Delay in timing of the oxfendazole pulse release bolus in calves in the Netherlands

Summary

The efficacy of the oxfendazole pulse release bolus (OPRB) was tested in a grazing experiment at the University of Utrecht. Three groups of four OPRB‐treated calves and one group of four untreated control calves were grazed on separate pastures between 18 May and 21 October 1987. Based on faecal egg counts for strongyle‐type eggs and Nematodirus eggs, embryonation of Nematodirus eggs and faecal larval counts for lungworm, the first pulse of oxfendazole was released after 28 to 63 days, which was later than the period of approximately three weeks indicated by the manufacturer and others. As far as could be detected, the second to fifth pulses were not as delayed, but generally the three‐week period was also exceeded.

This delayed release of the pulse resulted in a build‐up of pasture infectivity for gastrointestinal nematode larvae and lungworm larvae. Nevertheless, this did not result in clinical gastrointestinal helminthiasis and husk in the treated groups of calves, whereas severe husk and mild gastrointestinal helminthiasis were seen in the control group.     

Epidemiological patterns of gastrointestinal and lung helminth infections in grazing calves in The Netherlands

The patterns of gastrointestinal and lung helminth infections in grazing calves were studied in two small grazing experiments carried out between May and October in 1985 and 1986, respectively, at Utrecht State University. For lungworm a very rapid translation of infective larvae was seen in both experiments, resulting in a rapid build-up of the worm burdens, and in July the second generation of Dictyocaulus caused husk. After the end of patency for lungworm, in the beginning of August, a rapid decrease in pasture infectivity, measured by pasture larval counts and worm counts of tracer calves, was observed. For the gastrointestinal nematodes the translation of infective larvae was much slower as a distinct 'midsummer increase' of pasture infectivity was not seen before the end of July. The worm counts of the tracer calves and the pasture larval counts showed that these larvae remained on pasture much longer than the lungworm larvae. As in Dictyocaulus, patency stopped in August-September in Nematodirus but not in Ostertagia and Cooperia, indicating a slower rate of development of immunity in both latter genera. In contrast to lungworm, the results indicate a clear and predictable seasonal pattern for gastrointestinal helminth infections.     

The prophylactic effect of ivermectin treatments on gastrointestinal helminthiasis of calves turned out early on pasture or late on mown pasture

A study was undertaken to ascertain the prophylactic effect on gastrointestinal helminthiasis of (1) a single ivermectin treatment of calves 3 weeks after a late turnout on mown pasture and (2) two ivermectin treatments of calves 3 and 8 weeks after an early turnout. The single ivermectin treatment after a late turnout on mown pasture appeared to be an effective control measure for infections of Cooperia and, in particular, Ostertagia. The two treatments after an early turnout were also effective, although less so than the single treatment combined with the late turnout on mown pasture. Ivermectin treatment had no effect on the faecal egg output or the pasture larval counts of Nematodirus helvetianus. The proportion of inhibited early fourth stage larvae of Ostertagia was much higher in the control group than in either of the experimental groups.     

Control of gastrointestinal parasitism with an oxfendazole pulse-release anthelmintic device

The efficacy of a pulse-release oxfendazole bolus (OPRB) against gastrointestinal nematodes was evaluated under field conditions and compared with a sustained release morantel bolus (MSRB). Three groups of 10 calves were grazed from May to September on adjacent, similarly contaminated 3-acre paddocks. One group was dosed at turnout with the OPRB, the second group with the MSRB and the third group left as nontreated controls. Pasture larval counts peaked at greater than 60,000 larvae/kg dry weight of herbage in September on the control paddock, associated with a mean egg count of 1040 eggs/g faeces and clinical symptoms. A low rise in larval counts occurred on the MSRB plot, and also low helminth egg counts. On the OPRB plot, pasture larvae and faecal egg counts were recorded only intermittently; the September egg counts were only 3.5% of those of the controls; serum pepsinogen data showed a similar picture. At the end of the experiment, the OPRB calves had a mean weight advantage of 40 kg over the controls, and 12 kg over the MSRB group. Feed intakes were highest in the OPRB group in July and September.     

A comparison of the efficacy of four different long-acting boluses to prevent infections with Dictyocaulus viviparus in calves

A field study of calves in their first grazing season tested the efficacy of four long-acting devices--a morantel sustained-release bolus, a levamisole sustained-release bolus, an oxfendazole interval bolus, and an albendazole interval bolus--against Dictyocaulus viviparus. The pasture had been previously contaminated by four calves orally inoculated with infective lungworm larvae. The calves were grazed together with four bolus-treated groups, each comprising four calves. Lungworm infection became patent in the experimentally inoculated calves between 22 and 26 days. Infection in the bolus-treated groups became patent after 54 days. The morantel bolus group excreted the most larvae, followed by the albendazole bolus group, and the levamisole bolus group. The oxfendazole bolus group excreted by far the least larvae. Eosinophil curves and ELISA titres showed that treated groups had essentially the same course of infection. The heavy infection to which the treated calves were exposed produced complete immunity in all groups. Challenge infection of 10,000 larvae at housing did not change any of the test parameters. Post-mortem examination showed only one positive calf with few worms. We concluded that when pastures are heavily infested with lungworm larvae, all boluses prevent severe clinical signs and allow build up of solid immunity, although none completely prevent excretion of larvae.     

Dictyocaulus viviparus in calves: effect of rotational grazing on the development of infections.

A study was made of the possibility of reducing lungworm infections in young grazing calves by rotational grazing for weekly periods on six paddocks. For this purpose three groups of four calves each were grazed on separate pastures in 1989, whereas a fourth group served as a permanently housed control group. Two groups of calves were infected experimentally with six doses of 10 larvae of Dictyocaulus viviparus during the first 3 weeks on pasture. In the third group, low natural infections with overwintered larvae occurred. One of the experimentally infected groups was rotationally grazed for weekly periods on six small plots while both other groups were set-stocked. Faecal larval counts and worm counts in tracer calves demonstrated lower lungworm infections in the rotationally grazed group than in both set-stocked groups. However, the numbers of worms found after challenge infection and subsequent necropsy were relatively high in the rotationally grazed group, indicating that development of immunity was less than in both other groups. Owing to the dry weather conditions in the summer of 1989, no serious clinical signs of husk developed in any of the three groups. These dry conditions, however, did not prevent the build-up of heavy pasture infectivity with gastrointestinal nematodes resulting in heavy worm burdens and serious clinical signs in tracer calves grazing for 4 days in August and September-October, respectively. This implies that rotational grazing did not have a clear effect on build-up of gastrointestinal nematode infections.     

Immunity of calves treated with an oxfendazole pulse release bolus to challenge with Dictyocaulus viviparus

Two experiments were performed to study the effect of an oxfendazole pulse release intraruminal device (OPRB) on the development of lungworm infection and immunity in calves. Infections were monitored in OPRB-treated and control calves by faecal and pastural larval counts. Levels of immunity of grazing groups and helminth-free housed groups were compared by challenge infection. Even though signs of parasitic bronchitis were seen only in control animals, sufficient immunity had developed in OPRB-treated calves to prevent disease after a substantial challenge infection. However, the degree of immunity was less than in untreated grazing control groups and there were indications that it was related to initial infection levels. These results imply that the OPRB may successfully control parasitic bronchitis, provided that pasture larval infections are sufficient to allow the development of immunity.     

Use of an oxfendazole pulse release bolus in calves exposed to natural subclinical infection with gastrointestinal nematodes

During the first grazing season a group of calves treated with an oxfendazole pulse release bolus achieved a mean (+/- sem) weight gain of 140.7 (+/- 6.7) kg compared with 106.5 (+/- 5.7) kg by a group treated once with ivermectin mid-season, and 116.9 (+/- 6.9) kg by a group which received no treatment. This economic advantage was maintained during the period of winter housing. By the end of the second grazing season, during which the animals received no anthelmintic medication, they weighed on average 20 kg more than the wholly untreated group, a difference which was not statistically significant. No signs of clinical disease were observed in either the animals dosed with a pulse release bolus or the undosed control animals during the two year trial period. The treatment with the oxfendazole pulse release bolus greatly reduced the degree of pasture contamination in the first year but in the second year those animals that had been treated in the first year developed higher worm egg counts (P less than 0.001) and thus augmented the levels of pasture contamination compared with the untreated control animals. Nematodirus battus and N filicollis both produced low grade but fertile infestations in the calves.     

Use of an oxfendazole pulse release bolus in the control of parasitic gastroenteritis and parasitic bronchitis in first-season grazing calves

The efficacy of the oxfendazole pulse release bolus system for the control of parasitic gastroenteritis and parasitic bronchitis in first-season grazing calves was evaluated in Belgium. Twenty-two calves were allocated to two groups. The calves in one group received a bolus at the time of turn out, while the other group remained untreated. The efficacy of the bolus was assessed by comparison of faecal worm egg counts, plasma pepsinogen concentrations, the antibody response to Ostertagia, Cooperia and Dictyocaulus species total plasma protein and albumin concentrations, and weight gains throughout the grazing season and the housing period. The oxfendazole pulse release bolus provided good control of parasitic gastroenteritis dominated by ostertagia. The effects of parasitic gastritis were greatly reduced as shown by the significantly lower values of serum pepsinogen and ostertagia antibody titres. The use of the bolus further reduced the adverse effects of parasitism as indicated by better liveweight gains and normal total plasma protein and albumin concentrations whereas in the untreated control group hypoproteinaemia and hypoalbuminaemia were observed. Most animals exhibited clinical signs of parasitic bronchitis at the end of the grazing season, and the bolus may not adequately control parasitic bronchitis in all cases at all times.     

Pasture study of two types of oxfendazole pulse release bolus for controlling nematodes in calves

One group of first-season calves was dosed with an oxfendazole pulse release bolus at spring turnout (April 30) and on July 15 a second group received the front-loaded oxfendazole pulse release bolus. The objective was to test the boluses for the prophylaxis or control of nematodiasis. The control group consisted of calves to which no bolus was administered. The three groups occupied separate but adjacent plots. For the first five weeks of the trial, three calves, artificially infected with Dictyocaulus viviparus grazed in each plot. Parasitic bronchitis severely affected the control calves, necessitating repeated emergency treatment, whereas administration of the bolus at turnout almost completely prevented this condition. D viviparus infection increased markedly on the control herbage in July and August but was eliminated by the end of June on pasture grazed by bolus treated calves. Treatment in mid-season with the front-loaded bolus brought an outbreak of parasitic bronchitis under control. Gastrointestinal worm egg output was satisfactorily suppressed after the administration of both boluses, resulting in reduced levels of herbage infection. Calves treated with a bolus at turnout gained significantly more weight than either the controls (P less than 0.001) or the calves treated with a front-loaded bolus in mid-season (P less than 0.01). The weight-gain of the calves treated with a front-loaded bolus was slightly but not significantly greater than that of the control calves. On the basis of faecal egg counts, the first pulse released from the standard boluses was delayed and one front-loaded bolus failed to release a dose.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunity of ivermectin treated cattle to challenge from helminth parasites in the following season

Two groups of yearling cattle which had been treated with ivermectin either three and eight, or three, eight and 13 weeks after turn out to trichostrongyle contaminated pasture in their first grazing season were exposed in the following season to natural challenge with helminth parasites. To assess their immunity to this challenge each group shared a pasture with parasite naive first season calves. No anthelmintic treatments were administered at any time during the year. Throughout the grazing period the yearlings showed normal respiratory rates, negative faecal lungworm larval counts, and, relative to the calves, low faecal trichostrongyle egg counts. All the first season calves developed patent lungworm infections and on one occasion the mean respiratory rates of each group of calves were significantly greater than those of the yearling cattle. At the end of the grazing period, from early May until late September or October 1986, the cattle were removed from pasture and together with parasite naive controls challenged with either 10 or 22 third stage larvae of Dictyocaulus viviparus/kg bodyweight and necropsied between 18 and 23 days later. Although the experimental challenge resulted in relatively heavy lungworm infection of the naive controls, none of the yearlings and only three of the 11 calves which had been at pasture were found to be infected. However, large numbers of arrested fourth stage larvae of Ostertagia ostertagi were present in all the naturally infected yearlings and calves.     

Studies on the epidemiology of bovine parasitic bronchitis.

In the West of Scotland the epidemiology of parasitic bronchitis in grazing calves was studied over a two year period with the aid of tracer calves and herbage examinations for Dictyocaulus viviparus larvae. The observations of both years emphasised the importance of overwintered lungworm larvae as a source of disease. In the first year it was shown that the ingestion and development of these overwintered larvae were, by themselves, directly responsible for severe morbidity, high faecal larval counts and deaths. In the second year it was shown that pasture ungrazed during the winter and spring and from which a hay crop was removed in mid-summer was still capable of producing clinical parasitic bronchitis in susceptible calves within three to four weeks of their introduction in later summer. In both years there was some evidence that the outbreaks appeared to be associated with the sudden availability of infective larvae on the herbage. The possibility that such larvae may have survived for many months in the soil is discussed. Despite the heavy challenge with lungworm larvae experienced by the grazing calves in the first year those vaccinated with lungworm vaccine survived, their clinical signs were mild and of short duration and their faecal larval output was greatly reduced.     

Concurrent use of the oxfendazole pulse release bolus and the monensin rumen delivery device in young grazing cattle

When they were turned out to grass in May 1987 for their first season, 10 calves were dosed with a 5 x 750 mg oxfendazole pulse release bolus (OPRB) and a monensin sodium rumen delivery device (RDD); eight calves received one OPRB; 10 calves received one RDD and eight calves received neither bolus. Each group was set-stocked on individual paddocks which had been grazed during the previous season by cattle which developed clinical parasitic gastroenteritis and bronchitis (husk). In July, before they were due to be moved to new pastures in mid-summer, and before they were dosed strategically with levamisole HCl, some of the calves not dosed with an OPRB succumbed to clinical parasitic gastroenteritis and husk and received emergency anthelmintic treatment, after which no further clinical episodes occurred. The 'dose and move' strategy was implemented in early August after which both groups not dosed with an OPRB were set-stocked together until the trial ended on October 14, 147 days after turn out. The two groups of calves which had received the OPRB were also moved to new pasture and set-stocked together until the end of the trial. No evidence of clinical helminthiases developed in either of the two groups of calves dosed with OPRBs and their faecal worm egg and larval counts, and plasma pepsinogen activities remained low. They gained significantly more weight than the two groups of calves not dosed with OPRBs (P less than 0.001). The bolus types were compatible and induced no untoward side-effects when used together.     

Assessment of an oxfendazole pulsed release bolus for control of parasitic gastroenteritis in calves in a rotational grazing system

A group of 71 Friesian bullocks, aged six to nine months, vaccinated against lungworm, were randomly allocated on a liveweight basis to two groups of 40 and 31 animals. At turn-out each calf in the group of 40 calves was dosed orally with a pulsed release bolus designed to deliver five doses of oxfendazole at regular intervals during a period of up to 130 days, the first dose being released about 21 days after administration. The group treated with the bolus grazed 2.4 ha and the control group grazed 3.6 ha of permanent pasture for six weeks before having additional access to similar areas of silage aftermath. The control group was treated 99 days after turn-out and when they were housed with fenbendazole (7.5 mg/kg). Faecal worm egg counts, plasma pepsinogen activities, pasture larval counts and liveweights were recorded fortnightly. Significant reductions in worm egg counts and plasma pepsinogen activities were recorded in the calves dosed with the pulsed release bolus together with significant improvements in the liveweight of younger calves compared with control animals. Pasture larval counts were lower in the fields grazed by animals treated with the bolus.     

Studies on the interaction between an irradiated bovine lungworm vaccine and a morantel sustained release bolus

The interaction of the morantel sustained release bolus with the development of immunity in calves vaccinated with two doses of gamma irradiated (40 Kr) Dictyocaulus viviparus larvae was investigated under laboratory conditions. A total of 37 helminth-naive calves were used. Eight calves were used in the first part of the study to test the efficacy of a larval vaccine prepared by using gamma rays delivered from a cobalt source. In the second part of the study, four groups of four groups of four calves each were vaccinated and of these, all the animals in two groups each received a bolus. The remaining three groups (two groups of four and one group of five calves each) remained nonvaccinated with each animal in one group receiving a bolus. All the calves were challenged with approximately 2000 lungworm larvae four months postvaccination. In order to simulate possible field conditions, two of the vaccinated groups and two of the nonvaccinated groups were given a trickle infection of 800 lungworm larvae over a four-week period, three months prior to challenge. Based on a comparison of clinical signs, pathology and lungworm burdens at necropsy, the vaccination of the calves conferred a significant degree of protection (P less than 0.001) to a subsequent challenge compared with controls. The introduction of a morantel sustained release bolus and/or a trickle infection had no effect on the high degree of protection engendered by the vaccination. Nonvaccinated calves given a trickle infection, with or without a bolus, were also highly immune to challenge.     

The use of the morantel sustained release bolus under special farm practices (deprime system) in France

The efficacy of the morantel sustained release bolus in controlling gastrointestinal and lungworm parasites when used in first-season grazing animals which followed older animals onto spring pasture (deprime system) was assessed in three trials conducted in Normandy, France. In each trial first-season grazing calves were equally allocated onto two separate but equivalent paddocks where they remained throughout the grazing season. A morantel sustained release bolus was administered to one group of animals at turnout, the other group remained as controls. The effect of the treatment on contamination of pasture (herbage larval counts and tracer worm counts), on faecal worm egg and lungworm larval counts, and on weight gain performance of the principal animals was assessed. In all three trials, worm egg output in the bolus-treated animals was substantially lower throughout the season compared with the control animals. Worm burdens of tracer calves grazing pastures of the treated cattle were also reduced compared with tracer calves grazing control pastures. Clinical parasitic gastroenteritis occurred in the control animals but not in the bolus-treated animals in one trial. Overall the bolus-treated animals outperformed the controls by a mean weight gain advantage of 10.5 kg (P less than 0.01).     

Chemoprophylaxis and immunity to parasitic bronchitis in cattle — a field experiment comparing topical ivermectin and an oxfendazole intraruminal device

Seeder calves infected with Dictyocaulus viviparus were used to contaminate a field divided into three similar paddocks. Twenty-four autumn-born calves were allocated to three matched groups; one group was given topical ivermectin treatments (0.5 mg/kg) at 3, 8 and 13 weeks after turnout (Day 0); each member of a second group was given an oxfendazole pulse-release intraruminal device (OPRB) at turnout; while a third group was kept as untreated controls to monitor the natural epidemiological pattern of events. Severe pasteurella pneumonia exacerbated by lungworm infection occurred in the controls after Day 24. Two died and repeated doses of antibiotic and anthelmintic therapy were necessary to save the remainder. Clinical signs were much milder in the ivermectin and OPRB groups and resolved with only a single dose of antibiotic. The OPRB group excreted some lungworm larvae at this time, but none was detected in the faeces of the ivermectin group during the grazing season. At housing, five calves from each group and four lungworm-naive calves were challenged with D. viviparus larvae. The infection became patent in all challenge-control calves, but no larvae were passed by any of the trial animals. Post-mortem worm-counts revealed percentage takes for the challenge controls, trial controls, ivermectin and OPRB groups of 16.7, 0.01, 0.9 and 0.2, respectively. All trial groups had therefore developed a substantial immunity.     

A pilot study of the efficacy of topical ivermectin against lungworm in young red deer (Cervus elaphus)

Three groups of ten 4-month-old red deer (Cervus elaphus) calves naturally infected with lungworm (Dictyocaulus viviparus) were treated with either oral ivermectin (200 microg/kg), topical (pour-on) ivermectin (500 microg/kg) or oral oxfendazole (5 mg/kg). Faecal larval counts for lungworm were undetectable or very low for 14 days after treatment with oxfendazole, 28 days after treatment with oral ivermectin and for 49 days after treatment with topical ivermectin. This pilot study suggests that the topical formulation of ivermectin was very effective against lungworm and had a more persistent action than the oral ivermectin formulation in young red deer.     

Control of naturally acquired bovine parasitic bronchitis and gastroenteritis with an oxfendazole pulse release device

Four groups, each of six male Friesian calves, were set-stocked on separate 0.66 ha paddocks from May 7 until October 23 1986. Each of the animals in groups 1 and 4 was dosed with an oxfendazole pulse release bolus at turn out whereas the animals in groups 2 and 3 were left untreated. Parasite-free naive tracer calves were introduced into each paddock for a limited period 12 days after turn out and again at the end of the trial. No adverse reactions or clinical signs were observed in either of the groups of calves which received boluses. The development of clinical parasitic gastroenteritis in both the untreated groups necessitated the humane slaughter of two animals and emergency anthelmintic treatment of the remainder. The lower plasma pepsinogen concentrations, and lower faecal egg and larval counts and worm burdens post mortem, together with the absence of clinical signs of parasitic gastroenteritis and bronchitis in the treated calves, confirmed the high efficacy of the bolus treatment.     

A comparison of lungworm faecal larval counts and trichostrongyloid faecal egg counts between red deer (Cervus elaphus) and red deer x wapiti F1 hybrids

To determine if breed differences in susceptibility to trichostrongyloid and lungworm infection exist, two groups of weaner deer containing seven red deer and red deer x wapiti F1 hybrids were compared using faecal egg counts and faecal larval counts. All animals were run on the same pasture at the same time and treated with the same anthelmintics at the same time. Results indicated that there were significant differences between red deer and red deer x wapiti hybrids, with red deer having higher faecal lungworm counts and red deer x wapiti hybrids having significantly higher faecal egg counts. It is likely that these differences were due to breed. Differences in the efficacy of anthelmintic treatments were also noted between the two groups, with oral oxfendazole being less effective at reducing faecal lungworm counts in red deer X wapiti hybrids than red deer.