Effect of Duddingtonia flagrans against Ostertagia ostertagi in cattle grazing at different stocking rates

The efficacy of an isolate of the nematophagous fungus Duddingtonia flagran s against gastrointestinal nematodes of cattle was examined at 2 dose level s on 2 permanent pastures, with high and low stocking rates, respectively. Thirty calves, experimentally infected with Ostertagia ostertagi, were divi ded into 3 comparable groups and allocated to 3 similar paddocks in each of the 2 trials. Two of the 3 groups received fungal material once per day du ring the initial 2 months, either at high dose (10(6) fungal spores/kg body weight) or low dose (5 x 10(5) or 2.5 x 10(5) fungal spores/kg body weight ). The third group remained as an untreated control group. Faecal, blood, a nd herbage samples were collected and animals were weighed every month from May to September. The pasture prated at a high stocking rate had a large n umber of overwintering infective larvae, while the pasture grazed at a lon stocking rate had a low overwintering herbage larval infectivity. The resul ts showed that, at a high stocking rate, the recovery of infective larvae o n pasture was diminished and calves were prevented from clinical ostertagio sis by using the D. flagrans Troll A-isolate. At low stocking rate, the par asite burden seemed not to be very heavy, and a conclusive effect of the fu ngi at the dose-level used could not be detected.