Occurrence, diagnosis and control of gasterophilosis in horses

Between September 1994 and May 1998 physical, gastroscopical and postmortal examinations were carried out to investigate occurrence, prevalence and in vasion intensity of Gasterophilus sp. in horses mainly in Saxonia. Botfly e ggs were found on preferred body areas in 38 (30.9 %) of 123 horses examine d. In the period from August to November both unembryonated and embryonated botfly eggs were seen, and from August to February also egg sheats deposit ed on the hair were detected. Gastroscopically larvae clearly distinguishab le in second- and third-instars were found in the stomach of 40 (21.1%) out of 190 horses. Second-instar larvae were present in the stomach from the b eginning of September to mid of December but third instars from the beginni ng of September to August in the following year. From September 1994 to May 1998 post mortem examinations were performed on 87 horses, 40 (46 %) of th em showed low(< 20 larvae/stomach, 52.5 %), moderate (20 - 100 larvae/stoma ch, 45 %) or severe (>100 larvae/stomach, 2.5 %) infestation with Gasteroph ilus intestinalis larvae. The period recommended for treatment with ivermec tin or metrifonate against larvae of Gasterophilus intestinalis is the seco nd half of November.