FREE SHIPPING over $40
OVER 10000 FIVE-STAR REVIEWS
5% OFF ALL SUBSCRIPTIONS
100% HAPPINESS GUARANTEE
Analyze Diet
0
Parasitology research2008; 104(3); 569-574; doi: 10.1007/s00436-008-1231-x

Probable reason why small strongyle EPG counts are returning “early” after ivermectin treatment of horses on a farm in Central Kentucky.

Abstract: Critical tests were carried out in 2008 in four yearling horses (H-2, H-4, H-10, and H-11) born and raised together on a farm (MC) in Central Kentucky. These horses were treated intraorally with ivermectin paste at the dose rate of 200 microg/kg. The main interest was to try and determine more precisely, from posttreatment (PT) worm count data, the current activity of ivermectin against small strongyles in a horse herd. These horses had been treated repeatedly with this compound and counts of small strongyle eggs per gram of feces (EPGs) of these parasites have been returning sooner than previously in field tests (Lyons et al. Parasitol Res 103:209-215, 2008a). Data from the four horses revealed that a total of 3237 (nonfactored number) specimens of small strongyles was recovered from aliquot samples of feces passed PT and in the large intestinal contents at necropsy; all specimens were examined and identified. Thirteen species of adult small strongyles were recorded. Cylicocyclus (Cyc.) insigne was the predominant species. Three of the yearlings (H-2, H-4, and H-11) were necropsied at 6 days PT with ivermectin, and removals of small strongyles were: 50%, 80%, and 36% of fourth stages (L4), respectively, and 100%, 99%, and 100% of adults, respectively. As indicated, the only incomplete removal of adults from the three horses was for H-4. They consisted of two species: (1) young Cyc. insigne (those passed in the feces were fully developed); removal of this species was 89% and (2) fully developed Cylicostephanus longibursatus; 99% were removed. The fourth yearling (H-10), necropsied at 25 days PT, harbored 19,150 adult small strongyles in the large intestinal contents. Most of the species were Cyc. insigne; all were fifth stage but not sexually mature. Comparing the percentage of adult small strongyles found at necropsy relative to the total number present (those passed in the feces and at necropsy), only 0% to 1% were in the contents of the large intestines of the three horses at 6 days PT but in 26% for horse H-10 at 25 days PT. As mentioned earlier, only a few adults were found in one horse and several L(4) in the three horses at necropsy at 6 days PT. Therefore, in horse H-10, most adults found at 25 days PT presumably developed from "young" specimens not removed by ivermectin. Thus, data from the present critical tests indicate the probable cause of the "early" return of small strongyle EPG values after ivermectin treatment in the horses in field tests on Farm MC. It seems this was the result of incomplete removal of luminal specimens (L(4) and possibly young adults), some of which matured and began laying eggs by about 4 weeks PT (Lyons et al. Parasitol Res 103:209-215, 2008a). The research also showed that ivermectin was highly effective on adult small strongyles. At necropsy, the following other species of parasites (adult) were found, but none was recovered from the feces. These were (n = number of horses infected): (1) ascarids (Parascaris equorum-n = 1), (2) tapeworms (Anoplocephala perfoliata-n = 4), and (3) pinworms (Oxyuris equi-n = 3). Immature (L4) O. equi were present in two horses and removals were 0% in one horse and 39% in the other. Eyeworms (Thelazia lacrymalis) were found in one horse at necropsy. Even though a small number of horses were used in the present research, the commonality of their background made them ideal candidates as a group for this study. This aspect helps strengthen the validity of the interpretation of the findings.
Get Full Text
Publication Date: 2008-10-18 PubMed ID: 18931857DOI: 10.1007/s00436-008-1231-xGoogle Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
LinkedInCopy
  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research investigates the reasons behind small strongyle egg counts re-appearing ‘early’ following ivermectin treatment in horses, indicating potential problems with the treatment’s efficacy. The study found that ivermectin doesn’t effectively remove all young worms, leading to their maturation and egg laying within roughly four weeks post-treatment. However, the medicine showed high efficacy against adult worms.

Methodology and Results

  • The study was conducted in 2008 on four yearling horses at a farm in Central Kentucky. These horses had been consistently treated with ivermectin, but the eggs of small strongyles were returning sooner than expected in field tests.
  • After treatment with ivermectin, samples of feces were taken and analysed. At necropsy (post-mortem examination), researchers found 3237 specimens of small strongyles, from thirteen different species, in the large intestines of the horses.
  • Three of the horses were necropsied at 6 days post-treatment. The removal rates of small strongyles varied between 36% and 80% for fourth-stage larvae and were between 99% and 100% for adult worms.
  • One horse (H-4) had incomplete removal of adults, with two species surviving: a young strain of Cylicocyclus insigne and fully developed Cylicostephanus longibursatus.
  • The fourth horse, necropsied after 25 days, harboured 19,150 adult small strongyles, most of which were not mature. The proportion of adult small strongyles found in the large intestines rose to 26% for this horse, compared to 0% – 1% for the horses necropsied earlier.
  • These findings indicate that the early reappearance of eggs in horse feces after ivermectin treatment was likely due to the incomplete removal of younger worms, which then matured to become egg-laying adults.

Efficacy of Ivermectin and Existence of Other Parasites

  • Despite the concerns, the research showed that ivermectin was highly effective in eliminating adult small strongyles.
  • Other parasites found in the horses at necropsy included ascarids, tapeworms, pinworms and eyeworms. None of these were found in the feces, which might mean that ivermectin treatment was effective against them.
  • Despite the small sample size, the common background of the horses involved in the test lends validity to the findings of the study.

Cite This Article

APA
Lyons ET, Tolliver SC, Collins SS. (2008). Probable reason why small strongyle EPG counts are returning “early” after ivermectin treatment of horses on a farm in Central Kentucky. Parasitol Res, 104(3), 569-574. https://doi.org/10.1007/s00436-008-1231-x

Publication

Parasitology research
ISSN: 0932-0113
NlmUniqueID: 8703571
Country: Germany
Language: English
Volume: 104
Issue: 3
Pages: 569-574

Researcher Affiliations

Lyons, E T
  • Department of Veterinary Science, Gluck Equine Research Center, University of Kentucky, Lexington, KY, 40546-0099, USA. elyons1@uky.edu
Tolliver, S C
    Collins, S S

      MeSH Terms

      • Administration, Oral
      • Animals
      • Anthelmintics / administration & dosage
      • Anthelmintics / therapeutic use
      • Feces / parasitology
      • Ivermectin / administration & dosage
      • Ivermectin / therapeutic use
      • Kentucky
      • Parasite Egg Count
      • Strongyle Infections, Equine / drug therapy
      • Strongyle Infections, Equine / parasitology
      • Strongyloidea / classification
      • Strongyloidea / drug effects
      • Strongyloidea / isolation & purification
      • Treatment Outcome

      References

      This article includes 22 references
      1. Equine Vet J. 2003 May;35(3):246-51
        pubmed: 12755426
      2. J Am Vet Med Assoc. 2003 Aug 15;223(4):482-5, 455
        pubmed: 12930086
      3. Vet Parasitol. 1998 Dec 15;80(1):29-36
        pubmed: 9877068
      4. Parasitol Res. 2008 Jul;103(2):287-91
        pubmed: 18470536
      5. Vet Parasitol. 2007 Apr 30;145(3-4):371-6
        pubmed: 16962243
      6. Vet Ther. 2004 Summer;5(2):105-19
        pubmed: 15468008
      7. Vet Parasitol. 1991 Jan;38(1):33-9
        pubmed: 2024428
      8. Am J Vet Res. 1977 Oct;38(10):1581-6
        pubmed: 337859
      9. Vet Parasitol. 2001 Jul 27;98(4):315-20
        pubmed: 11423189
      10. Am J Vet Res. 1963 Nov;24:1217-22
        pubmed: 14081458
      11. Vet Parasitol. 2007 Mar 15;144(1-2):74-80
        pubmed: 17112667
      12. Am J Vet Res. 1981 Jun;42(6):1046-7
        pubmed: 7197131
      13. Vet Rec. 2007 Mar 31;160(13):439-40
        pubmed: 17400903
      14. Vet Rec. 1987 Mar 28;120(13):293-6
        pubmed: 3590562
      15. Parasitol Res. 2008 Jun;103(1):209-15
        pubmed: 18389281
      16. J Am Vet Med Assoc. 2004 Sep 15;225(6):903-10
        pubmed: 15485051
      17. Vet Parasitol. 1994 May;53(1-2):83-90
        pubmed: 8091622
      18. Am J Vet Res. 1982 Aug;43(8):1451-3
        pubmed: 6896613
      19. Vet Rec. 2002 Mar 2;150(9):279-81
        pubmed: 11924584
      20. Vet Parasitol. 1999 Aug 31;85(2-3):97-111; discussion 111-2, 215-25
        pubmed: 10485357
      21. Vet Parasitol. 1992 May;42(3-4):295-302
        pubmed: 1496789
      22. Parasitol Res. 2006 Apr;98(5):496-500
        pubmed: 16385405

      Citations

      This article has been cited 20 times.
      1. Elghryani N, Lawlor A, McOwan T, de Waal T. Unravelling the Effectiveness of Anthelmintic Treatments on Equine Strongyles on Irish Farms. Animals (Basel) 2024 Jul 2;14(13).
        doi: 10.3390/ani14131958pubmed: 38998069google scholar: lookup
      2. Macdonald SL, Abbas G, Ghafar A, Gauci CG, Bauquier J, El-Hage C, Tennent-Brown B, Wilkes EJA, Beasley A, Jacobson C, Cudmore L, Carrigan P, Hurley J, Beveridge I, Hughes KJ, Nielsen MK, Jabbar A. Egg reappearance periods of anthelmintics against equine cyathostomins: The state of play revisited. Int J Parasitol Drugs Drug Resist 2023 Apr;21:28-39.
        doi: 10.1016/j.ijpddr.2022.12.002pubmed: 36543048google scholar: lookup
      3. Nielsen MK. Anthelmintic resistance in equine nematodes: Current status and emerging trends. Int J Parasitol Drugs Drug Resist 2022 Dec;20:76-88.
        doi: 10.1016/j.ijpddr.2022.10.005pubmed: 36342004google scholar: lookup
      4. Dauparaitė E, Kupčinskas T, Hoglund J, Petkevičius S. A Survey of Control Strategies for Equine Small Strongyles in Lithuania. Helminthologia 2021 Sep;58(3):225-232.
        doi: 10.2478/helm-2021-0031pubmed: 34934386google scholar: lookup
      5. Dauparaitė E, Kupčinskas T, von Samson-Himmelstjerna G, Petkevičius S. Anthelmintic resistance of horse strongyle nematodes to ivermectin and pyrantel in Lithuania. Acta Vet Scand 2021 Jan 25;63(1):5.
        doi: 10.1186/s13028-021-00569-zpubmed: 33494770google scholar: lookup
      6. Scala A, Tamponi C, Sanna G, Predieri G, Dessì G, Sedda G, Buono F, Cappai MG, Veneziano V, Varcasia A. Gastrointestinal Strongyles Egg Excretion in Relation to Age, Gender, and Management of Horses in Italy. Animals (Basel) 2020 Dec 3;10(12).
        doi: 10.3390/ani10122283pubmed: 33287298google scholar: lookup
      7. Nielsen MK, Banahan M, Kaplan RM. Importation of macrocyclic lactone resistant cyathostomins on a US thoroughbred farm. Int J Parasitol Drugs Drug Resist 2020 Dec;14:99-104.
        doi: 10.1016/j.ijpddr.2020.09.004pubmed: 33022574google scholar: lookup
      8. Tinkler SH. Preventive chemotherapy and anthelmintic resistance of soil-transmitted helminths - Can we learn nothing from veterinary medicine?. One Health 2020 Jun;9:100106.
        doi: 10.1016/j.onehlt.2019.100106pubmed: 31956691google scholar: lookup
      9. Leathwick DM, Sauermann CW, Nielsen MK. Managing anthelmintic resistance in cyathostomin parasites: Investigating the benefits of refugia-based strategies. Int J Parasitol Drugs Drug Resist 2019 Aug;10:118-124.
        doi: 10.1016/j.ijpddr.2019.08.008pubmed: 31491731google scholar: lookup
      10. Hernández JÁ, Sánchez-Andrade R, Cazapal-Monteiro CF, Arroyo FL, Sanchís JM, Paz-Silva A, Arias MS. A combined effort to avoid strongyle infection in horses in an oceanic climate region: rotational grazing and parasiticidal fungi. Parasit Vectors 2018 Apr 12;11(1):240.
        doi: 10.1186/s13071-018-2827-3pubmed: 29650055google scholar: lookup
      11. Molena RA, Peachey LE, Di Cesare A, Traversa D, Cantacessi C. Cyathostomine egg reappearance period following ivermectin treatment in a cohort of UK Thoroughbreds. Parasit Vectors 2018 Jan 25;11(1):61.
        doi: 10.1186/s13071-018-2638-6pubmed: 29370872google scholar: lookup
      12. Dibaba MD, Getachew AM, Assefa Z, Fanta A, Etana M, Firew S, Goshu L, Burden F. Seasonal variation of strongylosis in working donkeys of Ethiopia: a cross-sectional and longitudinal studies. Parasitol Res 2017 Jul;116(7):2009-2015.
        doi: 10.1007/s00436-017-5485-zpubmed: 28536880google scholar: lookup
      13. Matthews JB. Anthelmintic resistance in equine nematodes. Int J Parasitol Drugs Drug Resist 2014 Dec;4(3):310-5.
        doi: 10.1016/j.ijpddr.2014.10.003pubmed: 25516842google scholar: lookup
      14. Schneider S, Pfister K, Becher AM, Scheuerle MC. Strongyle infections and parasitic control strategies in German horses - a risk assessment. BMC Vet Res 2014 Nov 12;10:262.
        doi: 10.1186/s12917-014-0262-zpubmed: 25387542google scholar: lookup
      15. Lyons ET, Tolliver SC. Further indication of lowered activity of ivermectin on immature small strongyles in the intestinal lumen of horses on a farm in Central Kentucky. Parasitol Res 2013 Feb;112(2):889-91.
        doi: 10.1007/s00436-012-3098-0pubmed: 22948206google scholar: lookup
      16. Lyons ET, Tolliver SC, Collins SS. Reduced activity of moxidectin and ivermectin on small strongyles in young horses on a farm (BC) in Central Kentucky in two field tests with notes on variable counts of eggs per gram of feces (EPGs). Parasitol Res 2011 May;108(5):1315-9.
        doi: 10.1007/s00436-010-2225-zpubmed: 21212983google scholar: lookup
      17. Becher AM, Pfister K. [The efficacy of anthelmintic drugs against horse strongyles in the area of Salzburg and preliminary results of selective anthelmintic treatment]. Wien Klin Wochenschr 2010 Oct;122 Suppl 3:71-5.
        doi: 10.1007/s00508-010-1441-ypubmed: 20924696google scholar: lookup
      18. Lyons ET, Tolliver SC, Collins SS, Ionita M, Kuzmina TA, Rossano M. Field tests demonstrating reduced activity of ivermectin and moxidectin against small strongyles in horses on 14 farms in Central Kentucky in 2007-2009. Parasitol Res 2011 Feb;108(2):355-60.
        doi: 10.1007/s00436-010-2068-7pubmed: 20862493google scholar: lookup
      19. Lyons ET, Tolliver SC, Kuzmina TA, Collins SS. Critical tests evaluating efficacy of moxidectin against small strongyles in horses from a herd for which reduced activity had been found in field tests in Central Kentucky. Parasitol Res 2010 Nov;107(6):1495-8.
        doi: 10.1007/s00436-010-2025-5pubmed: 20714749google scholar: lookup
      20. Nielsen MK. Restrictions of anthelmintic usage: perspectives and potential consequences. Parasit Vectors 2009 Sep 25;2 Suppl 2(Suppl 2):S7.
        doi: 10.1186/1756-3305-2-S2-S7pubmed: 19778468google scholar: lookup
      Subscribe to our newsletter
      Join 99,780 horse owners like you who receive our email updates on horse health and nutrition.