Efficacy of Daily Pyrantel Tartrate (Strongid C) against Strongyles in Ponies on Pasture

A clinical trial was conducted with 2- to 3-year-old ponies to determine the effectiveness against strongyles of 2.64 mg pyrantel tartrate/kg body weight administered in the daily ration throughout a pasture season in Canada. Ten ponies were given the anthelmintic, and 10 were not treated and served as controls. Each group of ponies was on a separate pasture. The mean strongyle eggs/g of feces for each group, before treatment and turnout to pasture, was greater than 2,200. Thereafter, the mean eggs/g feces for the untreated group remained high (1,405−2,294) and those for the treated group decreased markedly to, and remained at, very low levels (0.2−16.8). Strongyle larval counts for the pasture with the untreated ponies rose to 26,790 larvae/kg dry herbage in August, whereas that for the treated group was 610 larvae/kg dry herbage. At the end of the season, two ponies from each group were isolated for 6 weeks and necropsied. The mean number of strongyles in the untreated and treated ponies was 69,288 and 8,452.5, respectively. In the untreated ponies, 21 species of strongyles were found, and approximately 84% of them were from eight species of cyathostomes. In the treated ponies, 14 species of strongyles were found, and approximately 77% were from one species, Cylicostephanus minutus (52.0%), and immature cythostomes (25%). Adverse reactions were not observed in any of the treated ponies. Pyrantel tartrate was highly effective in significantly reducing the strongyle egg and pasture larval counts and the transmission of strongyles during a pasture season.     

Comparison of two control systems for cyathostome infections in the horse and further aspects of the epidemiology of these infections

The small strongylid infections of two groups of three yearling female Shetland ponies and one yearling Shetland tracer pony were studied. One group was set stocked from April to November and was treated monthly with 5 mg kg-1 albendazole from two days before turnout until July. The other group grazed similar pasture until July, was treated with 5 mg kg-1 albendazole and subsequently removed to pasture grazed by sheep from April to July. The tracer ponies were added to both groups in September. The efficacy of both methods was not completely satisfactory probably because of low efficacy of anthelmintic treatment. There were no significant differences between the cyathostome burdens of the two groups. A high proportion of the cyathostome populations of all ponies consisted of inhibited early third stage larvae (L3). The finding of low numbers of immature fifth-stage worms in the tracer ponies indicated that the considerable adult burdens in the permanent ponies originated from infection picked up before the tracer ponies were added. In the group which was removed to sheep pasture after treatment in July it was likely that the majority of the adult worm burden had been ingested as infective larvae before treatment.     

Observations on the epidemiology and control of Strongylus vulgaris infections

The epidemiology and control of helminth infections in the horse were studied in four small grazing experiments between 1981 and 1984 at the University of Utrecht. At autopsy in November or December negligible Strongylus vulgaris burdens were found in the cranial mesenteric artery of four groups of ponies, which had been treated with an anthelmintic in July and subsequently transferred to a clean pasture. Considerable arterial S. vulgaris burdens were seen in three groups of ponies which were treated with an anthelmintic in July without a move to clean pasture, and in another group of ponies in 1984, which was set stocked on a pasture used for horses in 1983 and which was treated with an anthelmintic (albendazole) 2 days before turnout in April and subsequently in May, June and July. A tracer pony, grazed with this group between the middle of September and the middle of November, harboured an even higher burden of arterial S. vulgaris larvae. The arterial S. vulgaris in the latter group could not be the result of contamination of the pasture with S. vulgaris eggs before July, as in the three other groups with considerable arterial S. vulgaris burdens. Pasture larval counts showed that S. vulgaris larvae do not only overwinter, but are able to survive in considerable numbers until autumn, longer than most other gastrointestinal nematodes. There were some indications that translation of infective larvae, which overwintered on pasture in some free living stage, occurred between May and July.     

Response of young cattle to anthelmintic treatment during autumn in a Mediterranean-type climatic environment

A worm control programme in which heifers were treated with anthelmintic on three occasions during autumn, was tested in the Mediterranean-type climatic environment of south-west Western Australia. The experiment aimed to determine if the treatments would prevent the heifers contaminating their pastures with worm eggs during autumn, thereby improving their growth performances the following winter. An attempt was made to measure the availability of infective larvae of abomasal worms on the heifers' pastures during early winter by counting the worms in steers, previously of low worm status, that grazed with the heifers from late autumn until the start of mating in mid-winter.

The anthelmintic treatments reduced the contamination of pasture for most of autumn. The treated heifers that grazed these pastures grew faster, and by the start of mating two months after the last treatment were about 22 kg heavier, than untreated heifers grazing contaminated pasture. At the end of mating six weeks later the difference was 45 kg in favour of the treated heifers. At this time half the heifers grazing contaminated pasture were treated with anthelmintic. The following month these heifers grew faster than those left untreated, but by late November they had not attained the wieght of the heifers grazing uncontaminated pasture.

The heifers that grazed uncontaminated pasture produced more calves the following autumn than did those grazing contaminated pasture. The abomasal worm counts of the steers, with a mean of about 46 000 worms, failed to reveal any difference between treatments in the availability of larvae of abomasal worms on pasture. However, it was concluded that the treatments probably exerted their effect on growth rates by reducing the number of infective larvae ingested by heifers grazing the uncontaminated pasture during winter.     

Seasonal translation of infective larvae of gastrointestinal nematodes of cattle and the effect of Duddingtonia flagrans: a 3-year pilot study

A study was conducted over 3 years (1998-2000) to investigate larval availability of gastrointestinal nematodes from faeces of cattle reared under different parasite control schemes. These cattle were part of a parallel, but separate grazing trial, and were used as donor animals for the faecal material used in this experiment. At monthly intervals, faeces were collected and pooled from three groups of first-season grazing cattle. These groups were either untreated, ivermectin bolus treated or fed the nematophagous fungus Duddingtonia flagrans. The untreated and fungus treated animals were infected with gastrointestinal nematodes and the number of eggs per gram (epg) pooled faeces ranged between 50 and 700 in the untreated group and between 25 and 525 epg in the fungus treated group. Each year between June and September, artificial 1 kg dung pats were prepared and deposited on pasture and protected from birds. The same treatments, deposition times and locations were repeated throughout the study. Larval recovery from herbage of an entire circular area surrounding the dung pats was made in a sequential fashion. This was achieved by clipping samples in replicate 1/4 sectors around the dung pats 4, 6, 8 and 10 weeks after deposition. In addition, coinciding with the usual time of livestock turn-out in early May of the following year, grass samples were taken from a circular area centred where the dung pats had been located to estimate the number of overwintered larvae, which had not been harvested during the intensive grass sampling the previous year. It was found that recovery and number of infective larvae varied considerably within and between seasons. Although the faecal egg counts in 1999 never exceeded 300 epg of the faecal pats derived from the untreated animals, the abnormally dry conditions of this year generated the highest level of overwintered larvae found on herbage in early May 2000, for the 3 years of the study. Overall, biological control with D. flagrans significantly reduced larval availability on herbage, both during and between the grazing seasons, when compared with the untreated control. However, the fungus did not significantly reduce overwintered larvae derived from early season depositions (June and July), particularly when dung pats disappeared within 2 weeks after deposition. Very low number of larvae (<3 per kg dry herbage) were sporadically recovered from grass samples surrounding the ivermectin bolus faecal pats.     

Alternate grazing of horses and sheep as control for gastro-intestinal helminthiasis in horses

Gastro-intestinal helminth of a group of three yearling mare Shetland ponies, which were set-stocked on a small pasture from February until September, were compared with those of a similar group of ponies, which grazed a similar pasture from February to July and subsequently was removed to a pasture which had been grazed by sheep from April to July. In addition both groups were treated with cambendazole when the latter group was removed to the sheep pasture.Pasture larval counts and worm counts demonstrated that the group grazed after the sheep acquired considerably smaller burdens of nematodes of the subfamilies Cyathostominae and Strongylinae, but considerably higher burdens of Trichostrongylus axei than the group which remained on the same pasture. The T. axei infections in the former group caused an increase in the serum pepsinogen levels within two weeks after removal to the sheep pasture followed by a gradual decrease. At necrospy T. axei populations consisted almost exclusively of inhibited early third state larvae.     

Epidemiology and control of equine strongylosis at Newmarket

Seasonal rises in mean faecal egg output were observed in grazing ponies in spring (578 eggs per gram) and in summer (930 epg) on 30 April and 2 September, respectively, in untreated ponies. Pasture infectivity reached a peak of 18,486 third stage larvae (L3)/kg on 17 September, two weeks after peak egg counts, coincidental with abundant September rainfall (103.0 mm). Differentiation of infective larvae from pasture showed the cyathostomes (small strongyles) to be predominant, but Trichostrongylus axei assumed major importance from late August to October. The large strongyles were rarely detected: Strongylus vulgaris was found only once and S edentatus only twice. The most effective parasite prophylaxis was achieved by twice weekly removal of faeces. In this group, concentrations of infective L3 on pasture reached a maximum of 1000 L3/kg, compared to 18,486 L3/kg for a control group and 4850 to 10,210 L3/kg for anthelmintic treatment groups. The removal of faeces increased the grazing area by about 50 per cent, by eliminating the characteristic separation of horse pasture into roughs and lawns. Spring and summer anthelmintic treatments of mature ponies with oxibendazole were effective in reducing the late season rise in pasture infectivity to 4850 L3/kg, but treatment of young ponies (mainly yearlings) with ivermectin every eight weeks or oxibendazole every four weeks resulted in pasture infectivity as high as 10,000 L3/kg. There was evidence of cyathostome resistance to benzimidazole drugs.     

Efficacy of the morantel sustained-release bolus in grazing cattle in North America

The efficacy of using a bolus containing morantel in a sustained-release preparation for controlling naturally acquired gastrointestinal parasitic infections in weaned calves and yearling cattle was investigated during the 1982 grazing season at selected sites in the United States and Canada. According to a common trial design under various climatic and management conditions, 10 field trials were conducted with the bolus. At the time of spring turnout, a bolus was administered to each calf or yearling in the treated group. Then, treated and control cattle grazed separate but equal areas of divided pasture(s). The epidemiologic pattern of parasitic gastroenteritis in control animals and the effect of treatment on this pattern was determined in each trial. Safety and practicality of use of the bolus also were established. When compared with untreated cattle (control), those given the bolus deposited significantly (P less than 0.05) fewer worm eggs (89% reduction) during the first 90 days of the grazing season, as well as significantly fewer (P less than 0.05) worm eggs (84% reduction) during the entire grazing season. Consequently, during the second half of the grazing season, larval populations on treated pastures remained significantly (P less than 0.05) lower (66% reduction), compared with numbers of larvae found on control pastures. For pastures grazed by treated and control cattle at trial initiation, mean worm counts recovered from tracer calves were equal, indicating comparable pasture contamination at the beginning of the grazing season.(ABSTRACT TRUNCATED AT 250 WORDS)     

Epizootiology of helminth parasitism in a beef cow/calf herd in Minnesota.

To test the effect of a parasite control program for cattle, 2 groups of similar composition were grazed on separate, but equivalent, improved pastures. Cattle in 1 group were treated with fenbendazole at 5.0 mg/kg of body weight at the time they were turned out on pasture in the spring and again at midsummer, when the cattle were moved to a new pasture. The control group was not treated. Parasite egg counts were significantly (P less than 0.04) lower in the treated group. Trichostrongyle-type eggs were the most prevalent throughout the year, except in the month of May, when Strongyloides papillosus eggs were predominant. The number of worms recovered from tracer calves was lower for those on pastures where the treated group grazed than for those on the control group's pasture. The most consistently recovered parasite was Ostertagia ostertagi, and hypobiosis was observed.     

Possible resistance of small strongyles from female ponies in The Netherlands against albendazole

To determine resistance of small strongyles to albendazole, 3 female ponies (group 1) were grazed on a pasture from May to November 1985 and were treated with 7.5 mg of albendazole/kg of body weight, PO, 2 days before turnout in May and again in June and in July. Three other female ponies (group 2) grazed on a similar pasture from May to July, were treated with 7.5 mg of albendazole/kg, and were removed to another pasture until November. In December, ponies from both groups were treated with 7.5 mg of albendazole/kg, and 8 days later, they were euthanatized and necropsied for a critical test. Worm egg counts in the ponies' feces revealed that the May treatment of group 1 and the July treatment of group 2 were more effective than were later treatments. Numbers of small strongyles were higher in group 1 than in group 2. Efficacy of treatment against all developmental stages of small strongyles was higher in group 2 than in group 1. Efficacy was low in both groups against parasitic 3rd- and 4th-stage larvae. Fifteen species of small strongyles were identified at necropsy. Efficacy was limited against adult Cyathostomum coronatum, Cya labratum, Cylicostephanus calicatus, and Cyl poculatus in both groups; Cylicocyclus nassatus, Cyl minutus, and Cyl longibursatus in group 1; and Cya labiatum in group 2. Efficacy was 100% against Cya catinatum, Cyl goldi, and 5 other species that were found in low numbers.     

Efficacy of ivermectin controlled-release capsules for the control and prevention of nasal bot infestations in sheep

Objective To investigate the therapeutic and prophylactic efficacy of an ivermectin controlled-release capsule against nasal bots (Oestrus ovis) in sheep.
Design Trial 1 – A pen study with controls. Trial 2 – A field study with controls.
Animals Trial 1 – Forty Merino wethers with natural infestations of nasal bot were used. Trial 2 – One hundred nasal bot-free wethers were used.
Procedure Trial 1 – Ten randomly selected animals were slaughtered and the heads split and examined to confirm bot infestation. Fifteen animals were allocated to untreated controls and 15 to treatment with a controlled-release capsule delivering ivermectin at ≥ 20 μg/kg/day for 100 days. Twenty-nine days after treatment the sheep were killed and examined for nasal bots. Trial 2 – Nasal bot-free sheep were allocated to two groups of 45 animals. One group was untreated the other sheep were treated with capsules as above. The sheep were grazed as a single group exposed to natural challenge from O ovis . Ninety days after treatment the animals were slaughtered and examined for nasal bot infestation.
Results Trial 1 – Live O ovis larvae were recovered from 60% of control sheep. No live larvae were collected from treated sheep. Trial 2 – Forty-one percent of untreated sheep harbored nasal bot infestations. No live larvae were collected from any treated animal.
Conclusion Treatment with a single ivermectin controlled-release capsule was 100% effective against existing infestations of O ovis and as a prophylactic treatment for this parasite.     

Utilisation of the persistent anthelmintic activity of ivermectin in a preventive drenching programme for dairy calves

A study was undertaken to assess whether the persistent anthelmintic effect of ivermectin in cattle would allow an extension of the drenching interval in the currently recommended preventive drenching programme for the control of gastrointestinal nematode infection in dairy calves. A comparison was made of the parasitological and production responses of treatment groups of calves, grazing replicated plots, receiving either six drenches of oxfendazole at four-weekly intervals or four subcutaneous treatments with ivermectin at six-weekly intervals. Compared with the levels of infective larvae on pasture grazed by untreated control calves, mean larval numbers on pasture grazed by ivermectin and oxfendazole treated calves were 94.3% and 98.3% lower, respectively, during the period of maximum larval availability (March-May). Mean liveweight gains (December-August) of the treated groups (101.4kg and 110.2kg respectively) were not significantly different, but both were highly significantly different from that of the untreated controls (57.4kg). Mean plasma pepsinogen levels for the ivermectin, oxfendazole and control groups over the period of maximum values (June-August) were 1.92 i.u., 1.72 i.u. and 5.53 i.u., respectively. The difference between the treated groups was not statistically significant but both were highly significant different from the control group. The present results indicate that four treatments with ivermectin (subcutaneously) at six-weekly intervals achieved a similar level of prophylactic control to that effected by six treatments with oxfendazole at four-weekly intervals.     

Overwintering of larvae of the cattle lungworm (Dictyocaulus viviparus) on pasture in Kentucky

Seventeen dairy calves, raised lungworm-free, were used in an experiment to determine whether lungworm (Dictyocaulus viviparus) larvae survived on a pasture in central Kentucky during the winter of 1979/1980. On Apr 22, 1980, the calves were placed on pasture. Three calves were put on pasture A, on which no cattle had grazed for over 20 years. Fourteen calves were put on pasture B, which had been vacant since Dec 12, 1979 (132 days before beginning of experiment), when several lungworm-infected calves had been removed from the pasture. Fecal samples from the 17 calves were examined for lungworm larvae at weekly intervals for about 6 weeks; lungworm larvae were not found in any of the 3 calves on pasture A, but were found in 12 of 14 (86%) calves on pasture B. One calf from pasture A and 3 calves from pasture B were euthanatized 37 days after being placed on pasture; lungworms were recovered from 1 calf from pasture B.     

Seasonal development of Cyathostominae larvae on pasture in a northern temperate region of the United Kingdom

A study following the development of Cyathostominae from egg to the infective larval third stage was conducted from April to December 2001 in west central Scotland. Duplicate samples (1 kg) of naturally infected faeces were placed on a 78 cm2 plot each week on a cyathostomin-free pasture. Subsamples of the grass surrounding the faecal plot were collected weekly on four occasions and the number of larvae obtained determined. Few larvae were recovered in the first week of development of individual plots, followed by a rise in the numbers of larvae in second, third and fourth weeks of development of each sample. The climatic conditions were seen to have an effect on the rate of development. Specifically, from multilevel, multivariable linear regression models it was evident that the factors associated with numbers of infective larvae recovered from pasture were the time since the faeces samples were laid down, the average temperature and rainfall during the previous week, as well as the interaction between temperature and rainfall. Conversely, from the model, the number of larvae recovered from pasture was associated with neither the number of eggs within the faeces samples placed on the plots nor with the viability of these eggs.     

The combined effect of fenbendazole treatment and a move to aftermath 7 or 9 weeks after turnout on Dictyocaulus viviparus infections in calves

A grazing study was performed with the main objective of examining the effect of fenbendazole (FBZ) in a ‘dose and move’ system on nematode infections in calves with special emphasis on Dictyocaulus viviparus.

Three groups of six calves were grazed from May to October 1993. One group (DM7) was treated with FBZ and moved to aftermath (pasture which had only been mown) 7 weeks after turnout. The second group (DM9) was similarly treated and moved 9 weeks after turnout and the third group served as untreated pasture control group (PC) and was moved to aftermath 9 weeks after turnout.

FBZ treatment removed adult lungworms from DM7 and DM9. Tracer calves grazed during the first 7 or the first 9 weeks after turnout acquired mean burdens of 18 and 125 lungworms, respectively. In PC faecal larval counts increased until the end of August. Most of the animals in this group were then suffering from lungworm disease and emergency treatment with ivermectin was given. In both FBZ-treated groups, larvae reappeared in the faeces of some of the calves 4–5 weeks after treatment. Subsequent reinfection resulted in higher mean faecal larval counts in both groups 2 months after treatment, although variation in faecal larval counts was high. In DM7 values tended to be higher than in DM9. These higher larval counts were associated with mild signs of parasitic bronchitis in some calves of DM7, whereas no signs were seen in DM9.

At the end of the experiment, all calves, and also a group of six permanently housed non-infected control calves (HC), were infected experimentally with 5000 D. viviparus larvae to evaluate development of immunity. The worm counts at necropsy showed that all calves on pasture had developed immunity.     

Strongyle infections in ponies. II. Reinfection of treated animals.

Five of seven ponies whose strongyle worm burdens had previously been removed or markedly reduced by repeated thiabendazole treatments were reinfected with doses ranging from 100,000 to 500,000 small strongyle infective larvae. Reinfection of ponies resulted in the development of clinical signs characterized by abnormal feces, marked loss of weight and delayed shedding of winter hair coats. An abrupt increase in circulating eosinophils occurred during the first three weeks following reinfection. Patent infections developed in all ponies with worm eggs appearing in the feces from 12 to 15 weeks after receiving infective larvae. Worm egg outputs followed a cyclic pattern with approximately four to five peaks in egg output per year. There was an abrupt drop in the high worm egg counts in two untreated ponies approximately two and a half years after reinfection. No worms were recovered in the feces of these animals when they were subsequently treated, suggesting that a depletion in the number of inhibited larvae present in these ponies might have occurred.     

The effect of ivermectin treatment against inhibited early third stage, late third stage and fourth stage larvae and adult stages of the cyathostomes in Shetland ponies and spontaneous expulsion of these helminths.

A controlled and critical test on the efficacy of ivermectin against larval and adult stages of the cyathostomes was carried out in six yearling castrated male Shetland ponies. The ponies grazed together as one group from 3 May to 4 October 1990, after which they were housed. Three ponies were treated with ivermectin on 29 October while the others served as controls. The shedding of helminths in the faeces was followed in all ponies until necropsy on 14 November. Comparison of worm counts of both groups before and after necropsy showed no evidence for an effect of ivermectin against inhibited early third stage larvae (EL3) and mucosal late third stage (LL3) and fourth stage larvae (L4). However, a high, but not 100%, efficacy was observed against adults and lumenal L4. A remarkable observation was the high incidence of spontaneous expulsion of L4 and adult populations of some species in two of the untreated ponies.     

THE SURVIVAL OF TAENIA PISIFORMIS EGGS UNDER LABORATORY CONDITIONS AND IN THE FIELD ENVIRONMENT

This study reports on the long-term survival of Taenia pisiformis eggs held under controlled laboratory conditions and in the external environment. Egg viability was assessed by feeding the ova to susceptible rabbits. In the laboratory experiment dried eggs were stored under 4 different temperature and relative humidity regimes. At various time intervals eggs were removed from these environments and fed to rabbits which were subsequently killed and the number of viable cysticerci within them counted. The results show that a high temperature (38 degrees C) and to a lesser extent, a low humidity (33%) are quickly lethal to eggs and few survive for more than 7 days. However, at 4 degrees C and a relative humidity of 90%, some eggs were still viable after 300 days. At the lower temperature there was a noticeable interaction between temperature and relative humidity. For the field study a small area of pasture was enclosed by a rabbit-proof fence and hessian screen. The pasture was first shown to be substantially free of extraneous contamination with T. pisiformis ova and was then artificially seeded with a large number of eggs. Fresh groups of susceptible rabbits were grazed on this pasture at intervals thereafter. The results, expressed as the mean number of cysticerci recovered from rabbits, show that eggs remain viable for several months during winter and early spring, but in summer no viable eggs could be demonstrated after a period of 2 weeks.     

Effects of Mixed Grazing of First- and Second-year Calves on Trichostrongylid Infections in Lithuania

The objective of this study was to examine whether susceptible calves grazing together with second-year resistant heifers are less exposed to trichostrongylid infection than are calves grazing on their own. Two groups of animals representing each age category were turned out onto pasture on 24 May 1997 and grazed at comparable stocking rates. The grazing of calves and heifers together was compared to groups of each age category grazing separately. The results indicated that herbage larval counts were significantly reduced in the second part of the grazing season on the plot grazed by the mixed group compared to the plot grazed by the first-season calves only. The mixed grazing strategy protected the young calves and no clinical signs were observed in this group, while most of the calves that grazed alone exhibited clinical signs. The availability of herbage was reduced towards the end of the season, with subsequent competition for the grass forcing all the animals to graze the tufts around the faecal pats, where the quality of the grass is poor and the numbers of infective larvae are high. The effect of this was visible in the form of increased parasite burdens in the calves that were grazed together with the heifers, confirmed by increased blood serum pepsinogen concentrations and reduced daily weight gains in the second part of the grazing season. The lower numbers of infective larvae on the pasture were probably achieved through the heifers ingesting many of the larvae but subsequently depositing relatively few eggs, since they had acquired some degree of resistance against trichostrongylid infections during their first grazing season. Thus they did not suffer any parasitological ill-effects during mixed grazing with first-season calves.     

Suppression of the pathogenic effects of Strongylus edentatus larvae with thiabendazole.

Four pony foals were inoculated with Strongylus edentatus infective larvae and on days 3 and 4 postinfection two of the ponies were treated with thiabendazole, each at the rate of 440 mg/kg of body weight. Total circulating eosinophil counts in untreated ponies increased to over 1700 per cu mm after the second week postinfection. In the treated ponies as well as in an uninfected untreated pony eosinophil counts did not increase beyond 100 per cu mm. At necropsy on day 35 postinfection the cecum, colon and omentum of treated ponies were normal and few tracks were present on the surface of the liver. In untreated ponies nodules were observed on the serosal surface of the cecum and right ventral colon and white foci and tracks were numerous on the surface of the liver. A total of 53 fourth stage larvac was recovered from the livers of the thiabendazole treated ponies and 1194 from the untreated ones.