Biological variations in fenbendazole resistant and susceptible strains of Haemonchus contortus in sheep

A study was conducted to assess the biological variations in fenbendazole resistant and susceptible strains of Haemonchus contortus in three groups of lambs comprising of 6 lambs each. Lambs of group I and group II were experimentally infected with susceptible and resistant strain of H. contortus, respectively, while those of group III were kept as uninfected control. The prepatent period infection was 18 days in both the infected groups. The fecundity as measured by mean faecal egg counts was significantly higher in resistant strain than susceptible strain. Lambs of group II infected with resistant strain were more anaemic on the day 15 to 45 as measured by mean haemoglobin (Hb) concentration and mean packed cell volume (PCV%) and also induced comparatively more hypoproteinaemia than produced by susceptible strain in lambs of group I. The infectivity and establishment rate was higher in lambs infected with resistant strain.