Effect of level of infection by gastrointestinal nematodes and anthelmintic treatment on milk yield in dairy sheep.

The effects of gastrointestinal nematode infections and anthelmintic treatment on milk yields was compared between flocks with a low level (LL) of eggs per gram (epg) before partum and with a high level (HL). Faecal egg count reduction tests (FECRTs) were carried out before partum comparing a treated group with netobimin with an untreated group. Ewes belonging to LL flocks produced 55.4% more milk than ewes from HL flocks. A negative correlation was found between the mean epg before treatment and the mean milk yield per flock (r = -0.860; p < 0.01). However, treated ewes produced 10.1% more milk than untreated ewes in LL flocks, although in HL flocks, treated ewes produced less milk (-2.7%). The treatment of flocks even with low levels of infection can improve the milk yields. In this study, the epg before partum had a greater influence on total milk yield than the anthelmintic treatment.

TITLE: Effet du niveau d'infection par les nématodes gastro-intestinaux et du traitement anthelminthique sur le rendement laitier des brebis laitières. ABSTRACT: Les effets sur les rendements laitiers des infections à nématodes gastro-intestinaux et d'un traitement anthelminthique ont été comparés entre des troupeaux avec un bas niveau (BN) d'œufs par gramme (opg) avant la mise bas et d'autres avec un haut niveau (HN). Un test de réduction du nombre d'œufs dans les selles (FECRT) a été effectué avant la mise bas en comparant un groupe traité avec de la nétobimine avec un groupe non traité. Les brebis appartenant aux troupeaux BN ont produit 55,4 % de lait de plus que les brebis des troupeaux HN. Une corrélation négative a été trouvée entre l'opg moyen avant traitement et le rendement laitier moyen par troupeau (r = −0,860 ; p < 0,01). Cependant, les brebis traitées ont produit 10,1 % de lait de plus que les brebis non traitées dans les troupeaux BN, bien que dans les troupeaux HN les brebis traitées aient produit moins de lait (−2,7 %). Le traitement des troupeaux, même ceux avec de faibles niveaux d'infection, peut améliorer les rendements laitiers. Dans cette étude, l'opg avant mise bas a eu une plus grande influence sur la production totale de lait que le traitement anthelminthique.

Loop-mediated isothermal amplification (LAMP) assay for the diagnosis of fasciolosis in sheep and its application under field conditions.

BACKGROUND: Loop-mediated isothermal amplification (LAMP) is a very specific, efficient, and rapid gene amplification procedure in which the reaction can run at a constant temperature. In the current study we have developed a LAMP assay to improve the diagnosis of Fasciola spp. in the faeces of sheep. FINDINGS: After the optimisation of the LAMP assay we have shown similar results between this technique and the standard PCR using the outer primers of the LAMP reaction. In both cases the limit of detection was 10 pg; also, the diagnosis of fasciolosis was confirmed during the first week post-infection in experimental infected sheep by both techniques. In eight naturally infected sheep, the infection with F. hepatica was confirmed in all animals before a treatment with triclabendazole and on day 30 post treatment in two sheep using the LAMP assay; however, when we carried out the standard PCR with the outer primers, the results before treatment were the same but on day 30 post-treatment the infection was only confirmed in one out of the two sheep. On the other hand, the standard PCR took around 3 h to obtain a result, comparing with 1 h and 10 min for the LAMP assay. CONCLUSIONS: The LAMP assay described here could be a good alternative to conventional diagnostic methods to detect F. hepatica in faeces since it solves the drawbacks of the standard PCR.

Screening anthelmintic resistance to triclabendazole in Fasciola hepatica isolated from sheep by means of an egg hatch assay.

BACKGROUND: In the present study, the detection of anthelmintic resistance to triclabendazole (TCBZ) in sheep infected by Fasciola hepatica was studied using an egg hatch assay (EHA). F. hepatica eggs were recovered from bile and faeces of infected animals by isolates with different grade of anthelmintic resistance to TCBZ: i) a resistant isolate (RT); ii) a susceptible isolate (ST); iii) naturally infected sheep by a susceptible field strain (FST). In the EHA the percentage of hatched eggs were calculated according to the following concentrations of TCBZ diluted in dimethyl-sulfoxide (DMSO): 0.05, 0.2, 1, 5, and 25 µg/ml. RESULTS: In relation to the EHAs carried out with the eggs from bile of sheep infected by ST, differences were found in the percentage of hatched eggs between the control well, only with DMSO, and the two highest concentrations of TCBZ (5 and 25 µg/m) (p < 0.05). However, when we tested the drug with the eggs from the bile of sheep infected by RT, the percentage of hatched eggs was similar among all concentrations. Since the range of hatching varied between isolates, we calculated the ratio of the results of each concentration to its control value confirming the higher hatching in RT than in ST. We developed an EHA with eggs recovered from faeces in order to avoid the slaughter of sheep. The results of the EHAs with the isolate ST showed differences in the percentage of hatching between the highest concentration (25 µg/ml) and the control well (p < 0.05); however, these differences were not confirmed under field conditions with the strain FST. CONCLUSIONS: The ovicidal effect of TCBZ in F. hepatica eggs from bile was shown using a commercial formulation diluted in DMSO with a minimum concentration of 5 µg/ml. However, in eggs recovered from faeces the results are not conclusive. The cleaning of eggs recovered from faeces is an important issue that should be reviewed and standardized before comparing results between susceptible and resistant isolates in this kind of EHA.

Pyrosequencing analysis of the beta-tubulin gene in Spanish Teladorsagia circumcincta field isolates.

Benzimidazole (BZ) resistance in gastrointestinal nematodes has been associated with single nucleotide polymorphisms (SNPs) at codons 200, 167 and 198 in the beta-tubulin isotype 1 gene and, recently, these SNPs have also been found in macrocyclic lactone (ML) resistant strains of Haemonchus contortus. On this basis, we have studied the same putative SNPs in Spanish Teladorsagia circumcincta field isolates by pyrosequencing. Single L3 (infective 3rd stage larvae) from five sheep flocks were tested after confirming their BZ susceptibility and degree of ivermectin (IVM) resistance. According to the Faecal Egg Count Reduction Test (FECRT) one flock was classified as IVM susceptible, another one was resistant, and the rest had a suspicion of resistance to IVM. DNA extraction was carried out on 598 single L3 and 56% of these were identified as T. circumcincta after the amplification of a species-specific ITS2 fragment. The number of L3 analyzed for the SNPs 198/200 was 255 and for the SNP 167 was 187. Results clearly indicate no resistance-associated SNPs were present at any codon, before or after treatment. Therefore, all T. cicumcincta L3 were designated as susceptible homozygous genotypes for all SNPs. The absence of the mutations in these populations would argue against resistance haplotypes being present in the parasite population prior to drug treatment, at least in Spanish T. circumcincta.

Efficacy of nitroxynil against Fasciola hepatica resistant to triclabendazole in a naturally infected sheep flock.

The aim of this study was to compare the efficacy of triclabendazole (TCBZ) and nitroxynil against a TCBZ-resistant Fasciola hepatica strain in a naturally infected sheep flock. The efficacies were measured by the faecal egg count reduction test. The level of F. hepatica antigens was tested in faeces; and haematological indices such as total proteins (TP), albumin, hepatic enzymes and total IgG were also studied. The results confirmed the resistance of F. hepatica against TCBZ in the flock with an efficacy during the first month post-treatment between 59.4% and 73.8%. In the nitroxynil group, the efficacy during the same period ranged between 81.3% and 86%, likely because the efficacy of this drug against 7- to 9-week-old immature stages is only 50-90%. Anemia was showed in all groups and white blood cells were always higher than the reference range. The values of TP and albumin were within normal range in most of the sheep, and an increase in hepatic enzymes confirmed the liver damage. Regarding total IgG, some negative correlations were found with egg excretion, and in relation to the level of antigens in faeces, these ones decreased immediately after treatment. We conclude that nitroxynil could be an alternative in case of TCBZ resistance.

Quantitative trait loci for resistance to trichostrongylid infection in Spanish Churra sheep.

BACKGROUND: For ruminants reared on grazing systems, gastrointestinal nematode (GIN) parasite infections represent the class of diseases with the greatest impact on animal health and productivity. Among the many possible strategies for controlling GIN infection, the enhancement of host resistance through the selection of resistant animals has been suggested by many authors. Because of the difficulty of routinely collecting phenotypic indicators of parasite resistance, information derived from molecular markers may be used to improve the efficiency of classical genetic breeding. METHODS: A total of 181 microsatellite markers evenly distributed along the 26 sheep autosomes were used in a genome scan analysis performed in a commercial population of Spanish Churra sheep to detect chromosomal regions associated with parasite resistance. Following a daughter design, we analysed 322 ewes distributed in eight half-sib families. The phenotypes studied included two faecal egg counts (LFEC0 and LFEC1), anti-Teladorsagia circumcincta LIV IgA levels (IgA) and serum pepsinogen levels (Peps). RESULTS: The regression analysis revealed one QTL at the 5% genome-wise significance level on chromosome 6 for LFEC1 within the marker interval BM4621-CSN3. This QTL was found to be segregating in three out of the eight families analysed. Four other QTL were identified at the 5% chromosome-wise level on chromosomes 1, 10 and 14. Three of these QTL influenced faecal egg count, and the other one had an effect on IgA levels. CONCLUSION: This study has successfully identified segregating QTL for parasite resistance traits in a commercial population. For some of the QTL detected, we have identified interesting coincidences with QTL previously reported in sheep, although most of those studies have been focused on young animals. Some of these coincidences might indicate that some common underlying loci affect parasite resistance traits in different sheep breeds. The identification of new QTL may suggest the existence of complex host-parasite relationships that have unique features depending on the host-parasite combination, perhaps due to the different mechanisms underlying resistance in adult sheep (hypersensitivity reactions) and lambs (immunity). The most significant QTL identified on chromosome 6 for LFEC(1) may be the target for future fine-mapping research efforts.