, 1981). The in vitro

methods provide means to screen rapidly for potential anthelmintic activities of different plant extracts and to analyze the possible mechanisms involved in the interactions between active compounds and parasites. C. schoenanthus showed the best anthelmintic activity in vitro. Thus, based on the LC50 of 24.66 mg/ml obtained for C. schoenanthus in LEA, an approximate dose of 1.18–2.45 g of oil/kg STI571 in vitro body weight (BW) would provide a 50% reduction in exsheathment and worm reduction considering an animal of 40 kg and 2–4l abomasal volume. However, sometimes the effect in vitro or in a different animal system can be lower than when tested in the target host. A recent illustration of this point is the work with orange emulsion oil, where 600 mg of the oil emulsion per kg BW caused 7% and PLX3397 cost 62.6% worm reduction in gerbils with a single dose or daily for five days, respectively ( Squires et

al., 2010). However, when these authors tested the emulsion with 600 mg of orange oil per kg BW in sheep infected with H. contortus, it resulted in a 97.4% reduction in fecal egg count (adult worm reduction was not evaluated). Although encouraging, these results must be interpreted with caution because of the high doses of the preparation (40% orange terpenes, 20% Valencia orange oil, 4% polysorbate 80, and 1.5% hydrogen peroxide) required for anthelmintic effects. The authors Tolmetin mentioned that few lambs presented toxicity signs such as head shaking and feed aversion. These symptoms may be aggravated if the active component(s) has(ve) a low LD50. In the case of the orange oils used, the authors ( Squires et al., 2010) reported that >95% was d-limonene, which has a high LD50 (5000 mg/kg). When a potential compound or plant extract is found, more comprehensive studies are needed

to assess its bioavailability. How much is being absorbed and metabolized versus how much is being disposed in gastrointestinal content, and which metabolites are being generated. Besides nematocidal effect, plant extracts/compounds are tested for their ability to impair egg hatching and larval development from feces of infected animals treated with those plant extracts. Desired effects can result in reduced re-infection and lighter worm loads leading to decreased pasture contamination levels (Ketzis et al., 2002 and Max, 2010). In vivo tests, problems with absorption through the gastrointestinal tract, and compound solubility and stability after oral intake are the main obstacles in developing herbal formulations with good bioavailability and anthelmintic efficacy. According to Stepek et al. (2007), given the sensitivity to pH, it is not surprising that plant enzymes for instance have lower efficacy against stomach nematodes in situ than against those residing further down the gastrointestinal tract.