Studies on the pathophysiology and immune response to Ostertagia ostertagi in cattle

The studies reported in this thesis were undertaken to examine in detail several aspects of infection with Ostertagia ostertagi in cattle. The effect of age on the development of immunity was investigated and an attempt was made to immunise calves against O. ostertagi. More detailed work was concerned with the interaction of the parasite at the mucosal surface of the abomasum, together with the pathophysiological changes in the parasitised host. Section I describes two experiments on the immune response of cattle to Ostertagia. The first was designed to ascertain whether immunity to ostertagiasis developed more quickly in 9-15 month old cattle than in calves. Although there was evidence of two manifestations of resistance, namely reduced worm size and fecundity, the study demonstrated that worm establishment was not markedly affected by the age of the host and suggested that natural age resistance is not significantly developed in 9-15 month old cattle. In the second experiment, an attempt was made to immunise calves against O. ostertagi using a closely related parasite Ostertagia leptospicularis which has been shown to induce a marked reaction in the abomasum of calves. Two doses of either O. ostertagi. O. leptospicularis or a combination of O. ostertagi and O. leptospicularis were given to young calves prior to challenge with O. ostertagi but none of these immunising regimens conferred protection and similar challenge burdens were recovered from all of the calves at post mortem examination. The major part of this thesis was concerned with studies on the biochemical and hormonal changes which occur in the host as a result of infection with larval and adult O. ostertagi and these are described in Section 2. In Experiment 3, calves were infected with 50,000 O. ostertagi L3 and serum pepsinogen and gastrin levels measured; these rose markedly from day 15 after infection and peaked between days 20 and 30. Experiments 4, 5 and 6 were designed to investigate the role of the adult parasite in the pathophysiological changes in the host. Serum pepsinogen levels rose consistently when animals were exposed to adult parasites. However, serum gastrin levels only rose in response to large numbers of adult worms and the association of these changes with altered abomasal pH are discussed. Lesions were observed in the abomasa of calves which were infected with adult parasites only and a further experiment (Experiment 7) was carried out to determine whether the intimate association of the parasites with the mucosal surface was responsible for the pathological and physiological changes which took place. During this study, it was apparent that adult Ostertagia were quickly killed when restricted and suspended in chambers in the abomasum and it was then concluded that the parasites require the microenvironment close to the epithelium for their survival. No pathophysiological changes were observed probably due to the early mortality of the adult parasites in this experiment. The two remaining experiments in Section 2 were designed to investigate changes in pepsinogen and gastrin levels which occur in naturally acquired Ostertagia infections in the field. Animals in Experiment 8 were kept for two seasons under typical husbandry conditions and plasma pepsinogen and gastrin levels were recorded regularly. Values for pepsinogen and gastrin rose to two peaks as Type I and Type II ostertagiasis developed and subsequently fell as the animals recovered. The pepsinogen levels did not return to pre-infection values either during the pre-Type II period, or during the second grazing season when immunity had developed. The aetiology of the raised pepsinogen values observed during the second grazing season were further investigated in Experiment 9. Immune adult dairy cows which had been housed for the winter period were challenged with Ostertagia larvae and blood was collected routinely for the estimation of serum pepsinogen and gastrin. Pepsinogen levels rose to about 3.0 i.U. Tyrosine within 3 days of challenge while gastrin levels remained at pre-infection levels. It was concluded that Ostertagia larvae may induce a hypersensitive response in the abomasa of immune cattle with a consequent leakage of pepsinogen into the blood

Animal Health and the Role of Pharmaceuticals

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Pharmacologie des antiinflammatoires non steroidiens chez les bovins

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Intramammary treatment of mastitis in cows

Copyright 2007 Elsevier B.V., All rights reserved.Peer reviewe

Therapie Anthelminthique Bovins les systemes remanents

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The health of the sheep industry and the medicines to maintain it

The global sheep industry is changing dramatically to serve its diverse customers and in response to liberalised international trade agreements and resculptured (reduced) national subsidies. A drive for efficiency gains together with greater awareness of animal related public health issues means that there is a focus on disease reduction and welfare issues in sheep husbandry. Particular advances have been made in the rational use of anthelmintics, antibiotics and anti-inflammatory analgesics in sheep and veterinarians and drug licensing authorities must utilise these advances to the benefit of the health of the sheep industry.Peer reviewe

Drug dosages for small mammals

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Antimicrobial resistance: a veterinary perspective

Bacterial disease is a major constraint on the efficient production of animal derived food and causes ill health and suffering in both food producing and companion animals. In some production systems the spread of bacterial disease may be accelerated by the proximity of the animals. Bacterial disease may be controlled in some situations by eradication, maintenance of animals of specified health status, vaccination, and good hygiene. Nevertheless, antimicrobial chemotherapy remains vitally important for treating and in some cases preventing bacterial disease. Many bacterial diseases of animals are potentially fatal; others cause pain and distress. Appropriate use of antimicrobials will cure some sick animals and speed the recovery of others, and may improve the welfare of treated animals and reduce the spread of infection to other animals or, in the case of zoonotic disease, to humans. The challenge is to use antimicrobials wisely, minimising the risk of resistancePeer reviewe

Ecotoxicology and residues of anthelmintic compounds

Anthelmintics and endectocides used for the treatment and prophylaxis of Ostertagia sp. in ruminants include benzimidazoles, levamisole, morantel and the avermectins and milbemycins. Most of these agents are excreted to some extent in the faeces of treated animals and it has been demonstrated that members of the avermectin/milbemycin group may have deleterious effects on non-target organisms utilising the faeces. The environmental impact of antiparasitic chemotherapy depends on the deleterious effect which the agent or its metabolites have on organisms in the locus of the excreta. the amount of active agent excreted, the temporal nature of the excretion and the stability of the ecotoxic residues. These have to be considered in the context of the overall proportion of excreted faeces from a herd which is contaminated and thus the availability of non-contaminated faeces which may act as refugia for dung utilising organisms. The contribution which weathering, faunal inhabitants, trampling by cattle and disturbance by birds have on the rate of dung degradation must also be considered. The greatest ecotoxicological risk is associated with sustained release delivery devices, delivering endectocides with potent activity against dipteran flies and coleopteran beetles. The relatively large proportion of most cattle herds excreting faeces with no endectocidal contamination is likely to reduce the impact that such treatment or prophylactic strategies have on non-target organisms. (C) 1997 Elsevier Science B.V.Peer reviewe

Pharmacokinetics and clinical effects in dogs of a sustained-release formulation of theophylline

Theophylline was administered orally in a sustained-release preparation at a dose rate of 20 mg/kg bodyweight to six beagle dogs. A mean (+/- se) maximum plasma concentration of 12.2 +/- 0.65 micrograms/ml was obtained 5.17 +/- 0.70 hours after administration and it was calculated to have a mean residence time of 9.09 hours. When given at 40 mg/kg bodyweight twice daily for five days the theophylline preparation was well tolerated, but, the dogs developed a marked tachycardia and hyperpnoea which were attributed to the high plasma concentrations (> 30 micrograms/ml) reached during this dosage regimen.Peer reviewe