Epsilon Archive for Student Projects

Abstract

Nematodirus spp., along with other gastrointestinal nematodes, are a common cause of
disease among sheep and remains a major animal health concern, and cause of reduced
productivity for sheep farmers around the world. As the resistance against anthelmintics is
substantial among gastrointestinal nematodes, there is an urgent need of significant
alternatives to anthelmintic treatment. The life cycle of Nematodirus comprises stages both
within and outside the host, with the pre-parasitic development to the infective third stage,
occurring on pasture. With evidence suggesting that nitrogenous fertilisers could have the
ability to inhibit egg hatching and larval survival in numerous gastrointestinal nematodes, the
aim of this study was to investigate urea’s ability, in situ, to break the life cycle of
Nematodirus spp. outside of the host. The method used was through targeted application of
liquid urea to experimental pastures at times when Nematodirus eggs are present on pasture.
The study included seven experimental paddocks previously grazed by sheep with a known
infestation of Nematodirus spp. and other Strongyles. The sheep were of different genetic
lines, bred for either resistance or resilience against gastrointestinal nematodes. The
application of liquid urea involved five repeated sprayings of 40kg N/ha every three weeks
before the start of grazing season, or one single spraying of 200kg N/ha three months before
start of grazing, with control paddocks left untreated. The effect of treatments was evaluated
utilising three methods, i.e. observing pasture larval concentration, faecal egg counts and
concentration of eggs and larvae in soil. The study had a main focus on Nematodirus spp.,
although “other” Strongyles were included in the results to give a better understanding of the
overall effects of the treatments. Overall the results were equivocal, with absence of
consistently statistically significant differences between treatments and control. However not
significant, although a subject for discussion, was that urea could have a stimulating effect on
egg hatching and larval development. In conclusion, the results from this field trial have
demonstrated insufficient evidence that nitrogenous fertilisers provide epidemiological
benefits in reducing larval contamination on pasture. It has been demonstrated that it is
challenging to translate the in vitro results into the field, with the parasite having complex
hatching requirements arising of the environment, thus difficult to influence.