Inheritance of faecal nematode egg count in Barbari goats following natural Haemonchus contortus infection

Genetic parameters for faecal nematode egg count were estimated in naturally infected Barbari goats maintained at the Central Institute for Research on Goats, Makhdoom, Mathura, India, over a period of 5 years (1999 through 2003). Faecal egg count (FEC) data on 891 records of Barbari goats descended from 69 bucks and 241 does were used in this study. Analyses were carried out by restricted maximum likelihood (REML), fitting an animal model and ignoring or including maternal genetic or permanent environmental effects. Three different animal models were fitted. Direct heritability estimates were inflated substantially for this trait when maternal effects were ignored. The direct heritability estimates for the trait ranged from 0.05 to 0.13 depending on the model used. Low (0.04) maternal heritability estimate was observed for this trait in our study. Moderate estimate of the fraction of variance due to maternal permanent environmental effects (c(2)) for faecal egg count (c(2)=0.10) was also observed. Results suggest that direct and permanent environmental maternal effects were important for this trait, however, maternal additive effects had less impact on this trait.     

The relation between the natural worm burden of steers and the faecal egg count differentiated to species

The relation between the faecal egg count and the worm burden was investigated in 104 steers of three breeds, 9–24 months of age, which were subjected to natural infection with nematode larvae from pasture at The National Cattle Breeding Station near Rockhampton in central Queensland. The worm species found were Cooperia spp., Haemonchus placei, Trichostrongylus axei, Oesophagostomum radiatum and small numbers of Bunostumum phlebotumum.

The faecal egg count was found to be a reliable measure of the size of the worm burden. Steers slaughtered at 24 months of age had 90% fewer worms and 96% fewer eggs g⁻¹ faeces (P < 0.001) than those slaughtered at 9 months of age. Adjusted for age, the estimated faecal egg count increased 14 times (95% confidence limits 7.2, 35) for each 10-fold increase in estimated worm numbers.

The proportion of each species of larvae obtained from faecal culture (larval differential count) was related to the composition of the worm burden as measured by the proportion of worms in selected maturity categories and in selected length categories for each species (P < 0.001).     

A survey of seasonal changes in nematode faecal egg count levels of sheep and goats in Senegal

A survey of the gastro-intestinal nematodes in domestic sheep and goats of the Sahelian zone of Senegal was undertaken. Their prevalence and the egg production were estimated by faecal egg count in 2234 sheep and 577 goats slaughtered at the Dakar slaughterhouse during a 12 month period. The highest prevalence (%) and highest mean egg counts (EPG) were recorded at the end of the wet season. Amongst the species of nematodes encountered there are two of potential importance: Haemonchus contortus and Oesophagostomum columbianum. It is suggested that the most effective control can be achieved by a critical treatment at the end of dry season (May–June) when the EPG starts to increase, and when hypobiosis is supposed to be terminating. This would insure the greatest proportion of the existing worm population to be exposed to the anthelmintic.     

Intron 1 of the interferon gamma gene: Its role in nematode resistance in Suffolk and Texel sheep breeds

Genetic variation at intron 1 of the interferon gamma gene has recently been associated with variation in faecal egg count in Romney, Merino and Soay breeds of sheep. The Texel breed is more resistant to gastrointestinal nematode infection than the Suffolk breed, based on faecal egg count. Hence, the objective of this experiment was to characterise the polymorphisms of intron 1 of the interferon gammagene in Suffolk and Texel sheep, and to determine if the characterised haplotype variants were associated with faecal egg count variation in these breeds. Intron 1 haplotypes and faecal egg measurements were determined for Suffolks (n=113) and Texels (n=135). Four haplotypes were identified in Suffolks (A, B, C and D), two haplotypes as previously described, and two previously unknown haplotypes. However, there was no association between interferon gamma intron 1 haplotype and faecal egg count in Suffolks. In contrast, two previously identified haplotypes (A and B) were present in the Texel breed, and the B haplotype was associated with resistance to nematode infection (P=0.02). These results suggest that intron 1 of the interferon gamma gene has an important role in resistance to nematode infection in the Texel breed.     

Interpretation of serum antibody response to Anoplocephala perfoliata in relation to parasite burden and faecal egg count

REASON FOR PERFORMING STUDY: Increased knowledge is needed to assist in the interpretation of presently available diagnostic techniques for infection by the tapeworm Anoplocephala perfoliata in horses. HYPOTHESIS: The suggested cut-off level of an A. perfoliata specific ELISA may not adequately reflect the actual infection level. Hence, faecal egg counts may be a more useful diagnostic test for individual horses than previously reported. METHODS: Eighty-four horses admitted for slaughter at a Danish abattoir were examined for the presence of A. perfoliata. The number of tapeworms, their stage of development and gross pathological mucosal lesions were recorded and compared with serum antibody responses and faecal egg counts. Faecal egg counts were determined in samples from A. perfoliata infected horses using a semi quantitative centrifugation/flotation technique. Blood samples collected at slaughter were analysed by ELISA to determine serum antibody levels against A. perfoliata 12/13 kDa excretory/secretory antigens. RESULTS: Macroscopically visible tapeworms were detected in 24 (29%) of the horses. The overall sensitivity of the faecal egg count was found to be 0.46; however, if the detection limit was increased to above 20 tapeworms, sensitivity increased to 0.89. There was a correlation of 0.71 between worm burden and egg count. The antibody levels correlated significantly with infection intensity despite a wide variation among horses with similar levels of infection. The optimal cut-off value was determined using receiver operating characteristic analysis. If cut-off was chosen at optical density (OD) = 0.7, sensitivity was 0.68 and specificity 0.71. CONCLUSIONS: Both diagnostic methods were capable of revealing potentially pathogenic infections, with the faecal egg count being more applicable on the individual horse level. POTENTIAL RELEVANCE: In the population of Danish horses investigated the serum ELISA test should be interpreted such that horses in need of anti-Anoplocephala treatment have an OD = 0.7 or above.     

Relationships among peripheral eosinophilia, eosinophil peroxidase activity, interleukin-5 concentration and faecal nematode egg count during natural, mixed gastrointestinal nematode infection

A longitudinal study of sheep, naturally infected with gastrointestinal helminths, was carried out to quantify the relationships among eosinophilia, eosinophil peroxidase activity, interleukin-5 level and faecal egg counts. Faecal egg counts, peripheral eosinophilia and peroxidase activity per eosinophil were moderately repeatable but interleukin-5 concentrations had a remarkably high repeatability. Animals with higher concentrations of interleukin-5 had greater peripheral eosinophilia and those animals with higher numbers of eosinophils had lower faecal egg counts. These associations were statistically significant but quite weak. Variation in interleukin-5 levels does not appear to be responsible for most of the variation in eosinophil responses in outbred sheep.     

Effect of strategic gastrointestinal nematode control on faecal egg count in traditional West African cattle

This paper reports on the effect of strategic anthelmintic treatments and other determinants on faecal egg counts (FEC) of Trichostrongyles in N'Dama cattle of a west African village. Initially, 527 animals from 13 private N'Dama cattle herds were monitored in a longitudinal study from October 1989 to December 1994. Each herd was stratified by age and animals were sequentially allocated to two groups with similar age distributions. One group received a single anthelmintic treatment of fenbendazole (7.5 mg/kg BW), in October 1989 (n = 250), whereas the other group remained untreated (n = 277) throughout the study. In the next rainy season (June to October), the treated animals were treated twice (in July and September). The same treatment schedule was used in the subsequent rainy seasons until December 1994. Biannual anthelmintic treatments decreased the level of FEC between 31% (late dry season) and 57% (rainy season), when compared to untreated controls. The highest levels of FEC were found during the rainy season from June to October. FEC levels decreased until 4 years of age, after which they remained on a constant low level. The variability of returns to anthelmintic treatments between herds did not seem to be influenced by FEC at the herd level. The financial evaluation of anthelmintic interventions cannot be predicted from FEC and must necessarily rely on the direct monitoring of livestock productivity parameters.     

Intron 1 of the interferon γ gene: Its role in nematode resistance in Suffolk and Texel sheep breeds

Genetic variation at intron 1 of the interferon gamma gene has recently been associated with variation in faecal egg count in Romney, Merino and Soay breeds of sheep. The Texel breed is more resistant to gastrointestinal nematode infection than the Suffolk breed, based on faecal egg count. Hence, the objective of this experiment was to characterise the polymorphisms of intron 1 of the interferon gammagene in Suffolk and Texel sheep, and to determine if the characterised haplotype variants were associated with faecal egg count variation in these breeds. Intron 1 haplotypes and faecal egg measurements were determined for Suffolks (n=113) and Texels (n=135). Four haplotypes were identified in Suffolks (A, B, C and D), two haplotypes as previously described, and two previously unknown haplotypes. However, there was no association between interferon gamma intron 1 haplotype and faecal egg count in Suffolks. In contrast, two previously identified haplotypes (A and B) were present in the Texel breed, and the B haplotype was associated with resistance to nematode infection (P=0.02). These results suggest that intron 1 of the interferon gamma gene has an important role in resistance to nematode infection in the Texel breed.     

Association between variation in faecal egg count for a mixed field-challenge of nematode parasites and ovine MHC-DQA2 polymorphism

The selection of sheep that are resistant to gastrointestinal parasites and have lower faecal egg counts (FECs) has been the subject of extensive research. This has led to the speculation that the Major Histocompatibility Complex (MHC) genes could be used as markers to reduce FEC. In this study, associations between variation in ovine MHC-DQA2 and various measures of FEC recorded at two times (approximately 4 and 9 months of age) were investigated in a large group of New Zealand lambs (n=4676), derived from 185 different sire-lines, of a variety of breeds and raised on 25 separate farms. Pair-sample t-tests revealed that FEC for Nematodirus spp., Strongyle spp. and total FEC differed significantly between the two assessments. A total of twenty one DQA2 alleles or DQA2-DQA2-like haplotypes were identified, with allele/haplotype presence and frequency varying significantly between farms. For example, allele *0103 was observed on all farms, ranging in frequency from 0.2 to 60.9%, while haplotype *0101-*1601 was only present on one farm, in two lambs. A number of associations between the presence/absence of these alleles and egg counts were observed, but nearly all the allelic/haplotypic associations were age and parasite specific, suggesting that immune response is both age and challenge (parasite species mix) dependent. The exception was allele *1201 which was associated with increased total FECs at both 4 and 9 months of age; with it either being, or tending toward being, significantly associated with both increased Strongyle spp. and Nematodirus spp. counts as well. However, the observed increases in egg counts were small and ranged between 5 and 32 eggs per gram. In conclusion, we believe that the MHC plays an important role in parasite resistance, but that the MHC-nematode interaction is complex and thus the development of a single gene-marker based on the "MHC effect" is unlikely.     

Sensitivity of the breeding values for growth rate and worm egg count to environmental worm burden in Australian Merino sheep

The objective of this study was to explore the sensitivity of breeding values for growth rate and worm egg count (WEC, cube root transformed) to environmental worm burden, measured as the average WEC for each contemporary group (CGWEC). Growth rate and WEC were measured on 7,818 naturally infected Merino lambs in eight flocks across Australia, linked through common use of AI sires. Through bivariate analysis, genetic correlations of 0.55 ± 0.23 and 0.30 ± 0.16 were found for growth rate and WEC between low and high CGWEC, respectively. In a second analysis, breeding values for growth rate and WEC were regressed on CGWEC with a random regression model. The heritability for growth rate varied from 0.23 to 0.16 from low to high CGWEC, and the heritability for WEC varied from 0.25 to 0.36. Results suggest that breeding values for both growth rate and WEC are sensitive to environmental worm burden. Animals expressed less genetic variation for growth rate and more genetic variation for WEC in high CGWEC than in low CGWEC. This form of genotype‐by‐environment interaction should therefore be considered in genetic evaluation of both growth rate and WEC, to increase the efficiency of selection for animals that are more parasite resistant and more resilient to environmental worm challenge.     

A small scale survey of ivermectin resistance in sheep nematodes using the faecal egg count reduction test on samples collected from Scottish sheep

Thirty-eight sheep flocks, predominantly from the south/central Scotland, were examined using a faecal egg count reduction test (FECRT) for the presence of ivermectin (IVM) resistant nematodes. Efficacies of less than 95%, 14-17 days post-treatment, were identified in 6 of 17 naturally grazing flocks where pre-treatment faecal egg counts were in excess of 150 eggs per gram. Efficacies on these IVM resistant farms ranged from 66 to 92%. One other suspected cases of IVM resistance was also identified in returned material. The larvae detected in post-treatment coprocultures from resistant flocks were from the genera Teladorsagia (4 from 6) and Trichostrongylus (2 from 6).     

Effects of challenge with trichostrongylid nematode larvae on immunologically resistant grazing yearling sheep in South Australia.

Paddocks near Gawler, South Australia, were grazed by newly weaned sheep which received either no anthelmintic treatment, regular 3-weekly treatment or a single treatment in February. A decline in the faecal egg count of untreated sheep in autumn associated with the ingestion of infective larvae indicated that the sheep had developed a resistance to reinfection. At the end of the experiment, 10 sheep were experimentally infected with Trichostrongylus vitrinus larvae to demonstrate this resistance. Untreated sheep grew less wool and had lower body weights when compared with treated animals and were extremely 'daggy'. A single treatment in February did not prevent production losses or scouring.     

Repeated treatment faecal egg counts to identify gastrointestinal nematode resistance in a context of low-level infection of sheep on farms in eastern Algeria

The efficacy of benzimidazoles and ivermectin was tested in 14 pilot farms in eastern Algeria. Resistance was detected in strongyle nematodes against benzimidazoles (five farms) and ivermectin (one farm). The main genera in the region were resistant: Teladorsagia, Trichostrongylus, Marshallagia and Nematodirus. The evaluations based on FECRT (faecal egg count reduction tests) were not always consistent due to the low-level of infection, and we developed a simplified, repeated treatment strategy to investigate resistance. The results obtained with repeated treatment faecal egg counts match globally those obtained with conventional faecal egg count reduction tests. This simplified, repeated treatment method should be investigated further since it is quicker, and this could make it possible to test larger farm samplings.     

Segregation of natural and experimental gastrointestinal nematode infection in F2 progeny of susceptible Suffolk and resistant Gulf Coast Native sheep and its usefulness in assessment of genetic variation

Gastrointestinal nematode parasitism is a concern to small ruminants worldwide. Productivity has been compromised because such nematodes, particularly Haemonchus contortus, have developed resistance to available anthelmintics. Some sheep breeds and lines within breeds are relatively resistant to infection, a trait that may be useful for developing control strategies. Suffolk sheep, which are susceptible to infection, were crossed with Gulf Coast Native sheep, which are more resistant to infection, to produce F1 progeny. F1 rams were bred to F1 ewes which produced 227 F2 offspring. These F2 offspring were evaluated for variability in infection levels, based on fecal egg count (FEC) and blood packed cell volume (PCV), under two natural infection conditions (one at weaning and another after a summer grazing period) and one experimental infection. The range of both FEC and PCV was large for all three infection periods with annual variation. Overall, the range for the three infection periods, respectively, were 167-149,933, 0-31,400 and 17-114,667 eggs per gram (EPG) of feces and 8.7-37.0%, 7.3-33.0% and 8.3-36.0%. This segregation of infection is what would be expected of F(2) progeny from susceptible and resistant parent breeds. Heritabilities of FEC and PCV for the three infection periods, respectively, were 0.15, 0.29 and 0.12, and 0.11, 0.22 and 0.12. Based on segregation of infection, larger heritabilities and maternal environment effects that declined after weaning, the summer natural infection was probably the best model for assessing genetic variation.     

A comparison of the effects of thiabendazole and tetramisole on liveweight gain and faecal egg count of young sheep under field conditions

A fatal syndrome occurring more commonly in low-mouthed ewes of all breeds with twin lambs at foot, 2 to 3 weeks after lambing and under nutritional stress, is described. Treatment of affected ewes was generally unsuccessful, but prevention of further serious losses was achieved by supplementary feeding, preferably with lucerne hay.