Development of an in vitro test to compare natural and chemical products effectiveness against Ls gastrointestinal strongylids of sheep

Gastrointestinal nematodes are still one of the main constraints to sheep production. The rising resistance to anthelmintic drugs and the increasing interest for organic livestock products have drawn attention for the use of natural drugs. In this study we perform an in vitro method to evaluate the effectiveness of several natural products, compared to some chemicals, against the third larval stage (L3) of gastrointestinal strongylids of ruminants. L3 obtained from sheep faecal cultures were distributed in 24- wells plates with serial dilutions of the testing products. To evaluate the larvicidal activity of the candidate drugs, the number of surviving larvae was counted after 24, 48 hours and 7, 14, 21, 28 days. The mean number of surviving larvae was compared according to the different products tested at various concentrations and at different contact time, and statistical analyses were performed. In this study, a dry extract of leaves of Neem (Azadirachta indica), essential oils of Oregano (Origanum vulgare), Lemon (Citrus limon) and Rosemary (Rosmarinus officinalis), Levamisole and Calcium cyanamide nitrate were tested. After 24 hours, Levamisole > 2,5 ppm, Calcium cyanamide > 5000 ppm and Oregano essential oil > 5000 ppm concentrations killed all the larvae. Neem caused total death of larvae at > 10000 ppm after 7 days, but after 24 hours the number of surviving larvae was significantly lower than the control. Rosemary and Lemon essential oils were not effective. This method, easy to perform and replicable, can be used as screening to assess the effectiveness of different products against the L3 of gastrointestinal strongylids. Further experiments are necessary in order to better understand the real effectiveness on the field.