Seasonal pattern of inhibition of Ostertagia ostertagi in calves in northeast Mississippi

The composition of, and seasonal changes in, populations of gastrointestinal parasites of calves in northeast Mississippi were determined for 10 months post-weaning. After weaning on 15 October, 20 mixed breed beef steers were grazed together on a 4 ha fescue/bermudagrass pasture. From November through August of the following year, two of the calves were removed each month for necropsy and counting of gastrointestinal nematodes. Eight species of worms were found: Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, Bunostomum phlebotomum, Cooperia spp., Trichostrongylus colubriformis, Oesophagostomum spp., and Trichuris ovis. During all months, Ostertagia ostertagi and Cooperia spp. combined comprised at least 89% of gastrointestinal nematode burdens. Cooperia spp. represented 92.6% of the total worm burden of calves in November but declined to about 56% in January and February. From March through August, Ostertagia ostertagi comprised at least 79% of the worms from calves. Numbers of inhibited Ostertagia ostertagi increased markedly from February to March and remained at high levels prior to resumption of development in August. The proportion of Trichostrongylus axei remained about 4% throughout the year, but the highest numbers were recorded in the summer months. Other species were minor components of the worm population. These data indicate that with respect to Ostertagia ostertagi, northeast Mississippi can be considered a summer inhibition zone.     

Cellular and chemical mediators of type 1 hypersensitivity in calves infected with Ostertagia ostertagi: histamine, prostaglandin D2, prostaglandin E2 and leukotriene C4

Plasma histamine, prostaglandin E2 (PG) D2, PGE2, and leukotriene (LT) C4 levels were determined in 26 Holstein steers before and after natural or experimental infection with Ostertagia ostertagi. Post-infection abomasal lymph was also assayed for PGD2, PGE2, and LTC4. Histamine determinations were performed on abomasal tissue from three locations. Results showed that: (1) tissue histamine levels increased in steers with type 2 ostertagiosis, (2) lymphatic PGD2 and PGE2 levels were increased, probably as a result of macrophage activity, (3) lymphatic LTC4 levels increased in steers with type 1 ostertagiosis, and were correlated with tissue eosinophilia, and (4) plasma levels of PGD2, PGE2, LTC4 and histamine were not useful for predicting worm burdens. These findings suggest a functional role for eosinophils and mast cells in the pathophysiology of ostertagiosis, through mediation of a type 1 hypersensitivity reaction.     

Acquired immunity against Cooperia spp. and Ostertagia spp. in calves: effect of level of exposure and timing of the midsummer increase

In two experiments, groups of calves were exposed to different levels and patterns of infection with Ostertagia spp. and Cooperia spp. The experimental design simulated the stereotypic pattern of herbage infestation, including both as normal and a delayed midsummer increase, under conditions of set-stocking. After this simulated 'first grazing season', calves were followed during the subsequent winter housing. At the end of that housing period some calves were challenged with 100,000 L3 Cooperia spp. and 40,000 L3 Ostertagia spp. and slaughtered 23 days later. All previously infected calves were protected against the establishment of the challenge infection with Cooperia spp., but not against Ostertagia spp. For the latter a significant negative correlation was found between worm count and previous level of exposure to infection. During the simulated first grazing season, changes in the ratio of Cooperia to Ostertagia eggs in the faecal egg output and the genus-specific egg count were influenced by both the level of exposure and the timing of the midsummer increase. It is concluded that acquired immunity against both parasite genera develops depending on the level of exposure to infection during a first grazing season, and that delaying the midsummer increase results in a delay of the acquisition of an effective immunity as measured by faecal egg counts and the ratio of Cooperia to Ostertagia egg output.     

Performance, digestion, and mastication efficiency of Holstein steers fed whole or processed corn in limit- or full-fed growing-finishing systems

We conducted two trials to examine the effects of restricted vs full feeding and of grain processing method on feedlot performance, digestion, and mastication efficiency by Holstein steers in different growing-finishing systems. In Trial 1, 272 Holstein steers (177 +/- 9.98 kg) were blocked by weight and assigned to growing phase diets based on corn silage (SIL), steam-flaked corn that was either limit-fed (SFLF) or full-fed (SFFF), or whole corn that was limit-fed (WCLF) or full-fed (WCFF). Limit-fed steers were fed at levels predicted to allow daily gain of 1 kg/d. On d 112, all steers were switched to WCFF or SFFF diets until the mean BW of each treatment group was 545 kg. Overall, steers fed WCLF and SFLF during the growing phase and finished on SF were 8.1 and 6.6% more efficient at converting dietary ME to gain (P = .02 and .04, respectively) than steers in the SFFF group. In Trial 2, three ruminally and duodenally cannulated Holstein steers were fed whole (WC) and rolled corn (RC) diets at FF and LF intake in an incomplete replicated 2 x 2 switchback design. Ad libitum access to feed resulted in higher (P = .02) ruminal starch digestibility than did limit-feeding, and calves had higher total tract DM (P = .05) and starch (P = .03) digestion at the heavier BW. Limit-feeding whole corn resulted in increased particle size of masticate (P = .06) compared with full-feeding whole corn. Because of apparent differences in mastication efficiency between limit-fed and full-fed calves, grain processing method during periods of restriction and compensatory growth may be important considerations for managing growth in systems that incorporate limit-feeding.     

Differential pattern of c-fos mRNA in rat brain following central and systemic administration of interleukin-1-beta: implications for mechanism of action

The epidemiology of gastrointestinal nematodes was studied in a spring calving herd in northeast Mississippi. Pregnant, mixed breed beef cows (n = 15) were placed on a 10 ha fescue/bermuda grass pasture from January 1990-February 1992. In both years, calves were born from February-April and were weaned and removed from the pasture in mid-October. Fecal egg counts (EPG) and generic composition of nematodes in fecal cultures were determined monthly for cows and calves. Estimation of numbers of third-stage larvae on herbage also was determined monthly from March 1990-February 1992. Worm-free tracer calves (2-3 per month) were allowed to graze for 1 month periods and slaughtered for counting and identification of gastrointestinal nematodes. The mean monthly EPG of cows was consistently low (0.23-3.41); EPG of calves increased from spring through fall of both years. Five nematode genera were identified from fecal cultures of cows and calves. Ostertagia and Trichostrongylus spp. were the predominant nematodes in cows, while Ostertagia and Cooperia spp. were predominant in calves. Numbers of third-stage larvae on herbage declined from spring through summer and remained at low levels until late fall/winter, when numbers increased markedly. Eleven nematode species were identified from tracers, but O. ostertagi and Cooperia spp. predominated in most months. Seasonal changes in tracer worm counts coincided with similar changes in counts of third-stage larvae on herbage. Inhibition of O. ostertagi occurred in tracer calves during spring, but did not give rise to a marked increase in egg production in cows during fall.     

Prevalence and epidemiology of trichostrongylids in Wyoming cattle with consideration of the inhibited development of Ostertagia ostertagi

During 1988, monthly collections of abomasa and the cranial portion of the small intestine of 208 native Wyoming cattle were examined for adult and larval helminth parasites. Egg counts were performed on colonic faecal specimens. The animals ranged from 7 months to 8 years of age and were sampled at slaughter houses or diagnostic laboratories from five different counties in the State. Most of the cattle had ranged for a long time on non-irrigated, high altitude grass plains from about 1250 to 2500 m above sea level. All animals examined were found infected. Nematode genera (and number of species) found included Ostertagia (4), Trichostrongylus (2), Haemonchus (1), Cooperia (4) and Nematodirus (2). One trematode, Fasciola hepatica, and a cestode, Moniezia benedeni, also were found. Trichostrongylus axei, Trichostrongylus longispicularis and Cooperia lyrata were found for the first time in Wyoming, Ostertagia circumcincta was found for the first time in cattle in Wyoming, and Haemonchus placei, tentatively identified in a previous survey, was definitively confirmed. Predominant species (and prevalence) were Ostertagia ostertagi (98%), Cooperia oncophora (60.6%), Ostertagia bisonis (41.8%), Cooperia bisonis (33.6%) and T. Axei (27.9%). One or more of the four species of Ostertagia were found in all animals. Inhibited O. ostertagi and O. bisonis larvae predominated from November to April and reached a peak in January to comprise 88% of the total nematode burden for that month. The adult population of abomasal nematodes peaked in April and predominated thereafter until October. Haemonchus placei also spent the autumn-winter period in an inhibited state of development. Faecal egg counts were lowest during winter months, when the highest number of worms were present as L4 larvae, as determined by luminal and mucosal counts. Nematode populations in the small intestine peaked in June and persisted until November. The results of this study showed the magnitude and species composition of nematode parasitism in cattle raised on high altitude grass plains, underscored the inaccuracy of faecal egg counts as an indicator of worm burden during fall and winter seasons, and provided information on which anthelmintic treatment timing would be most efficacious.     

Parasite spectrum and seasonal epidemiology of gastrointestinal nematodes of small ruminants in The Gambia

One hundred and four post mortem examinations of randomly selected sheep (52) and goats (52) were carried out weekly from March 1990 to February 1991. Gastrointestinal parasites were identified and counted. A large spectrum of 16 helminth species was found in 101 (97%) infected animals. The nematodes infecting small ruminants were, in order of predominance: Trichostrongylus colubriformis (96% of all animals), Oesophagostomum columbianum (82%), Haemonchus contortus (67%), Strongyloides papillosus (55%), Gaigeria pachyscelis (38%), Cooperia spp. (49%) and Trichuris ovis (12%). Forty-five (43%) necropsies revealed an infection with Moniezia benedeni, Avitellina centripunctata or Stilesia globulosa. Infections with Schistosoma bovis and Paramphistomum spp. were rarely seen. Goats carried significantly lower worm burdens than sheep and were less often infected by tapeworms. Nematode worm burdens followed a similar seasonal pattern in both host species. While Trichostrongylus colubriformis was also recovered in high numbers in the mid dry season, other species such as H. contortus, Strongyloides papillosus and Oesophagostomum columbianum reached distinct peaks in the rainy season (July-October). Different survival strategies for the prolonged dry season were observed. Haemonchus contortus outlived the unfavourable climatic conditions as inhibited larvae in the abomasal mucosa, while the other nematode species survived as adults with a reduced fecundity. Egg production per adult worm specimen was found to depend heavily on the season and egg counts in the dry season (November-June) did not correspond to the size of worm burdens. Unexpectedly high worm burdens were recovered from adult and old animals. Investigations of young animals indicated that no reinfection can occur during the dry season. The findings are discussed with regard to their relevance for strategic control of gastrointestinal nematodes in small ruminants.     

In vitro dog detrusor strip contractile responses and calcium ion activity

An attempt was made to immunise lambs by the intra-muscular injection of concentrated metabolites obtained from the in vitro culture of Ostertagia circumcincta, by the oral administration of lyophilised metabolites or by the subcutaneous injection of living third, fourth and fifth stage worms grown in vitro. Protection appeared to have been elicited by each treatment as the worm burdens, the lengths of the worms and the faecal worm egg counts in the immunised lambs were less than those of the control lambs.     

Population dynamics of the parasitic stages of Oesophagostomum dentatum in pigs in single and trickle infections

A mathematical model was developed to describe the dynamics of the parasitic stages of Oesophagostomum dentatum in pigs. An immigration-death model with constant establishment, development and death rates was fitted to L3, L4 and adult worm burdens observed in a single-infection experiment. Female worm length was modelled by a function of worm age and total worm burden, while worm egg production (eggs per gram faeces per female worm) was modelled by a function of worm age and worm length. The model was then used to predict worm burdens observed in a trickle-infection experiment. The predicted worm burdens were much higher than those observed, suggesting that worm death rates were higher during the trickle infection. After increasing worm death rates to fit the observed worm burdens, female worm lengths and egg production in the trickle infection were predicted. At the medium- and high-dose rates, predicted worm lengths and, thus, egg production were lower than observed, while at the low-dose rate predicted egg production was too high. It appeared that in the trickle infections, total worm burden had less influence on observed female worm length and egg production than in the single infections. The results suggest that the demography of O. dentatum in pigs differs between single and trickle infections.     

Collaborative problem-solving in telemedicine and evidence interpretation in a complex clinical case

The objective of this study was to evaluate the effect of different infection levels of Ostertagia ostertagi and Cooperia oncophora in a simulated 'first grazing season' on the resistance of calves to an artificial challenge infection. The infection levels were determined by the infection schedules and the chemoprophylaxis used. Thirty six 7-11-month old Holstein-Friesian bull calves were randomly divided into four groups. The animals of group B received an ivermectin sustained release bolus (ISRB) on day 0. The calves of group D were treated on days 0 and 56 with a subcutaneous injection of doramectin (0.2 mg kg(-1) BW). Group C was the untreated control group. The calves of group N were used as helminth-naive controls, while the animals of groups B, C and D were trickle infected for 24 weeks. The infection schedules were designed to simulate the expected infection pattern for each treatment group under set-stocked conditions in temperate climate areas. After the last infection, all animals were treated with oxfendazole. One week later, all animals received a challenge infection of 50,000 O. ostertagi L3 and 100,000 C. oncophora L3, spread over 10 consecutive days. During the primary infection period the faecal egg output and the serum pepsinogen and antibody levels reflected the different levels of host-parasite contact between the groups (group C > group D > group B > group N). After the challenge infection, faecal egg counts, total Ostertagia burden, size of the adult worms and abomasal globule leucocyte counts all indicated a positive relationship between the level of Ostertagia infection during the primary infection period and the level of acquired resistance. A reduction of host-parasite contact during the primary infection period, as a consequence of the infection schedule and the chemoprophylaxis used, resulted in a diminished level of resistance to the artificial challenge infection with O. ostertagi. Faecal cultures and small intestine worm counts indicated that all previously infected groups had acquired a high degree of resistance to the Cooperia challenge infection.     

Helminth species of goats in Germany

The helminth fauna of the gastrointestinal tract of 25 and the respiratory organs and the livers of 6 German goats was qualitatively and quantitatively examined. One trematode species (Dicrocoelium dendriticum), 2 species of cestodes (Moniezia expansa and metacestodes of Taenia hydatigena) and 28 species of nematodes (24 in the gastrointestinal tract and 4 in the lungs) were recorded. Two goats were infested with Oestrus ovis larvae. The most prevalent species were Ostertagia circumcincta and Chabertia ovina (84% each), Ostertagia trifurcata and Oesophagostomum venulosum (76% each), Ostertagia pinnata and Trichostrongylus colubriformis (64% each), Trichuris ovis (60%) and Skrjabinema ovis and Trichuris globulosa (56% each). The highest mean worm counts were seen in goats infected with Skjabinema ovis (4003), Ostertagia circumcincta (2501), Trichostrongylus axei (1825), Trichostrongylus colubriformis (1578) and Nematodirus battus (1050). Totally, the goats did harbour more nematodes in the abomasum (3734) than in the small intestine (1707) or the large intestine (2343). The lungs were parasitized by Cystocaulus ocreatus, Muellerius capillaris, Neostrongylus linearis and Protostrongylus rufescens.     

Evaluation of olfactory and auditory system effects of the antihyperthyroid drug carbimazole in the Long-Evans rat

Groups of lambs either with or without controlled-release albendazole (ABZ) capsules (CRCs) were challenged twice weekly for 6 weeks with either drug-susceptible or drug-resistant Ostertagia circumcincta and Trichostrongylus colubriformis. Groups with and without CRCs remained unchallenged as controls. There was minimal establishment of drug-susceptible parasites of either species in those lambs with CRCs. However, drug-resistant parasites of both species established adult worm burdens in the presence of the capsules. The humoral immune response, as measured by the serum antilarval (L3) antibody (Ab) titre, was pooled for weeks 4-6 and compared for each group. With the exception of anti-T. colubriformis Ab in group 2, anti-L3 Ab titres were significantly higher in all the parasite-challenged groups as compared to the control animals. Also, with the exception of anti-resistant O. circumcincta Ab levels in the CRC-treated animals (group 5), no significant difference was observed in Ab titres between the four groups challenged with either resistant or susceptible larvae. The results demonstrate the inability of CRCs to prevent establishment of drug-resistant parasites and that immune stimulation is not inhibited by the capsules.     

Evaluation of the clinical impact of endoscopic ultrasonography in gastrointestinal disease

A total of 120 gastro-intestinal tracts and 960 faecal samples were examined to assess the prevalence and seasonal changes in the gastro-intestinal helminth parasites of Red Sokoto (maradi) goats slaughtered at Ibadan between May 1991 and April 1992. Egg types of strongyles, Strongyloides, Trichuris, Skrjabinema, Dicrocoelium and Moniezia were encountered in 93%, 83%, 44%, 0.9%, 2.3% and 31% of the faecal samples respectively. However, only strongyle, Strongyloides and Trichuris eggs occurred in large numbers and were more common during the rainy season than in the dry season. The parasites recorded and their prevalences were Haemonchus contortus (90.0%), H. ovis (5.0%), Strongyloides papillosus (80.8%), Trichostrongylus colubriformis (78.3%), T. axei (69.2%), Trichuris ovis (72.5%), T. globulosa (38.3%), Oesophagostomum columbianum (67.5%), Cooperia curticei (58.3%) Gaigeria pachyscelis (40.8%), Skrjabinema ovis (5.0%), Nematodirus battus (5.8%), Moniezia expansa (29.2%), M. benedeni (10.0%), Paramphistomum spp. (5.0%) and Cysticercus tenuicollis (33.3%). Haemonchus ovis is reported for the first time in Nigeria. Mixed infections were most prevalent. Young goats were more commonly infected and had higher worm counts than adult goats. Only Haemonchus, Trichostrongylus, Strongyloides and Cooperia spp. occurred in large numbers. Irrespective of the age of the goats, higher worm counts were generally encountered during the rainy season than in the dry season. The results are discussed in relation to the control of helminthiasis in grazing animals in Nigeria.     

Experimental cyathostome challenge of ponies maintained with or without benefit of daily pyrantel tartrate feed additive: comparison of parasite burdens, immunity and colonic pathology

Eighteen mixed-breed, naturally infected ponies ranging in age from 1 to 16 yr and four cyathostome-na?ve ponies reared and maintained under parasite-free conditions ranging in age from 1 to 4 yr were used in this study. Naturally-infected ponies were treated with 1 dose of ivermectin (IVM) at 200 micrograms kg-1, followed by a 5-day regimen of oxibendazole (OBZ) at 20 mg kg-1 to remove existing cyathostome burdens; cyathostome-na?ve control ponies were treated with IVM alone. The naturally infected ponies were matched on age and gender, then randomly assigned to one of three treatment groups of six animals per group; the four cyathostome-na?ve ponies constituted a fourth group. Following OBZ treatment, Group 1 ponies were treated with pyrantel tartrate (PT) in their pelleted ration; the remaining ponies received only the pelleted ration. Beginning on experiment Day 3, a daily challenge infection of 10(4) mixed cyathostome larvae was administered orally to ponies of Group 1, Group 2 and the cyathostome-na?ve controls. Group 3 ponies served as unchallenged controls to determine residual parasite burdens following IVM/OBZ treatment. Necropsy examinations were performed on three Group 3 ponies on Day 1; the remainder of the necropsy examinations began on Day 41. Cyathostome burdens were evaluated by recovery of larvae and adults from the luminal contents, by digestions of the intestinal mucosa, and by mural transillumination of full-thickness intestinal sections. Differences in postchallenge clinical responses were also compared. Necropsy examinations included comparisons of grossly visible inflammation of the large bowel, weights of biopsy specimens from each region, and histologic evaluations of these biopsies. Parasite recoveries at necropsy indicated a strong protective effect derived from daily PT treatment. Mean weights of intestinal biopsies corresponded with worm burdens, but histological evaluation did not reveal architectural or cellular changes to account for the increase in weight; therefore, edema was suspected. A strong age-related resistance to challenge infection was apparent in both the PT-treated and control groups by virtue of the lower mean worm burdens found in older ponies compared to younger ponies of the same treatment group; however, daily PT treatment of older ponies reduced the variability of their worm burdens to a uniformly low level. Comparisons of luminal and mucosal parasite burdens of age stratified nontreated controls further suggest that the age related resistance, which is acquired, targets increasing numbers of parasite stages as this resistance matures. Further, there is no evidence for an immune mediated acquisition of hypobiotic L3.     

Response of cattle treated with a fenbendazole slow release bolus to challenge from nematodes the following season

Nematode infection of cattle treated in their first year at pasture with the fenbendazole slow release bolus ('Bolus group') was compared during the second year with that of untreated cattle. Ostertagia was the most prevalent parasite associated with Cooperia. Except for the Dictyocaulus spp. which caused clinical signs of bronchitis in the 'Bolus' group, the infection during the second year resulted in a moderate response of the cattle whatever the group. Rises in both pepsinogen and gastrin levels were correlated with the number of Ostertagia L3 on herbage. Damages in the abomasal mucosa were more frequent and severe in the 'Bolus' group where more inflammatory signs were observed in spite of a smaller number of worms. Nevertheless, the differences in total weight gains were not significant thanks to a compensatory effect during the second part of the grazing season in the 'Bolus' group. Hypotheses related to a minimum threshold of infection during the first year necessary to develop high enough protection during the second year are discussed. The pathological effects of gastrointestinal nematodes seem to vary more according to the inflammatory response than to the number of worms.     

The determination at housing of exposure to gastrointestinal nematode infections in first-grazing season calves

Various parameter estimates were assessed at housing in calves that had been exposed to gastrointestinal nematodes during a first grazing season. The analysis involved 41 groups of first grazing season (FGS) calves on 15 different farms in Belgium and comprised groups that had received chemoprophylactic treatment and untreated controls. Serum pepsinogen levels gave the clearest division between chemoprophylactic-treated calf groups (all were <2.6 U tyr), and untreated calf groups in which sub-clinical (range: 2.0-4.1 U tyr) and clinical infections (range 3.7-6.3 U tyr) occurred. There was also a tight relationship between individual pepsinogen values and adult Ostertagia burdens obtained at slaughter. In chemoprophylactic-treated groups there was a significant negative relationship between mean serum pepsinogen levels at housing and the proportion of the grazing season covered by different chemoprophylactic systems. Although only limited data on crude adult Ostertagia antigen ELISA were available, a good relationship between optical densities and estimated exposure was also found. The parasitological parameters, faecal egg counts and pasture Ostertagia larval counts at housing, and weight gain per day, gave less clear divisions among the three categories (chemoprophylaxis, sub-clinical and clinical). Distinguishing how much exposure a calf group has experienced during a first grazing season could help in designing more appropriate control measures for the FGS calves in the next year, assuring good protection and at the same time allowing sufficient exposure for the development of acquired immunity to Ostertagia, and for this serum pepsinogen is recommended.     

Oesophagostomum spp. in pigs: resistance to reinfection

For a study on the occurrence of resistance to reinfection with porcine nodular worm species, pigs were infected twice weekly with 1,000 infective larvae (L3) of Oesophagostomum quadrispinulatum for 8 weeks. All pigs, including noninfected controls, were then treated with fenbendazole. At 10 days after treatment, all pigs received a single challenge inoculation of 5,000 L3 of either O. dentatum or O. quadrispinulatum, respectively. Pigs were slaughtered at 6 weeks after the challenge infection for determination of their worm burdens. The pigs trickle- and challenge-infected with O. quadrispinulatum had significantly lower egg excretion levels (P < 0.01) and worm burdens (P < 0.05) than challenge control pigs, thus indicating some degree of host immunity against the homologous challenge infection. No resistance to reinfection was evident for the heterologous challenge infection. This study elucidates further aspects of the interaction between nodular worm species in the pig.     

The preventive effect of the fungus Duddingtonia flagrans on trichostrongyle infections of lambs on pasture

Four groups of 8 parasite-naive Dorset-crossbred lambs, 3-4 months old, were turned out on infected pasture on 2 May and allocated to 4 separate paddocks. From May to September, 2 groups received Duddingtonia flagrans (10(6) chlamydospores per kg body weight per lamb per day) mixed in 100 g of barley, while the other 2 groups received barley only. All groups remained set-stocked until slaughter for worm counts on 10 October. In late June, all lambs were treated with fenbendazole due to severe parasitic gastroenteritis in all groups. The faecal egg counts were comparable for the 2 treatments throughout the grazing period. Larval development of Ostertagia/Trichostrongylus spp. in faecal cultures was 1-28% in the fungi-fed groups compared with 60-80% in the untreated groups (P < 0.05). In September, pasture larval counts of Ostertagia/Trichostrongylus were 930 and 4400 L3 kg-1 on paddocks of fungi-fed and untreated groups, respectively. Corresponding figures for Nematodirus spp. were 7200 and 11600 L3 kg-1, respectively. At slaughter, the number of immature Ostertagia spp. was 62% lower in the fungi-fed groups compared with the untreated groups (P < 0.05). Four parasite-free lambs were introduced to each paddock during the period 3-23 October and slaughtered for worm counts after 3 weeks of housing. The total worm burden of tracers on paddocks previously grazed by fungi-fed lambs was reduced 86% (P < 0.05; geometric means) compared with control groups, while significant reductions were also seen in abomasal worm counts (68%; P < 0.05), N. spathiger (98%; P < 0.05) and for N. battus (97%; P < 0.01). It is concluded that dosing sheep with D. flagrans while grazing may limit the build up of pasture contamination in the late grazing season and subsequently limit the intake of larvae in sheep.     

The effect of three distinct sex ratios at two Oesophagostomum dentatum worm population densities

Helminth-free donor pigs were inoculated with infective larvae of Oesophagostomum dentatum. Five weeks later, the donor pigs were killed to recover the adult worms. By nonsurgical rectal transplantation, 6 groups of helminth-free recipient pigs were then given different female-to-male ratios (FMR) of O. dentatum worms (10% females [F], 50% F, 90% F) at either high (300 worms) or low (30 worms) doses. Fecal egg excretions were measured once weekly following transplantation until the pigs were killed 4 wk posttransplantation to assess the worm burdens and their location. There was a strong and significant correlation between numbers of male and female worms located in the different sections of the large intestine, suggesting that the worm sex as well as physiological factors in the pig intestine may govern the location of the worms. There were no significant differences in fecal egg counts or female worm fecundity between any of the groups. However at the low dose level, the female worm fecundity was markedly lower in the L10% F group than in the 2 other groups, thus suggesting for low worm densities an upper threshold for the FMR above which O. dentatum females produce fewer eggs.     

Activity of morantel citrate against strains of benzimidazole-resistant nematodes of sheep in the United Kingdom

The activity of morantel citrate (5.94 mg/kg base) was determined in laboratory tests against field isolates of benzimidazole-resistant nematodes. Its efficacies against adult and seven-day-old worms were 100 per cent and 100 per cent for Cooperia curticei, 95.1 per cent and 69.8 per cent for Haemonchus contortus and 100 per cent and 82 per cent for Ostertagia circumcincta. Morantel citrate was 100 per cent effective against benzimidazole-susceptible Nematodirus battus and Trichostrongylus vitrinus, and it reduced faecal egg counts by 97.9 per cent in sheep infected naturally with benzimidazole-resistant H contortus and O circumcincta.