The origin of winter populations of infective larvae of nematode parasites of cattle in a Mediterranean-type climatic environment

An experiment to determine the origin of populations of infective larvae of cattle nematode parasites on pasture during winter was conducted in south-west Western Australia. Six pasture plots were contaminated with worm eggs by grazing worm-infected cattle for periods of a month during summer and autumn. Each plot was contaminated at a different time from the rest. The levels of infective larvae were determined by counting the worm burdens of tracer calves which test-grazed the plots the following winter.Tracer calves which grazed the plots contaminated during summer acquired few worms, whereas those that grazed the plots contaminated during autumn acquired many worms. It was concluded that the hot, dry conditions prevailing during summer and early autumn prevented the development of eggs or survival of larvae in dung pats or free on pasture. In this environment, a programme of worm control which relied on administration of anthelmintic to grazing cattle to prevent autumn contamination of pasture would be most likely to succeed if the first treatment was given in early autumn.     

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.     

Observations on the epidemiology of Dictyocaulus viviparus in north west England

A five year ley pasture was used as a source of natural infection with Dictyocaulus viviparus for cattle in anthelmintic trials. Pasture larval counts, faecal larval counts of permanently grazing calves and lungworm burdens harboured by tracer calves were monitored in three grazing seasons to assess the pattern of infection. Carrier calves were introduced at the beginning of the grazing season in the first two years of the study but not in the third. In the fourth year the pasture was subdivided into two paddocks where overwintered infection with and without carrier infection were compared. A control paddock exposed to carrier infection but no overwintered infection was also monitored. Pasture larvae survived the winter but carrier infection appeared to make a larger contribution to pasture larval counts and the onset of parasitic bronchitis in susceptible calves. In the absence of grazing cattle at the end of the grazing season the concentration of D viviparus larvae on the herbage fell rapidly to undetectable levels. Discrepancies between contamination of herbage by infective D viviparus larvae and infectivity of pasture for susceptible cattle occurred in all years but were particularly marked on the third year when natural immunity appeared to influence the number of lungworms accumulating in tracer calves. Failure to recover lung worms from tracer calves cannot be regarded as an accurate indication of lungworm free pasture. In the first three years the proportion of the lungworm population which was inhibited in tracer calves was higher early and late in the grazing season and negligible in mid season. This suggests that a predisposition to inhibition in larvae which have overwintered on pasture may influence the time of onset of parasitic bronchitis in the next grazing season, but results from the fourth year did not support this hypothesis.     

Observations on the resumption of development of inhibited Ostertagia, Cooperia and Nematodirus infections in calves stabled overwinter.

Two groups of three month old, parasite-free calves grazed a permanently infected pasture for 14 days, Group A during the first two weeks of September and Group B during early November. Half of each group was killed 14 days after removal from the pasture and the remainder stabled overwinter before slaughter and parasitological examination. Marked inhibition of development occurred for Cooperia oncophora with a variable lower level of inhibition for Ostertagia ostertagi and practically none for Nematodirus helvetianus in those calves grazing late in the fall. Under the conditions of this study, inhibited Cooperia larvae resumed development in several calves soon after they were stabled while small numbers of Ostertagia resumed development regularly during the winter and spring with a considerable number of Ostertagia still present when the calves were slaughtered at the end of the stabling period. On the other hand, Nematodirus and practically all Cooperia worms were lost during the stabling period. In three of seven calves grazing late fall pastures, large Cooperia infections were either not established or failed to become patent.     

Infection with Ostertagia ostertagi in goats and calves

In order to determine the usefulness of the goat as a model host for Ostertagia ostertagi, a series of experiments was conducted in which young goats and calves were experimentally infected with L3 of calf-source and goat-source isolates. The goat-source isolate was derived from a continuous passage of the bovine parasite in goats. Patent infections resulted in 73 out of 86 inoculated goats (85%). The largest number of patent infections was observed when inoculation consisted of a single dose of goat-source larvae. Percent establishment of infection was generally low in goats inoculated with either larval source. Time taken to achieve patency in goats was frequently within the range normal for cattle infections, but was often extended (21-67 days). With the exception of the generally higher level of establishment of goat- or calf-source isolates in calves and the low frequency of the vulval flap in adult female worms established in goats, little difference was observed in percent establishment or worm population characteristics of the two isolates in goats as based on source of larval inoculum, inoculation course, and age of host at inoculation. Prolonged passage of infection in goats did not result in stabilized isolate more adapted to the goat or less adapted to calves. Fecal egg counts were generally minimal or negative in goats during the first 30 days of infection, but were often increased and not substantially lower than counts in calf infections after 60 or 90 days. Low level egg counts in goats were observed to persist for up to 17 months. During the spring of 2 years, goat kids grazed on a cattle pasture acquired O. ostertagi infections which included adult worms, but a larger number of early L4. The latter were presumed to be inhibited in development just as such inhibition occurs in cattle during spring.     

Nematodirus battus infection in calves

In studies on the control of parasitic gastroenteritis in calves and sheep, involving an annual rotation of pastures grazed by these host species, it was shown that young cattle could play an important role in the epidemiology of Nematodirus battus, a species usually regarded as a parasite of lambs. Thus, young cattle readily acquired heavy burdens of N battus in spring and the contamination of pastures with eggs from these infections resulted in significant populations of larvae on the herbage, which were infective to both calves and lambs grazed on these pastures in the following year. Although the majority of the N battus eggs hatched in the spring, some hatched in the autumn. The calves developed a strong immunity to N battus during the grazing season as demonstrated by the absence of worms at necropsy in the autumn, despite the presence of infective larvae on the pasture.     

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.     

Interactions between lungworms and gastrointestinal worms in calves

Interactions between gastrointestinal worms (Ostertagia ostertagi, Cooperia oncophora) and lungworms (Dictyocaulus viviparus) in calves were studied by assessing the effect of primary infections with either group of worms on the development of homologous or heterologous challenge infections. Primary infections with lungworms resulted in some degree of resistance to challenge with gastrointestinal worms, but this resistance was lower than that found after homologous infection. Primary infections with gastrointestinal worms did not confer any resistance to challenge with lungworms. On the contrary, an indication was found of some enhancing effect of previous gastrointestinal worm infection on the establishment of lungworms. The highest degree of resistance against lungworm challenge was found where calves have been primarily infected with lungworms. Lungworm infections produced some elevation of serum pepsinogen levels. Gastrointestinal worms evoked a rise in circulating eosinophils, although this rise was smaller and occurred later than in lungworm-infected calves. Under the conditions of the experiment, the effect of 6000 infective lungworm larvae on weight gain was larger than the effect of 100,000 L3 of Ostertagia ostertagi and 100,000 L3 of Cooperia oncophora.     

The significane of Nematodirus helvetianus eggs which have survived on a pasture throughout the winter in the transmission of infection to calves.

A field experiment was carried out to determine the significance of Nematodirus helvetianus eggs which had survived throughout the winter in the transmission of infection to calves turned on to a pasture in the early summer. The calves became infected but did not exhibit symptoms of clinical disease. It was concluded that eggs which survive the winter are unlikely to be associated with outbreaks of disease.     

Grazing study in Ireland using the morantel sustained release bolus for controlling nematodiasis in calves

The morantel sustained release bolus was administered at turnout to first-season grazing calves in order to assess its efficacy in the seasonal control of infection by nematode parasites in Ireland. The pastures grazed by control calves showed a marked increase in gastrointestinal trichostrongylid infective larvae by September, while numbers of infective larvae on pasture grazed by bolus-treated calves remained at a low level throughout the grazing season. In consequence, the controls showed significantly higher worm egg counts in late season and significantly higher worm burdens (mainly Ostertagia spp) at necropsy carried out in November on representative number of principal animals selected from each group. These reduced worm burdens were attributed to the suppression of egg output during the early part of the season as a result of treatment with the morantel sustained release bolus at turnout in the spring. Pasture contamination with Dictyocaulus viviparus larvae was present on all treatment pastures. The bolus-treated calves however were subjected to an increase in D. viviparus infection which occurred on their pasture in late season after the active life of the bolus had expired. It was concluded that bolus treatment delayed (rather than prevented) the buildup of D. viviparus infection on the pasture by 60-90 days.     

Strategic anthelmintic treatment of young cattle during summer in a Mediterranean-type climatic environment

A worm-control program utilising treatment of young grazing cattle with fenbendazole on two occasions during summer was tested in the Mediterranean-type climatic environment of south-west Western Australia. The grazing system aimed to produce steers by introducing three-month-old weaned calves to pasture in mid-winter until they were sold in early summer. Comparisons were made of the numbers of worm eggs passed on to plots by treated and untreated animals during autumn, the performances of treated and untreated cattle and the performances of calves introduced to the plots in mid-winter. The “tracer” calf technique was used to determine the availability of infective larvae on one untreated and one treated plot for each of the two years of the experiment.Treated animals deposited less Ostertagia spp. eggs on to pasture during autumn than did untreated animals in one of the two years. In both years they deposited less eggs of worm species other than Ostertagia spp. Less intestinal worms were acquired by “tracer” calves grazing treatment plots than those grazing no-treatment plots in both years, but there were no differences in the number of abomasal worms acquired.The reduction in availability of infective larvae of intestinal worms was insufficient to prevent the occurrence of parasitic gastroenteritis in calves introduced to the plots in mid-winter. The fenbendazole treatments did not confer any immediate body-weight advantage on treated animals.On both treatment and no-treatment plots, there were few infective larvae available to grazing cattle during early autumn, there was a rapid attainment of peak availability in winter and then a decline to low availability by mid-spring. In one year, infective larvae of intestinal worms (almost exclusively Cooperia spp.) increased in availability again in late spring and early summer. A high proportion of retarded worms was never a feature of the worm counts of “tracer” calves.It was concluded that the treatments may have been more effective had they been given during autumn.     

The Effects of Age and Previous Infection on the Development of Gastrointestinal Parasitism in Cattle

An age resistance in cattle to establishment of infection with Cooperia oncophora was not demonstrated. Cattle exposed to a heavy infection for the first time at approximately 15 months of age were as susceptible to establishment of infection as 3 to 4 month old calves, but stunting of worms and inhibition of ovulation did occur in the older animals, possibly due to a rapid development of resistance as a result of sensitization by a previous extremely light infection.

An age resistance in cattle to infection with Nematordirus helvetianus was not clearly demonstrated. At necropsy, 8 of 9 calves and 2 of 6 yearlings exposed to pasture infections for the first time did harbour Nematodirus worm burdens, while yearlings which were heavily infected previously were completely free of this species.

Under the conditions of this investigation, age and acquired resistance to Ostertagia ostertagi were not demonstrated, since previously non-exposed calves and yearlings and previously infected yearlings had comparable worm burdens.

This study demonstrated the adverse effect that heavy parasitism has on the development of susceptible animals. Animals which had little or no exposure to parasitism were found to be much more susceptible to the effects of parasites than were resistant animals.

     

Efficacy of morantel against nematode populations in calves exposed on a pasture stocked for two years with morantel sustained-release bolus-treated calves

Two groups of 10 parasite-free calves were maintained either for 2 weeks on a pasture grazed by nonmedicated cattle (pasture A) or for 3 weeks on a pasture grazed by morantel sustained-release bolus-treated cattle (pasture B) for the preceding 2 years. After a 4-week holding period to allow for maturation of acquired gastrointestinal nematodes, 5 calves from each group were administered a therapeutic dose (10 mg/kg of body weight) of morantel tartrate. All calves were necropsied 1 week later, and the abomasal and small intestinal nematodes were isolated, identified, and enumerated. A comparison of efficacies between nonmedicated and morantel tartrate-treated calves of each pasture demonstrated that morantel was equally effective against the gastrointestinal nematode infections, regardless of infection source (ie, pasture A vs pasture B). The overall nematode reductions due to morantel tartrate treatment of calves that grazed pastures A and B were 98% and 96%, respectively. It was concluded that the sensitivity of gastrointestinal nematodes to morantel tartrate was not diminished in calves maintained on pasture B, which had been stocked with morantel sustained-release bolus-treated calves for the preceding 2 grazing seasons.     

Experimental and natural infection of calves with Bunostomum phlebotomum

An experiment was conducted to determine the efficiency of a method of experimental infection of weaner beef calves with Bunostomum phlebotomum and to compare such infection with that established by natural infection. Six calves, maintained on a concrete-floored pen, were inoculated with B. phlebotomum L3 by placing the larval inocuulum, in small volume, in the outer chamber of the ear while the animal was restrained for 18 min. Inoculation doses of 20, 30, 40, 50, 60, and 80 thousand L3 were used. Six other calves were grazed on pasture known to be heavily contaminated with hookworm. All animals were killed 72 days after experimental infection and 93 days after initial exposure to pasture infection. The experimental and naturally-infected calves became patent at 55 and 66 days, respectively, after exposure to L3. Red blood cell counts and hemoglobin values were markedly depressed in both groups and lowest values coincided with onset of patency. There was difference in liveweight changes, but both groups lost weight during the prepatent period of infection and gained weight with the onset of patency. The largest number of hookworms was established at the 30000 L3 inoculation level; little or no establishment was observed at the 2 highest levels. Sizeable adult hookworm burdens were established in 4 out of 6 pastured calves. Intestinal pathology was generally more severe in experimentally-infected calves, consisting of a thickened mucosa and masses of punctate, hemorrhagic foci. Pastured calves also acquired large burdens of Ostertagia ostertagi, particularly inhibited early fourth-stage larvae. Moderate to severe abomasal pathology and elevated plasma pepsinogen were associated with ostertagiasis in the pastured calves. The experimental infection method is efficient in establishing high levels of B. phlebotomum infection in calves currently or previously infected with other gastrointestinal nematodes.     

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)     

Faecal excretion of Salmonella hadar from calves grazed on pastures fertilised with S. hadar-contaminated broiler litter

The risk of Salmonella hadar infection in weaned calves grazed on pasture artificially contaminated with the organism via broiler litter applied at commercial dressing rates was assessed. A group of four calves was grazed on artificially contaminated pasture and a control group was grazed on an adjacent identical paddock. A ninth calf was given S. hadar together with an anthelmintic drench, and a tenth was fed on a mixture of contaminated broiler litter and hay for 36 hours. Rectal swabs were collected from the calves at weekly intervals and examined for the presence of salmonellae. Two of the calves in the group on contaminated pasture and both the control positive calves shed S. hadar in their faeces on at least one occasion. The S. hadar contamination was detectable on the pasture for at least 42 days after application of the contaminated litter.     

On the Natural Seeding of Marshland Pastures with Bovine Gastrointestinal Parasites

By placing parasite-free calves in paddocks grazed by infected animals for 18 day periods at various times during the previous season it was shown that eggs of Ostertagia ostertagi, Cooperia oncophora and Nematodirus helvetianus deposited on pastures from early July to October of one year were able to survive in the Maritime area of Canada over winter either as eggs and/or larvae and contribute to residual infections on these pastures the following spring. The greatest deposition and/or survival of those eggs that were shed on pasture occurred in August and September for Cooperia and in September and October for Ostertagia. Greatest deposition of Nematodirus occurred in July and August and relatively few Nematodirus eggs shed in late September or early October were infective early in the next season.

The number of generations of worms per year was low, ranging from one to two or perhaps three per year depending on the species. There was a delay in the maturation of many worm eggs.

Residual overwintering infections play a significant role in the establishment of initial infections each summer in susceptible stock. These animals recontaminate the pastures leading to the subsequent development of large numbers of infective larvae by late summer and autumn.

     

Metabolism and growth in housed calves given a morantel sustained release bolus and exposed to natural trichostrongyle infection

Three groups of calves, previously grazed on permanent pastures contaminated with bovine trichostrongyle (Ostertagia and Cooperia species) infective larvae, were housed from October to May. During the grazing season one group had received fenbendazole at fortnightly intervals to suppress trichostrongyle infections, one received a morantel sustained release bolus before grazing to limit trichostrongyle contamination of the pasture, and the control group was only medicated when heavy infections caused clinical type 1 ostertagiasis. Digestibility of the whole diet was poorer in the control cattle, particularly for dry matter, crude protein and energy fractions. Balance studies conducted throughout the winter housed period showed that both increased faecal and urinary nitrogen outputs in the control animals contributed to a significantly reduced overall nitrogen retention. The effects were most apparent during clinical type 2 ostertagiasis, which occurred in March in the control group.     

Bovine Dictyocaulosis: Pattern of Infection and the Prevention of Parasitic Bronchitis

A combined epidemiology and control investigation was performed with parasite-free calves turned out in May on a permanent pasture naturally contaminated with lungworm larvae the previous year. Before the start the field was divided into two plots. One plot was grazed by 12 calves after the first week of May. The other plot was grazed by 12 calves turned out two weeks later. Both groups as well as the plots grazed by them were subdivided six weeks after turning out. Based on a predicted rise in the pasture larval contamination with infective lungworm larvae, one subgroup of each main group was given a tactical anthelmintic treatment six weeks and again eight weeks after their date of turning out. Patent infections from overwintered larvae were detected in both main groups after four weeks of grazing, but not in all individuals of the late turned-out group. The excreted larvae gave rise to pathogenic pasture larval contaminations on the two initial plots five to six weeks after turning out. In the control groups, early turning-out resulted in approx. 10 times higher larval recoveries in faeces and pasture compared to late turning-out. Seven to eight weeks after turning-out critical, severe parasitic bronchitis had developed in the early turned-out control group. In the late turned-out controls, clinical signs were obvious but not critical. Outbreaks were not observed in any of the experimental subgroups, and no larval excretion was observed among them within four to five weeks following treatments. Similarly, no larvae were recovered from their pastures two weeks after treatment and onwards. A third treatment was given to both experimental groups on the same date (August 21) to suppress gastrointestinal parasitism. However, the level of this infection, appeared moderate, probably due to comparatively low precipitation and extensive supplementary feeding given in late summer to compensate for scarcity of grass.     

Control of gastrointestinal nematodes in first season grazing calves by two strategic treatments with eprinomectin

A study was carried out to evaluate the effects of strategic early-season treatments with eprinomectin on first-season grazing calves exposed to strongyle infections on a naturally contaminated pasture. Two groups of first grazing season (FGS) calves were turned out in mid-May on two plots that were similar with respect to size and herbage infectivity. They grazed separately until housing at the end of October. One of these groups was given eprinomectin pour-on at turnout and 8 weeks later, while the other group served as untreated controls. The results showed that the treatments reduced gastrointestinal strongyle infections throughout the season as evidenced by lower faecal egg counts and serum pepsinogen levels compared with the controls. Furthermore, the results of herbage larval counts and postmortem worm counts in tracer animals demonstrated that the treatment had reduced herbage infectivity on the 'treated' plot. Finally, the chemoprophylactically treated calves had a better weight gain over the duration of the study than the untreated controls.