Livestock is an important prospective sector which may contribute in solving problems of small farmers and by such, help in poverty alleviation [1] . Small ruminants particularly goats have been considered the most important aspect of livestock throughout the world. In 2010, world caprine livestock counted 920 million animals, with more than 90% in Asia and Africa [2] . In Cameroon, Labonne et al. [3] registered 7 million goats, with half of this population concentrated in the Extreme-North Region. Parasitism by gastro-intestinal nematodes (GINs) is a major constraint in the production of goats in tropical countries. They can affect production through weight loss, diarrhea, anemia, reduction in milk and wool production, reproduction changes as well as mortality in the case of heavy infectations [4] . Actually, a majority of nematodes affecting the intestinal tract of small ruminants belong to the Order Strongylidae, with principal genera being Haemonchus, Teladorsagia, Cooperia, Trichostrongylus, Nematodirus, Chabertia and Œsophagostomun [5] . Compared to other nematodes, H. contortus is by far a highly pathogenic parasite of small ruminants, capable of causing acute disease and high mortality in all classes of livestock [6] . Up to now, a huge amount of money is spent annually worldwide to combat helminth parasites in livestock, the principal mode of control being based on the repeated use of commercial anthelminthic drugs such as levamisol, morantel, thiabendazole, mebendazole, albendazole, ivermectin and dormactin. However, nematodes have developed resistance against several families of anthelminthics. Moreover, toxicity due to inappropriate dose administration and risk of drug residues in animal products are other big problems associated with the use of synthetic drugs [7] . In most developing countries like Cameroon, small holder farmers have limited access to such drugs and veterinary services due to either high cost or unavailability. Therefore, most of the farmers rely on ethno-veterinary treatment. Medicinal plants are considered as an alternative source of compounds that are biodegradable into non-toxic products and sustainable methods readily adaptable to rural farming communities. Moringa oleifera is considered as one of the most useful trees as almost every part can be used for food or has some other beneficial properties. In the tropics, it is used as forage for livestock and in many countries; it is used to treat various ailments [8] . In Cameroon, M. oleifera is used to treat asthma, anemia, intestinal worms, cardio-vascular disorder, headache, skin infections and others (personal communication). Extracts from this plant have several pharmacological effects such as anthelminthic, anti-inflammatory, anti- microbial, anti-oxydant, hepato-protective, anti-glycemic and anti-dislipidemia [8] -[13] . As far as literature on this plant is concerned, there is no published work on in vitro anthelminthic activity of Moringa oleifera against Haemonchus contortus. The aim of the present study was thus to investigate the in vitro activities of aqueous and ethanolic leaf extracts of M. oleifera on four free-living stages of H. contortus from goats.

Comparison of the mean inhibition percentage of egg embryonation, mean inhibition percentage of egg hatch and mean percentage of larval mortality at different concentrations with control was performed by one-way analysis of variance (ANOVA). Statistical analysis was performed by using the software SPSS version 17.0. The post hoc statistical significance test employed was Duncan, differences between the means were considered significant at P < 0.05. The 50% inhibitory concentration (IC₅₀) and lethal concentration (LC₅₀), i.e., effective concentration to inhibit 50% of the eggs and to kill 50% of larvae were determined using the regression lines of the probit according to decimal logarithm of the concentrations.

Efficacy of M. oleifera leaf extracts in inhibiting egg embryonation of Haemonchus contortus at different concentrations is presented in Table 1. From this table, we observed that negative controls (distilled water and 1.5% distilled water) had no effect on egg embryonation while M. oleifera extracts inhibited embryonation in a concentration dependent fashion. Ethanolic extract was efficient at 0.625 mg/ml by inhibiting 51.7% ± 20.7% egg embryonnation, reaching 92.8% ± 6.2% at 5 mg/ml with a significant difference (P < 0.05). Infused and macerated aqueous extracts also inhibited embryonation with mean efficacy of 69% ± 5.8% and 94.5% ± 4% at 5 mg/ml respectively. The IC₅₀s calculated from equations of regression lines of probit according to the decimal logarithm of concentrations (Figure 1) were 2.52, 1.52 and 0.985 mg/ml for macerated, infused aqueous extract and ethanolic extract respectively.

Table 2 shows activity of extracts in inhibiting egg hatch of H. contortus at different concentrations. Like on embryonation, distilled water and 1.5% DMSO did not affect egg hatch while extracts presented a concentration

Letters compare means in the columns. Different letters indicate significant difference (P < 0.05). Legend: MIAE = Moringa oleifera infused aqueous extract, MMAE = Moringa oleifera macerated aqueous extract, MEtE = Moringa oleifera ethanolic extract, sd = standard deviation, DW = Distilled water, DMSO = Dimethylsulfoxide, NA = Not applicable.

Letters compare means in the columns. Different letters indicate significant difference (P < 0.05). Legend: MIAE = Moringa oleifera infused aqueous extract, MMAE = Moringa oleifera macerated aqueous extract, MEtE = Moringa oleifera ethanolic extract, sd = standard deviation, DW = Distilled water, DMSO = Dimethylsulfoxide, NA = Not applicable.

dependent activity. Macerated aqueous extract and ethanol extract inhibited more than 60% egg hatch at 2.5 mg/ml, reaching 90.2% ± 8.4% and 99% ± 2% at 5 mg/ml respectively. The infused aqueous extract inhibited 69.2% ± 17.1% and 97.9% ± 4.2% egg hatch at 3.75 and 5 mg/ml respectively with a significant difference (P < 0.05). IC₅₀s values of 2.37, 1.75 and 1.74 mg/ml were obtained for macerated, infused and ethanolic extracts respectively from equations of regression lines of the probit of egg hatch inhibition according to decimal logarithm of concentrations (Figure 2).

Concerning larvicidal activity, Table 3 and Table 4 present the efficacy of M. oleifera extracts in inducing L₁ and L₂ larva mortality at different concentrations respectively. From Table 3, infused aqueous extract showed weak activity on L₁ larvae, inducing only 50.5% ± 8.8% mortality at 5 mg/ml. However, macerated aqueous extract induced 89.6% ± 8.8% at 5 mg/ml while at the same concentration ethanolic extract registered 98.8% ± 2.5% L₁ larva mortality. LC₅₀s values of L₁ larvae calculated from equations of regression lines (illustrated on Figure 3) were 7.83, 2.92 and 1.89 mg/ml for infused, macerated aqueous extracts and ethanolic extract respectively.

Letters compare means in the columns. Different letters indicate significant difference (P < 0.05). Legend: MIAE = Moringa oleifera infused aqueous extract, MMAE = Moringa oleifera macerated aqueous extract, MEtE = Moringa oleifera ethanolic extract, sd = standard deviation, DW = Distilled water, DMSO = Dimethylsulfoxide, NA = Not applicable.

Letters compare means in the columns. Different letters indicate significant difference (P < 0.05). Legend: MIAE = Moringa oleifera infused aqueous extract, MMAE = Moringa oleifera macerated aqueous extract, MEtE = Moringa oleifera ethanolic extract, sd = standard deviation, DW = Distilled water, DMSO = Dimethylsulfoxide, NA = Not applicable.

As seen from Table 4 the ethanolic extract was most efficient in inducing 98.8% ± 3.1% and 100% ± 0% L₂ larva mortality at 3.75 and 5 mg/ml respectively, with no significant difference (P ˃ 0.05). At these same concentrations, aqueous extracts also induced L₂ mortality even though the mean mortality rates were lower than those obtained with ethanolic extract. LC₅₀s values of L₂ larvae calculated from equations of regression lines (illustrated on Figure 4) were 3.57, 2.08 and 1.5 mg/ml for infused, macerated aqueous extract and ethanolic extract respectively. Like on eggs, distilled water and 1.5% DMSO had no effect on larvae while M. oleifera extracts were active in a concentration dependent manner.

In developing countries, the identification of a plant with anthelminthic property may help to build an integrated and sustainable approach for the control of gastro-intestinal nematodes in small ruminants. The objective of this study was to evaluate in vitro ovicidal and larvicidal efficacy of aqueous and ethanolic leaf extracts of

M. oleifera against H. contortus. In vitro bioassay provides means to rapidly screen for plant extracts and to analyze the possible mechanisms involved in the interactions between active compounds and parasites [19] . Asase et al. [20] reported that in vitro tests using free living stages of parasitic nematodes as is the case in the present study are considered the best means of screening the anthelminthic activity of new plant compounds. In this study, M. oleifera leaf extracts presented a concentration-dependent activity against the four different free-living stages of H. contortus, suggesting that increase in concentration of plant extract is followed by a supplementary input of different active compounds. Infused aqueous extract and ethanolic extract of M. oleifera presented comparable activity on eggs. The first extract (infused) inhibited 69% ± 1% and 97.9% ± 4.2% of egg embryonation and egg hatch at 5 mg/ml with IC₅₀s values of 1.52 and 1.75 mg/ml respectively. While the latter (ethanolic) inhibited 92.8% ± 6.2% and 99% ± 2% of egg embryonation and egg hatch at 5 mg/ml, with IC₅₀s values of 0.985 and 1.74 mg/ml respectively. Tatik and Dwatmadji [21] recorded the same observation between crude aqueous and ethanolic extracts of Melastoma malabatricum on eggs of H. contortus. They also found out that there was no statistically significant difference in the activity of aqueous and hydro-alcoholic extracts of Hedera helix after evaluation of in vitro anthelminthic activity against H. contortus. The observed uniform activity of infused aqueous extract and ethanolic extract of M. oleifera on eggs could be due to the presence of similar or related chemicals having ovicidal property in nearly equivalent proportions. Based on LC₅₀s values, ethanolic extracts presented the highest larvicidal activity since it registered the lowest values of 1.89 and 1.5 mg/ml on L₁ and L₂ larvae respectively. These LC₅₀s values revealed that L₁ larvae were more susceptible to ethanolic extract than L₂ larvae, confirming the literature findings of Soulby [22] and could be explained by the fact that since L₂ are just from the process of molting, they are still weak and more vulnerable to active compounds [23] . However, Wabo Poné et al. [24] found opposite results when evaluating in vitro activities of acetonic extracts of leaves of three forage legumes on H. contortus, since they obtained LC₅₀s values below 0.9 and above 1 mg/ml for L₁ and L₂ larvae respectively. Infused aqueous extract generally exhibited higher activity on eggs than on larvae. Macerated aqueous extract showed a good activity on almost all the four stages of parasites. The probable reason for the minor differences between aqueous and ethanolic extracts could be due to variation in solubility of the active compounds in the solvent. The ovicidal and larvidal activities observed in this study with different extracts may be attributed to the presence of saponins, steroids, carbohydrates, alkaloids, tannins, flavonoids which were previously reported to be present in leaves of M. oleifera after preliminary phytochemical screening [25] . These secondary metabolites may take the two ways of anthelminthic drugs that are diffused through egg shells or cuticle of larvae or diffusion into intestinal cells to exert their inhibition or mortality action on eggs and larvae of H. contortus.

In conclusion, the activity from this study shows the potential value of Moringa oleifera leaf extracts in the management of haemonchosis, since inhibition of egg embryonation, egg hatch and mortality of L₁ and L₂ larvae are important in reducing pasture contamination thereby helping in the overall helminth control programme. However, in order to use this plant for better beneficial purpose in the fight against gastro-intestinal nematodes, further in vivo and toxicity studies are necessary.

The authors are grateful to the Laboratory of Biology and Applied Ecology (LABEA) of University of Dschang-Cameroon where this study was carried out. They also like to thank the Dean of the Faculty of Agronomy and Agricultural Sciences (FAAS) of University of Dschang for allowing access into Teaching and research farm of the University of Dschang.