Coprological analysis allow the identification of parasitism of ruminants by trychostrongylid but not to species level. In order to know species implicated eggs must be cultured and larvae must develop on coproculture and mature to infective stage of L3. In this work we studied the variability of the third larval stage of a local Haemonchus contortus strain obtained from a local sheep herd in Gran Canaria island (Spain), focusing on the three parameters used for species identification: total length, sheath length and filament length, comparing the mean lengths of the local larvae strain with those described in other studies. In addition, we wondered if larva lengths could vary as a consequence of the different immunological response developed by sheep through the infection and also between lambs with no history of previous infection. Significant differences have been observed between larvae and between animals at each time point, as well as significant differences within animals over time. The larvae were 3.7-0.7% shorter at week 4 within the animals, which could indicate that the immune response of the sheep may influence the length of L3. However, culture conditions also may influence the development and size of the larvae and further studies are needed in order to confirm it.