In vitro, field, and in vivo trials of Metarhizium anisopliae isolate IBCB425 against Haemonchus contortus

Abstract

The fungus Metarhizium anisopliae IBCB425 was tested against Haemonchus contortus in several trials. Coprocultures containing approximately 10,000 H. contortus eggs were inoculated with 10⁵, 10⁶, 10⁷, 10⁸, and 10⁹ conidia and a control. After ten days at room temperature, larvae were recovered, counted, and checked for motility. Treatment with 10⁸ and 10⁹ conidia reduced larval recovery, and all concentrations diminished motility compared with the control (p < 0.05). Subsequently, parcels demarcated on an animal-free paddock were artificially contaminated with 80,000 H. contortus eggs and were sprayed twenty days later with 10⁹, 10¹⁰, and 10¹¹ conidia/m² and a control. After thirty days, grass samples were collected to recover larvae and analyze dry matter (DM). Spraying with 10¹¹ conidia/m² reduced motility compared with the control (p < 0.05). Later, two parcels were demarcated on a naturally infected paddock grazed by mixed-breed sheep. One parcel was sprayed with 2 × 10¹³ conidia/ha, and the other served as control. Treatment was applied five times at 30 – 45 days intervals, from May to October. Before spraying, grass samples were collected to recover nematodes and calculate DM. No treatment-related effects were observed. Then, these parcels were fenced, and tracer groups, blocked according to age, sex, and fecal egg count (FEC), were allocated to each parcel and grazed for 35 days when males were slaughtered. No effects were detected on FECs and abomasal worm burdens. Coprocultures from both groups yielded moldy larvae, which might indicate gut survival.