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The present study used in vitro assays to determine the relative potency of commercial macrocyclic lactone (ML) anthelmintics against larvae of drug-susceptible and drug-resistant Australian isolates of important parasites of sheep and cattle, Haemonchus contortus and Haemonchus placei, respectively. Cattle pour-on products containing abamectin, ivermectin, eprinomectin, doramectin or moxidectin were diluted in DMSO and used in larval development assays. Abamectin was the most potent chemical (lowest IC50 value) towards the drug-susceptible H. contortus Kirby isolate. The abamectin IC50 was approximately 2-fold lower than those for ivermectin, moxidectin, eprinomectin and doramectin. Moxidectin and abamectin were the most potent chemicals towards the resistant H. contortus Wallangra isolate. This isolate showed resistance ratios up to 70-fold towards eprinomectin. The resistance ratio for this species was lowest with moxidectin (ratio of 4.0-fold). Abamectin was also the most potent chemical towards both drug-susceptible (Bremner) and drug-resistant (Dayboro) H. placei isolates. The larval development assay only showed low levels of resistance for the drug-resistant H. placei, with resistance ratios ranging from 1.7 to 2.0 fold for moxidectin and abamectin, up to 3.3-fold for eprinomectin. This study examined the readily-accessible larval life stages of these parasites in in vitro assays, and, hence, the relationship between our findings and relative drug efficacies in vivo remains to be determined. Despite this, the study accords with some evidence from the use of these anthelmintics in the field in demonstrating the potency of moxidectin and abamectin against ML-resistant H. contortus. The study also highlights the usefulness of eprinomectin as a readily-available compound which is a more sensitive marker for ML resistance in in vitro larval development assays than the other commercial ML compounds examined.

The study of the anthelmintic properties of plants rich in plant secondary metabolites can provide ecologically sound methods for the treatment of parasites on grazing animals. The purpose of the present study was to evaluate the anthelmintic effect of five tropical native Australian plant species rich in plant secondary metabolites on adult Haemonchus contortus and Trichostrongylus colubriformis in experimentally infected goats. Thirty young, nematode-free goats were infected with 2500 H. contortus and 5000 T. colubriformis infective larvae thrice weekly for a week (day 1-7 of the experiment). On day 27 after first infection, the goats were allocated into six groups of five animals per group. From day 28 to day 35, fresh leaves from Acacia salicina, Acacia nilotica, Eucalyptus corymbia, Casuarina cunninghamiana and Eucalyptus drepanophylla were included in the goats diet. Five groups were offered leaves from one of these plant species and one group, the untreated control, received only the basal diet formulated with 20% Medicago sativa and 80% Avena sativa. Following plant material administration, the goats were monitored daily until day 40 and then slaughtered on day 41. Total faecal worm egg output, total production of larvae recovered from faecal cultures, total post-mortem worm burdens and the per capita fecundity of female worms were estimated. The toxicity of the plant species for the goats was measured by histopathological analyses of liver and kidney samples. Results showed that goats feeding on the plant material rich in plant secondary metabolites had significantly lower egg output compared to the control goats (P0.05). A similar response was found for larval production in both H. contortus and T. colubriformis supporting that egg output was affected in both species. Although the total worm burdens were not affected by the plant material (P0.05), the per capita fecundity was significantly reduced by E. corymbia, A. nilotica and A. salicina (P0.05). No signs of toxicity were detected in the liver or kidney samples. It is concluded that goats can benefit from the short-term ingestion of plant secondary metabolites, which reduce the total faecal egg output and thus decrease the potential for re-infection from the pasture.

The environmental impact of Duddingtonia flagrans , a potential biological control agent for nematode parasites, was assessed in an improved pasture. Sheep feces containing D. flagrans and feces without D. flagrans were placed on pasture plots on four different occasions (series): May, August, November 1998, and February 1999. At 0, 1, 2, 4, 8, 16, and 24 weeks following fecal deposition, the persistence and dispersal of the fungus from the site of deposition were estimated. In addition, the impact of fungal presence on the numbers of non-target, free-living soil nematodes and microarthropods was assessed. For all four series, D. flagrans was not found outside the point of fecal deposition indicating that D. flagrans had not spread in the horizontal plane. D. flagrans was detected at the point of fecal deposition while intact fecal material was present and persisted for 8–24 weeks after initial contamination in association with the soil under the point of deposition. Over time, there was generally a decline in the number of positive observations of D. flagrans presence and the rate of this decline appeared to be seasonal. D. flagrans was observed in the top 10 cm layer of soil frequently, in the 10–20 cm soil layer occasionally, and in the 20–30 cm soil layer rarely. It is thought that rainfall and the activity of macroarthropods (in particular dung beetles) and earthworms may have contributed to this downward movement through the soil profile. Numbers of free-living soil nematodes and microarthropods at the point of fecal deposition varied considerably between samples but were not reduced by D. flagrans . There were no negative effects of fungal presence on the presence of other nematode-trapping fungi. The results of this study indicate that there were no detectable negative environmental impacts of D. flagrans use in a typical improved pasture.

A series of feeding trials was conducted with penned sheep harboring Trichostrongylus colubriformis infections. They were offered barley grains supporting the growth of the nematophagous fungus Duddingtonia flagrans. It was shown that as little as 5 g of grain/sheep per day was sufficient to virtually eliminate larval numbers from faecal culture. This effect persisted for the time that the fungal grains were fed, and for up to 2 days following cessation of feeding this material. Macerated fungal grains were also incorporated into a range of feed block formulations. In all these, D. flagrans was found to survive the manufacturing process and resulted in significant reductions in larval numbers in faecal cultures set up during the feeding period to sheep. This was observed even for sheep that showed only modest and irregular block consumption. These studies demonstrate that supplementary feeding or block administration offer potential deployment options for D. flagrans as a means of biological control of nematode parasites of livestock.

Merino wether lambs were individually confined and fed a basal diet of oaten chaff containing essential minerals which was untreated or contained 3% urea. Within each dietary group animals were orally infected with either 200 H. contortus (H), 1000 T. colubriformis (T) or both species (H + T) thrice weekly or remained uninfected (C). Weight gain, wool production, and parasite burden were measured over a 19-week period. Sheep on the diet containing urea gained more weight, consumed more feed and grew more wool of higher fibre diameter than their counterparts given no urea. On both diets uninfected sheep consumed more feed than infected sheep and the sheep given no urea and infected with both H and T worm species consumed the least feed. Parasitised sheep gained less weight than uninfected control sheep. Sheep with urea in their diet had lower faecal egg counts when infected with H alone or with H and T but there was no effect of urea on egg count of sheep infected with T alone. In contrast, T numbers after slaughter were reduced in sheep fed diets containing urea whereas H numbers were not affected by diet. It was concluded that supplementation with urea can increase resilience to parasitism thereby improving production and also enhance resistance mechanisms against worms in young sheep on low quality roughage diets. These responses can be partly attributed to stimulation of feed intake, presumably due to enhanced ruminal digestion, but also to elevated rumen NH3–N levels which would be expected to have increased rumen microbial protein synthesis and availability to the intestines.

Nutritional insufficiency and gastrointestinal nematode parasitism are major constraints to small ruminant production in south-east Asia and the Pacific Islands. Research on the effects of low cost supplements which supply nitrogen and essential minerals on the ability of small ruminants to resist infection is summarised. In controlled pen studies in young Merino sheep offered a low quality roughage diet of oaten chaff and essential minerals, supplementation with urea reduced the effects of parasitic infection by increasing weight gain and wool production and reducing faecal egg output and parasite burden. In Fiji, field studies have shown that supplementation with urea-molasses blocks can result in increased live-weights of lambs at weaning, increased reproduction rates in maiden ewes and reduction in faecal egg output in grazing sheep. Additional benefits were derived from the inclusion of anthelmintic in the blocks in similar groups of sheep particularly during periods of greater susceptibility to parasites. Pen studies with young goats have shown that urea supplements alone gave no production benefits, but when accompanied by 100 g/d of cotton seed meal beneficial responses were observed. It is expected that parasite control in the small ruminant production systems of developing countries in south-east Asia and the Pacific Islands will benefit from the introduction of low cost nitrogen supplements along with anthelmintic therapy delivered strategically by molasses blocks.

Small volumes of oxygen introduced into vials of medium at pH 7 prepared under anaerobic conditions reacted with the medium during sterilization by heating, and also raised the redox potential. The partial pressure of oxygen (pO2) in the medium, and the redox potential (Eh) were measured and their effect on the number of spores of Clostridium botulinum type E required to produce growth, and hence on the probability of growth from single spore inocula, was determined. In the presence of a pO2 of up to 4·5 × 10−3 atm resulting in an Eh of c. + 217 mV, the probability of growth from single spores within 5 days at 20°C was equal to that in strictly anaerobic conditions at an Eh of − 400 mV. At pO2 values of between 5·3 × 10−3 atm and 8·4 × 10−3 atm corresponding to Eh values of between + 226 mV and + 254 mV an inoculum of between 10 and 1000 spores was required to produce growth and at pO2 values of between 1·12 × 10−2 atm,and 1·6 × 10−2 atm, corresponding to redox potentials of between + 271 mV and + 294 mV, the number of spores required to produce growth was between 2 × 104 and > 2 × 105. The relationship between pO2 and Eh depends on the chemical nature of a culture medium or food, and in order to assess the probable influence of these parameters on growth of C. botulinum in a medium or a food it is necessary to determine both the redox potential and the partial pressure of oxygen.