Are Respiratory Clinical Signs in Horses Associated With Strongyle Egg Shedding Rates on Farms With Varying Egg Shedding Levels?

Respiratory signs or more specifically severe equine asthma (SEA) is in some studies reported to be associated with decreased strongyle egg shedding. This association can be reproduced in a larger population of unrelated horses. The owners of 209 horses, on seven farms in Bavaria, were interviewed using, an in prior studies validated questionnaire. Horses were categorized into classes of the horse owner assessed respiratory signs index (HOARSI 1-4, unaffected to severely affected). In total, 1,035 fecal samples were analyzed between March 2011 and September 2014 using a modified McMaster procedure resulting in fecal egg counts (FECs). The HOARSI categories were categorized into two groups in two ways: HOARSI 1 versus HOARSI 2, 3, 4 in model A and HOARSI 1 versus HOARSI 3 and 4 in model B, and further variables known to influence strongyle egg shedding, such as age and seasonality, time on pasture, and pasture hygiene were included in a generalized additive mixed model. The mean FECs (35-320 eggs per gram feces) was different between the farms. In the model, the effect of the presence or absence of respiratory signs on the FECs varied in its direction between the farms and was not significant. The effect of the horse itself, the age of the horse, and seasonality was significant (P < .05). These results are in contrast to some prior studies. Future studies should investigate if these differences are caused by genetic effects only present in some respiratory clinical signs and or SEA-affected horses.

Repeatability of strongyle egg counts in naturally infected horses.

The selective treatment of horses is used to decrease the number of anthelmintic treatments by only treating a proportion of animals in the population. One way to select animals for treatment is to identify low and high egg-shedders using faecal egg counts (FEC); then to treat only the high egg-shedders. The value of this method is enhanced if differences among individuals in the level of egg-shedding remain consistent over time. One way to assess the stability of the rankings of animals over time is to measure the repeatability which is defined as the variance between horses divided by the total variance. The repeatability varies between 0 (no consistency in the values) to 1 (perfect consistency). To determine the repeatability of egg-shedding in naturally infected horses over time, 2637 FEC and raw egg counts (REC; i.e. originally counted eggs without multiplication factor) from 303 horses were analysed. The distribution of FEC was more overdispersed than a Poisson distribution. Therefore, a negative-binomial model was used. The within-horse-repeatability of RECs was 0.52. In a second analysis, we excluded horses that were treated with anthelmintic drugs during the study by eliminating all REC within the egg-reappearance-period. Here, the within-horse-repeatability was very similar at 0.53. The results show that egg-shedding of individual horses stays fairly consistent over time. They also show that animals which shed relatively high numbers of nematode eggs can be identified and targeted for treatment.

Strongyle infections and parasitic control strategies in German horses - a risk assessment.

BACKGROUND: As a consequence of the increasing levels of anthelmintic resistance in cyathostomes, new strategies for equine parasite control are being implemented. To assess the potential risks of these, the occurrence of strongyles was evaluated in a group of 1887 horses. The distribution of fecal egg counts (FECs), the frequency of anthelmintic drug use, and the deworming intervals were also analyzed. Between June 2012 and May 2013, 1887 fecal samples from either selectively or strategically dewormed horses were collected at 195 horse farms all over Germany and analyzed quantitatively with a modified McMaster technique. All samples with FEC ≥20 eggs per gram (EPG) were subjected to coproculture to generate third-stage larvae (LIII) for species differentiation. RESULTS: Egg counts were below the limit of detection (20 EPG) in 1046 (55.4%) samples and above it in 841 (44.6%) samples. Strongylus vulgaris larvae were identified in two of the 841 positive samples. Infections with cyathostomes were found on every farm. The most frequently applied anthelmintic was ivermectin (788/50.8%), followed by pyrantel (336/21.6%). The mean time since last treatment was 6.3 months. High-egg-shedding (>500 EPG) strategically dewormed horses (183/1357) were treated, on average, three times/year. The planned treatment date was already exceeded by 72.5% of the high egg-shedders and by 58.1% of the moderate (200-500 EPG) and low egg-shedders (20-199 EPG). CONCLUSIONS: S. vulgaris seems to be rare in Germany and no difference in its frequency has yet been found between selectively treated horses and horses receiving treatment in strategic intervals. However, inconsistent parasite control has been observed. Therefore, to minimize the risks for disease, consistent and efficient parasite control should be implemented.

[The efficacy of anthelmintic drugs against horse strongyles in the area of Salzburg and preliminary results of selective anthelmintic treatment]. / Wirksamkeit von Anthelminthika gegenüber Pferdestrongyliden im Raum Salzburg und erste Ergebnisse der selektiven Behandlung.

In recent years more and more cases of anthelmintic resistant equine strongyles were reported. The latest developments are cases of resistance against macrocyclic lactones. In order to delay this process less anthelmintics and only those which have been previously tested for their efficacy on each individual farm should be used. During the grazing season 2008 faecal samples of 281 horses and 5 donkeys from 26 farms were analysed in the area of Salzburg. To 164 of these horses selective anthelmintic treatment was implemented. Every four weeks faecal samples from the 164 horses were quantitatively analysed for strongyle eggs using a modified McMaster technique. When more than 250 eggs per gram (EpG) of faeces were detected in a sample the horse was treated with an oral pyrantel product. In case of a subsequent faecal sample of the same horse with EpG > 250, Ivermectin, and after the third sample with EpG > 250, Moxidectin was administered. In the fall 2008, all 164 horses together with 117 additional horses and 5 donkeys were treated with Moxidectin plus Praziquantel independent of the faecal egg count. After each anthelmintic treatment a faecal egg count reduction test was performed. In total 1521 faecal samples were analysed. In 1065 samples (70%) no strongyle eggs were detected at all and only 109 samples (7%) had EpG > 250 values. After the treatment with Pyrantel a total of 49 faecal egg count reduction tests, after the treatment with Ivermectin 28 and after the administration of Moxidectin totally 109 faecal egg count reduction tests were performed. After the treatment with either Ivermectin or Moxidectin, all faecal egg count reductions were 100%. On one farm however, the mean reduction of strongyle eggs after the administration of pyrantel was 85.4% on day 14 and 74.9% on day 21. Therefore, faecal egg count reduction tests are strongly recommended whenever horses are treated with Pyrantel.