SUMMARY Previous experiments have shown that genetic resistance to infection by Teladorsagia circumcincta in sheep can be measured by the level of IgA in gastric mucus, jointly with other parameters. The aim of this study has been to observe the influence of IgA on adult worms. The experiment was carried out with Churra sheep experimentally infected with T. circumcincta. At slaughter, gastric content, gastric mucus, blood samples and faeces were recovered to determine the number of eggs in utero, length of adult females, worm burden, number of L4, titre of serum pepsinogen, peripheral eosinophilia and eggs per gram (epg). IgA activity in gastric mucus, serum, nasal secretions and saliva were tested against somatic antigen from fourth-stage larvae (L4), somatic antigen from the adult stage and excretory-secretory (E/S) antigen from the adult stage. The results showed a significant correlation between serum IgA and gastric mucus (P<0.01) as well as in nasal secretions (P<0.01). We found negative correlations between IgA activity in gastric mucus with the eggs in utero and with adult female length. Furthermore there were also strong relationships between the peripheral eosinophilia with serum (P<0.01) and gastric mucus IgA activity (P<0.01). Moreover serum pepsinogen and the number of L4 at slaughter were related (P<0.01).

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A survey to determine the prevalence of anthelmintic resistance in nematode parasites of sheep against the three main families of anthelmintics (benzimidazoles, macrocyclic lactones and imidazothiazoles) was carried out from January 1999 to December 2003 involving 85 flocks in Northwest (NW) Spain. In the study on prevalence of resistance to benzimidazoles, faecal egg count reduction test (FECRT) showed there was resistance in 8 (12.7%) flocks, 1 (1.6%) was suspected, and 54 (85.7%) were susceptible. The results indicated that 9 flocks (34.61%) showed resistance, 1 (3.85%) showed suspected resistance, and 16 (61.54%) were susceptible to the imidazothiazoles. Against macrocyclic lactones, resistance was observed in 8 flocks (15.69%), 4 (7.84%) showed suspected resistance and 39 (76.47%) were susceptible. None of the flocks used in the study showed resistance to the three families of anthelmintics. Nevertheless, six were recorded as resistant or suspected of being resistant to two of these families of anthelmintics. Egg hatch assay (EHA) and FECRT were carried out jointly on 61 flocks, although EHA was done on a total of 83 farms. The results showed that 15 (18.07%) of the 83 flocks were resistant, with egg death 50 over 0.1 microg/ml thiabendazole, and 68 (81.93%) were susceptible to benzimidazoles. When the results between FECRT and EHA were compared, both techniques showed good correlation in field studies. Faecal cultures performed pre- and post-treatment indicated that Teladorsagia and Trichostrongylus were the main genera.

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SUMMARY The aim of this study was to understand the influence of a low protein diet on the resistance of the Churra breed sheep to infection with Teladorsagia circumcincta. A previous experiment in our department demonstrated significant differences between resistant and susceptible sheep infected with T. circumcincta, in eggs per gram of faeces, serum pepsinogen, serum IgA and peripheral eosinophilia (unpublished). The sheep were fed with a balanced protein diet. In the current assay there were significant differences between the resistant and susceptible groups in egg output, serum pepsinogen and worm burden. The optical densities (OD) of the IgA in blood samples, nasal secretions and saliva were tested throughout the study and the differences between groups were not significant. At necropsy adult worm length, the number of eggs in utero in adult females, the number of fourth stage larvae and the OD of gastric mucus IgA did not differ between groups either. Moreover, due to diet there was a loss of weight in both groups but this was not significant. Our results support the view that low protein diets could influence immune function and as a result resistant genotypes do not show any superiority in comparison with susceptible ones.

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