.

A study of the safety of a vaccine against lungworm was carried out with pregnant and lactating heifers from three dairy herds with a previous history of lungworm outbreaks in adult cows. Half of the heifers were vaccinated while the other half were not. A slight temporary cough following the vaccination was only observed in one herd. No adverse effects on pregnancy or milk production were seen. All heifers were serologically and coprologically examined before the first, before and after the second immunization, 3 months after introduction to pasture and at the end of the grazing season. Serological and faecal examination of the dairy cows before introduction into pasture confirmed the presence of at least one Dictyocaulus viviparus carrier in each herd. Lungworm infection occurred in all herds during the grazing season, most prominently in the herd with the highest number of heifers. In this herd, mild coughing associated with the lungworm infection was noticed, especially in the non vaccinated heifers. No other signs or symptoms were observed. It is concluded that a vaccine against D. viviparus can be used safely in heifers, before they are introduced into the adult herd, and that this vaccine can be used as a preventive measure against lungworm outbreaks in adult cattle.

The effect of treatment with eprinomectin on lungworms at early patency on the development of immunity in young cattle.

An experiment was carried out to study the effect of topical application of eprinomectin at early patency on the build up of infection and development of protection against Dictyocaulus viviparus in young cattle. Three groups of six calves were used and parasitological and blood variables were monitored at weekly intervals throughout the trial. At the start of the experiment calves in groups A and B were experimentally inoculated with 100 D. viviparus infective third-stage larvae (L3) for five consecutive days, whereas calves in group C served as uninfected controls. The calves in group A were each treated with eprinomectin (0.5mg/kg bodyweight) in a pour-on formulation at early patency at day 24 post the first inoculation, whereas the calves in groups B and C were left untreated. Seven weeks following anthelmintic treatment all groups were challenged with 1500 L3. Another 4 weeks later the animals were sacrificed and established worms in the lungs were counted. Moderate transient signs of lungworm disease occurred both in groups A and B. However, group B calves were found to be about 8 times more resistant than those in group A, whereas the naive infection controls in Group C was found to be about 35 times more susceptible to infection. Also the ELISA values showed that the course of infection was different between experimental groups. The eosinophil counts prior to and at the time of slaughter indicate that immunity was involved in the protection and the response was correlated with previous exposure and worm load. Weight gains differed significantly, but only between groups A and C and between groups B and C that on an average were approximately 13kg heavier at the termination of the experiment. It was concluded that eprinomectin was effective against established adult lungworms. However, the untreated calves (group B) developed a more marked resistance to lungworms compared to those that were subjected to anthelmintic treatment at early patency (group A). On the other hand, the cumulative number of excreted larvae was on an average 43 times higher in group B as compared to group A. Consequently, infected calves that remain out on pasture should be treated. This will restrain transmission of the parasite despite the fact that immunity is deteriorated.

Efficacy of moxidectin 1% injectable and 0.2% oral drench against natural infection by Dictyocaulus filaria in sheep.

Two separate trials (I and II) with 34 and 32 Churra ewes, respectively, and distributed into two groups, have been carried out to evaluate the efficacy of two different formulations of moxidectin at a dose rate of 0.2mg/kg body weight (b.w.) against natural infection by Dictyocaulus filaria in sheep. Trial I was designed to evaluate a 1% moxidectin injectable formulation, whereas in trial II a 0.2% moxidectin oral drench formulation was used. The efficacy was measured on the basis of the reduction of the faecal larval counts and of adult worm recoveries at slaughter. In each trial, a group of animals was treated on day 0 with moxidectin 1% injectable or moxidectin 0.2% oral drench and the other group acted as untreated control. When the faecal larval counts was compared within the treated groups, the efficacy was over 95% until day +13, and 100% at the remainder of the sampling dates after the application of injectable moxidectin, whereas in trial II, the larvae per gram (lpg) of faeces increased until the first sampling time post treatment (p.t.), day +6, and zero counts were recorded for all animals by the following days. On the basis of adult worm recoveries at necropsy, the efficacy of the treatment was 100% in both trials, however, adult worms were detected at slaughter for all control sheep. These results indicate that moxidectin 1% injectable and moxidectin 0.2% oral drench, administered at 0.2mg/kg b.w., were 100% effective against D. filaria infection in sheep. No adverse reactions to the treatments were observed in the animals.

Treatment vs non-treatment of helminth infections in cattle: defining the threshold.

Helminth infections are an important cause of lost productivity in livestock world-wide, often necessitating anthelmintic treatment. However, a large part of the anthelmintics are used indiscriminately because the parasite levels are too low to justify treatment or because the treatments are not correctly programmed, resulting in undertreatment or overtreatment. The objective of this paper is to discuss possible thresholds for anthelmintic treatment of some of the more important helminth infections in livestock, i.e. gastrointestinal nematodes, lungworms and liver fluke, to promote a more appropriate use of anthelmintics. When possible, a distinction is made between therapeutic thresholds, production-based thresholds and preventive thresholds. A "therapeutic threshold" is intended to identify (an) animal(s) with parasite levels that necessitate immediate treatment. The therapeutic threshold is basically the diagnosis of clinical disease, and can be determined relatively easily for the parasites discussed in this paper. A "production-based threshold" is intended to measure the effects of sub-clinical parasitism on productivity parameters, such as weight gain and milk yield, before clinical disease occurs. Finally, a "preventive threshold" is meant to predict future infection levels, to enable the application of appropriate control measures.

Patterns of parasitic nematode infection and immunity in dairy heifers treated with ivermectin in a sustained-release bolus formulation either at turnout or in the middle of the grazing season.

Twenty-eight Holstein-Friesian heifers, born the previous year and weighing between 130 and 310 kg, were allocated to one of two treatment groups by restricted randomisation, based on their initial weight. The heifers in group 1 were each treated with ivermectin in a sustained-release bolus formulation at turnout in April, and those in group 2 were each given an ivermectin bolus on July 10, 84 days after turnout. On that day the mean geometric worm egg counts of groups 1 and 2 were 0.4/g and 38.8/g, respectively, and they both had a mean plasma pepsinogen concentration of 0.59 iu/litre; in group 1, two of 14 faecal samples were positive for Dictyocaulus viviparus larvae, and in group 2 all 13 samples were positive; in group 1 eight calves were positive and three inconclusive for the presence of antibodies to D viviparus, and in group 2 the corresponding figures were 10 positive and two inconclusive; the mean liveweights of groups 1 and 2 were 274.4 kg and 262.8 kg, respectively. By December 4,231 days after turnout, the corresponding results were: mean geometric worm egg counts of 2.2/g and 0.5/g; one of 13 and none of 14 faecal samples positive for D viviparus larvae; 12 positive and two inconclusive and none positive and 10 inconclusive for the presence of antibodies to D viviparus; 214 days after turnout their mean liveweights were 361.1 kg and 358.3 kg. Although the patterns of parasitic nematode infection were different in the two groups during the grazing season, by the time they were housed both groups had achieved similar liveweights and showed evidence of an immune response to both D viviparus and gastrointestinal nematodes.

Effect of condensed tannins extracted from four forages on the viability of the larvae of deer lungworms and gastrointestinal nematodes.

The inhibitory activity of condensed tannins extracted from four forage legume plants were evaluated by using a larval migration inhibition assay. The first (L1) and third (L3) stages of deer lungworm (Dictyocaulus viviparus), and the third stage (L3) of deer gastrointestinal nematodes were incubated with tannins extracted from Lotus pedunculatus, Lotus corniculatus, sulla (Hedysarum coronarium) and sainfoin (Onobrychus viciifolia). The tannins extracted from all the forages had inhibitory activity as measured by their ability to paralyse the larvae and inhibit them from passing through sieves. At the highest concentration used (1200 microg/ml) the tannins extracted from sainfoin had the highest activity against ensheathed L1 lungworm larvae (58 per cent), followed by L. pedunculatus (45 per cent), sulla (42 per cent) and L. comiculatus (35 per cent) when the larvae were incubated at 37 degrees C. The same trend, but with lower activities, was observed when the larvae were incubated at 22 degrees C. Anthelmintic activity against L3 lungworm larvae was evaluated by measuring the death rate of ensheathed L3 larvae after incubation with condensed tannins for two, 24 and 48 hours at room temperature (22 degrees C). The death rate was significantly higher (P<0.001) after 48 hours incubation than after two hours or 24 hours, and significantly higher (P<0.001) after 24 hours than after two hours incubation. Condensed tannins from sainfoin had the highest inhibitory activity followed by L. pedunculatus, sulla and L. comiculatus. The tannins from sainfoin also had the highest activity against L3 larvae of gastrointestinal nematodes, followed by L. pedunculatus, sulla and L. comiculatus. Exsheathed larvae of gastrointestinal nematodes were significantly more susceptible to the action of the tannins than ensheathed larvae.

Induction of protective immunity to Dictyocaulus viviparus in calves while under treatment with endectocides.

Three groups of five parasite-naive calves were used. The treatments were: (a) Group 1 calves were weighed on Day 0 and injected with doramectin at 200 microg/kg. From Day 1 to 19 they were dosed orally with 2000 infective larvae of Dictyocaulus viviparus. On Day 28 they were again injected with doramectin, and infected with D. viviparus larvae from Days 33 to 41. They were then left untreated until Day 81 when they were infected with 20 infective larvae of D. viviparus per kg body weight. They were killed on Day 110 and lungworms were counted; (b) Group 2 calves were immunised with oral lungworm vaccine on Days 0 and 28, and infected and slaughtered as Group 1 on Days 81 and 110, respectively; (c) Group 3 calves acted as infection controls. Blood samples were taken at Days 0, 21, 49, 77 and 110 for antibody tests to D. viviparus. At autopsy there were no significant differences between the number of lungworms from Groups 1 and 2 (Means 17.4 and 31.3, respectively); Group 1 had significantly less value than Group 3 (Mean 228) (p < 0.05). Increased antibody titres to the larval sheath of the infective larvae were observed from Groups 1 and 2, showing that the larvae in Group 1 had penetrated the intestine before being killed by the circulating anthelmintic. This experiment shows that if calves are exposed to infective larvae while under systemic endectocide cover, an immune reaction is stimulated.

Persistent efficacy of doramectin injectable against artificially induced infections with Cooperia punctata and Dictyocaulus viviparus in cattle.

Three studies were conducted to evaluate the persistent efficacy of doramectin injectable solution against experimental challenges with infective larvae of Cooperia punctata and Dictyocaulus viviparus. In each study, four groups of ten randomly-assigned calves, negative for trichostrongyle-type eggs on fecal examination, were treated subcutaneously in the midline of the neck with saline (1 ml/50 kg) on Day 0 or doramectin (200 microg/kg = 1 ml/50 kg) on Day 0, 7, or 14. Two additional calves from the same pool of animals were randomly assigned as larval-viability monitors and received no treatment. On Days 14-28, approximately 1000 and 50 infective larvae of Cooperia spp. and D. viviparus, respectively, were administered daily by gavage to each animal in Groups T1-T4. On Day 28, the two larval-viability monitor calves were inoculated in a similar manner with a single dose of approximately 30000 and 2000 larvae of Cooperia spp. and D. viviparus, respectively. Equal numbers of calves from each treatment group were killed on Days 42-45, as well as the two viability monitor animals to enumerate worm numbers. A 2% or 5% aliquot of small intestinal contents and washings were examined for worm quantification and identification, while 100% of the lung recoveries were quantified and identified. For each study and across the three studies, geometric mean worm recoveries for each treatment group were calculated from the natural log transformed data (worm count + 1) and were used to estimate percentage reduction. In the three studies, doramectin injectable solution was 97.5% efficacious against lungworms for up to 28 days and was 99.8% efficacious in reducing infection resulting from challenge with infective larvae of C. punctata for at least 28 days post-treatment.

Efficacy of topically administered doramectin against eyeworms, lungworms, and gastrointestinal nematodes of cattle.

OBJECTIVE: To evaluate efficacy of topically administered doramectin against eyeworms, lungworms, and gastrointestinal nematodes of cattle. ANIMALS: 400 cattle (20 cattle in each of 20 trials). PROCEDURE: Trials were conducted in North America; natural and experimentally induced infections were used. In each trial, cattle were allocated randomly to control (placebo [saline [0.9% NaCl] solution at 1 ml/10 kg of body weight] or untreated; n = 10) or doramectin-treated (500 microg/kg of body weight; 10) groups. Treatments were applied in a single passage along the midline of the back, from the withers to the tailhead. Cattle were euthanatized > or =14 days after treatment, and worm burdens were determined by use of standard techniques. RESULTS: Efficacy of doramectin was > or =95.3% against adults of Thelazia gulosa, T skrjabini, Dictyocaulus viviparus, Haemonchus contortus, H placei, Ostertagia lyrata, O ostertagi, Trichostrongylus axei, Bunostomum phlebotomum, Capillaria spp, Cooperia oncophora, C pectinata, C punctata, C spatulata, C surnabada, Nematodirus spathiger, Strongyloides papillosus, T colubriformis, Oesophagostomum radiatum, and Trichuris spp. Efficacy was 95.1% against fourth-stage larvae of D viviparus, H placei, O lyrata, O ostertagi, T axei, C oncophora, C punctata, C spatulata, C surnabada, N helvetianus, T colubriformis, O radiatum, and Trichuris spp. In addition, efficacy against inhibited fourth-stage larvae of O ostertagi and Ostertagia spp was > or =98.1%. CONCLUSIONS AND CLINICAL RELEVANCE: A single topical application of doramectin pour-on was efficacious against a broad range of nematode species in cattle.

Comparison of the persistent efficacy of the injectable and pour-on formulations of doramectin against artificially-induced infection with Dictyocaulus viviparus in cattle.

The persistent efficacy of the injectable and topical formulations of doramectin was compared against experimental challenges with infective larvae of Dictyocaulus viviparus in two separate studies. Four groups of 10 randomly-assigned calves, negative for lungworm larvae by the Baermann technique, were used in each study. Calves were treated subcutaneously in the midline of the neck or poured down the midline of the back with saline (1 ml/50 kg. injection: 1 ml/10 kg. pour-on) on Day 0 or doramectin (200 microg/kg = 1 ml/50 kg. injection: 500 microg/kg = 1 ml/10 kg. pour-on) on Day 0, 7, or 14. Two additional calves from the same pool of animals were randomly assigned as larval-viability monitors and received no treatment. Calves were inoculated daily with a gavage of approximately 100 larvae of D. viviparus from days 35 to 49 for the injectable study and days 28 to 42 for the pour-on study. The two larval viability monitor calves received approximately 3000 infective larvae in the same manner on Day 49 or 42 for the injectable and pour-on studies, respectively. Equal numbers of calves from each treatment group as well as the larval viability monitor calves were necropsied on days 14 and 15 after the last lungworm inoculation to enumerate the worm burden. The worms recovered were quantified and identified. For each study, geometric mean worm recoveries for each treatment group were back transformed from the natural log-transformed data (worm count +1) and were used to estimate percentage reduction. Doramectin injectable solution was 100.0% efficacious against lungworms for up to 49 days and the pour-on formulation was 100.0%, 93.1% and 81.5% effective in reducing lungworm infection resulting from challenge infection for up to 28, 35, and 42 days post-treatment, respectively.