Potential anthelmintic properties of nitrogenous fertilisers

Abstract

This dissertation describes a series of experiments designed to understand the potential anthelmintic properties of nitrogenous fertilisers for control of gastrointestinal parasites. Anthelmintic administration is no longer considered the sole method for control of gastrointestinal parasites. Due to the increasing levels of anthelmintic resistance, alternative methods of parasite control are required. Nitrogenous fertilisers produce a number of potentially toxic compounds during their conversion to plant available forms, and there are some reports they may have anthelmintic properties, although there is a paucity of specific evidence. Therefore, this series of experiments investigated the effects of nitrogen-containing fertilisers on Trichostrongylus colubriformis eggs hatching and larval development. Experiment one (Chapter 3) consisted of topical application of either water or urea (Flow-Fert N, 20% concentration) onto 100g of faeces. The total number of larvae collected per 100g of faeces was 25,600 and 800 for water and urea respectively, a 97% reduction in larvae following treatment with urea. Visual assessment of the faeces showed a white fungus growing on the faeces sprayed with water that was not present on the faeces sprayed with urea. The second experiment (Chapter 4) involved immersing T. colubriformis eggs in pH solutions ranging in whole number increments from 4 to 11, and in solutions of 20% urea (pH of 8). pH had a significant effect on egg hatching at pH less than 6 (P<0.001), whilst above pH 6 there was no effect on egg hatching. Urea solutions suppressed 90%+ of the eggs from hatching indicating that the effect on egg hatching was independent of pH. Experiment three (Chapter 5) determined the optimum concentration of urea required to inhibit eggs from hatching. T. colubriformis eggs were immersed in solutions of urea at various concentrations (1%, 2%, 4%, 6%, 8%, 10%, 20%, 50%). There was a significant effect of urea concentration on egg hatching with hatching decreasing as urea concentrations increased with less than 10% of eggs hatching in concentrations greater than 10%. Optimum concentrations estimated using an LD90 and ROC analysis were determined to be 19.6% and 5.5%, respectively. The fourth experiment (Chapter 6) compared five nitrogen-containing fertilisers: urea (46-0-0-0), sulphate of ammonia (21-0-0-24), potato fertiliser (15-10-10-8), potassium nitrate (13-0-44-0) and nitrophoska blue (12-5.2-14-0) at various concentrations (1%, 5%, 10%, 20% and 50%) and their effects on eggs hatching. There was a fertiliser type X concentration interaction with all fertilisers, at concentrations greater than 10% inhibiting eggs from hatching to less than 6% (P<0.001). At a concentration of 1%, sulphate of ammonia and potassium nitrate had the strongest effect on eggs hatched, viz 24% and 48%, respectively, in comparison with 90% in the control. Regression analysis credited the variation in percentage of eggs hatched could be explained by both nitrogen percentage and electrical conductivity, but not phosphorous, potassium, sulphur levels or pH. The final experiment (Chapter 7) considered the implications of four of the fertilisers and whether exposure to the fertilisers was reversible. Following 24hours of immersion in the solution, and a further 24hours of incubation in water, no eggs had hatched under any of the fertilisers (20% concentration), indicating a strong, irreversible effect on the eggs (P<0.001). Nitrogenous fertilisers have the potential to control ruminant GINs outside of the host, as an alternative to anthelmintics. These fertilisers break the lifecycles of the parasites, however more research is required regarding the components of the fertilisers that are toxic to the nematodes and whether these in vitro studies can be transferred into the field and remain successful.