Anthelmintic resistance is a major problem in livestock, and while it has been slower to emerge in cattle, there are reports of its occurrence. Three broad-spectrum anthelmintics are available for use, and one mechanism of resistance that is common to all is target site alteration. Glutamate-gated chloride channels (GluCls) are an important target for macrocyclic lactone anthelmintics (MLs), while beta-tubulin represents the benzimidazole (BZ) target. The objectives of this thesis were to determine whether GluCls are involved in ML resistance in the cattle parasite Cooperia oncophora , and whether beta-tubulin is involved in BZ and ML resistance. Two isolates of C. oncophora were used. In a fecal egg-count reduction test, ivermectin was found to be 100% effective against one isolate (IVS), and only 77.8% effective against the second isolate (IVR). Two full-length GluCl cDNAs, encoding GluClalpha3 and beta subunits, were cloned. These subunits share high sequence identity with similar GluCl subunits from Haemonchus contortus and Caenorhabditis elegans. Genetic variability analysis of the two genes showed significant differences in allele frequencies between IVS and IVR worms at the GluClalpha3 gene, but not the GluClbeta gene, suggesting that the GluClalpha3 gene is involved in ivermectin resistance. Sequencing of full-length GluCl subunit cDNAs from IVS and IVR worms revealed the presence of mutations in the N-terminal domains. Mutations in the GluClalpha3 caused modest but significant reductions in glutamate, ivermectin and moxidectin sensitivity, while mutations in the GluClbeta abolished glutamate sensitivity. Of the three mutations identified in the IVR GluClalpha3, the L256F mutation accounted for the difference in glutamate and ivermectin response between IVS and IVR GluClalpha3 channels. Two beta-tubulin isotypes cloned from C. oncophora were found to share a high homology with beta-tubulin isotypes from other trichostrongylids. Gen

No description available.

O estudo dos teores protéicos oferecidos aos animais possui crucial importância, pois estes exercem influência determinante no desenvolvimento da infecção parasitária. Investigou-se o efeito da utilização de dois diferentes teores protéicos (18,5% e 8,6% de PB na MS) sobre as alterações fisiopatológicas desenvolvidas por bezerros primo infectados com o nematóide intestinal Cooperia punctata. Objetivando determinar se a suplementação possibilitaria aos animais infectados responderem mais prontamente ao desafio parasitário, realizaram-se estudos de composição corporal, retenção de compostos nitrogenados, acompanhamento clínico completo, avaliação de peso e carcaça, avaliação quantitativa e qualitativa da carga parasitária e exames histopatológicos. Os animais que receberam suplementação apresentaram um quadro clínico menos severo, perderam menos peso, tiveram um maior rendimento de carcaça, apresentaram lesões teciduais mais exuberantes, maiores taxas de excreção urinária de nitrogênio, expulsaram os parasitos para porções distais do trato gastrointestinal e demonstraram uma eficiência de retenção de nitrogênio 3,6 vezes maior que os animais mantidos na dieta basal. Demonstrou-se que a suplementação protéica resultou em efeitos positivos para os animais infectados. / The study of protein levels offered to cattle is very important when one aims at nematode control, since they can effectively affect the development of parasitic infection. The effect of two different levels - 18.5% and 8.6% CP on DM basis on the pathophysiology of Cooperia punctata infection on naive calves was examined. Aiming at determine if protein supplementation allow animals to better withstand parasitic challenge, several parameters were evaluated: body composition, nitrogen retention, clinical evolution, weight gain, carcass yeld, quantitative and qualitative assessment of parasitic burden and histopathology. Supplemented animal presented a milder clinical signs, lost less weight, had higher carcass yeld, greater tecidual lesions, higher urinary nitrogen excretion, expelled parasites to distal parts of gastrointestinal tract and showed a 3.6 greater efficiency for nitrogen retention than animal kept on basal diet. It became clear that protein supplementation resulted in benefits to infected animals.

O estudo dos teores protéicos oferecidos aos animais possui crucial importância, pois estes exercem influência determinante no desenvolvimento da infecção parasitária. Investigou-se o efeito da utilização de dois diferentes teores protéicos (18,5% e 8,6% de PB na MS) sobre as alterações fisiopatológicas desenvolvidas por bezerros primo infectados com o nematóide intestinal Cooperia punctata. Objetivando determinar se a suplementação possibilitaria aos animais infectados responderem mais prontamente ao desafio parasitário, realizaram-se estudos de composição corporal, retenção de compostos nitrogenados, acompanhamento clínico completo, avaliação de peso e carcaça, avaliação quantitativa e qualitativa da carga parasitária e exames histopatológicos. Os animais que receberam suplementação apresentaram um quadro clínico menos severo, perderam menos peso, tiveram um maior rendimento de carcaça, apresentaram lesões teciduais mais exuberantes, maiores taxas de excreção urinária de nitrogênio, expulsaram os parasitos para porções distais do trato gastrointestinal e demonstraram uma eficiência de retenção de nitrogênio 3,6 vezes maior que os animais mantidos na dieta basal. Demonstrou-se que a suplementação protéica resultou em efeitos positivos para os animais infectados. / The study of protein levels offered to cattle is very important when one aims at nematode control, since they can effectively affect the development of parasitic infection. The effect of two different levels - 18.5% and 8.6% CP on DM basis on the pathophysiology of Cooperia punctata infection on naive calves was examined. Aiming at determine if protein supplementation allow animals to better withstand parasitic challenge, several parameters were evaluated: body composition, nitrogen retention, clinical evolution, weight gain, carcass yeld, quantitative and qualitative assessment of parasitic burden and histopathology. Supplemented animal presented a milder clinical signs, lost less weight, had higher carcass yeld, greater tecidual lesions, higher urinary nitrogen excretion, expelled parasites to distal parts of gastrointestinal tract and showed a 3.6 greater efficiency for nitrogen retention than animal kept on basal diet. It became clear that protein supplementation resulted in benefits to infected animals.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.

The principle aim of the current research was to modify the larval development assay (LDA) for use with Cooperia from cattle. A series of experiments were conducted in order to modify the LDA protocol to determine the most appropriate culture media and incubation temperature. These initial experiments concluded that, of the protocols examined, a culture medium of 1/8th the concentration of E. coli (EC) + 1/4th the concentration of yeast extract (YE) as generally used to culture sheep nematodes, at a culture temperature of 18ºC, resulted in the optimum number of Cooperia larvae developed to the third larval stage (L3). However, the number of eggs that developed to L3 was still generally low. A comparison was then made using isolates from a farm with a history of resistance in Cooperia to ivermectin (IV) and benzimidazoles (BZ) and two farms with a history of no resistance in this parasite. These experiments were undertaken using 1/8EC + 1/4YE media protocol and 1/2EC + 1/2YE concentration of the standard culture media for sheep nematodes. These three isolates were cultured at temperature of 18ºC and 25 ºC in the commercially available DrenchRite® 96-well microtitre assay plates which contained BZ, levamisole (LV) and IV in doubling dilutions within an agar matrix. The LD50 values were determined from a dose response curve. The resulting LD50 values were very variable, especially for the IV analogues. There was no obvious difference between the resistant and susceptible farms for the LD50 values of BZ or IV. A secondary aim of this research was to investigate the potential usefulness of the larval feeding inhibition assay (LFIA). This was adopted as published and it was determined it could be used to distinguish between susceptible and resistant Teladorsagia circumcincta with a resistance ratio of at least six. This research concluded that further research is required to fully optimise the LDA for Cooperia in cattle but adequate dose response curves were determined to indicate it struggles to distinguish BZ and IV resistance. The LFIA deserves to be further investigated as it offers some scope to detect ivermectin resistance in cattle nematodes as the dose response curves demonstrated a good repeatability for T. circumcincta from sheep. Comparing LDA and LFIA, both assays seemed to be useful but the latter was considered to have greater potential.