Effect of spraying Arthrobotrys conoides conidia on pastures to control nematode infection in sheep

Resumo

The effect of spraying pastures with conidia of the fungus Arthrobotrys conoides (GenBank ID: JN191309) for the biological control of gastrointestinal nematode infection-pressure in lambs was assessed. A 12,000-m2 area was divided into six 2,000-m2 fenced areas. Two groups were formed: the treatment group comprised three fenced areas, where conidia were sprayed on the pasture weekly at 7.5 x 104 conidia m-2; and the control group, also comprising three fenced areas, where conidia were not sprayed. The pastures included lopsided oat (Avena strigosa Schreb) and Italian ryegrass (Lolium multiflorum Lam.). Five naturally infected lambs, were placed between July and September in each fenced area. The effectiveness of biological control was assessed between May and September 2009 by counting the number of third-stage larvae (L3) in each pasture. Additionally, the egg output of the sentinel animals was monitored by counting the number of gastrointestinal nematode eggs per gram of faeces (EPG) and the average weight gain was measured. The negative impact on soil was assessed by counting the number of free-living nematodes and phytonematodes. The number of gastrointestinal nematode larvae in the treated pastures decreased. This was significant at two examination days (end August and end of September). At the end of the study, conidia treatment reduced gastrointestinal nematodes on pasture by 52.4% compared to the control group; this difference was statistically significant. Regarding the whole examination period the average reductions in EPG in treatment group was 49.1% compared to the control group. The most common genera of gastrointestinal nematodes were Haemonchus and Trichostrongylus. Animal weight gain and soil nematode counts did not differ significantly.