Abstract The nematodes of the genus Oesophagostomum Molin, 1861 parasitize in the large intestine of ruminants and are widely represented in the terrestrial ecosystems of many countries of the world. One of the most common species of this genus in small ruminants is Oesophagostomum venulosum Rudolphi, 1809. The validity of this species was established using morphological and molecular genetic methods, the importance of which is still relevant. The aim of our research was to determine the morphological and metric characteristics of O. venulosum nematodes isolated from domestic goats in Ukraine. The differential parameters of mature males and females of nematodes of this species are described and illustrated, and the obtained data is analyzed in the context of the findings of other authors. The taxonomic morphological characters of O. venulosum include the presence of a pronounced cuticular vesicle at the head end, inner and external corona radiata, cervical papillae located behind the esophagus; in males, the presence of prebursal papillae in front of the tail bursa and features of its structure, thin and tubular spicules and features of the structure of their proximal and distal ends; in females, features of the structure of the tail end, vulva and its location. 35 morphometric indicators were determined and proposed to be used in the identification of O. venulosum in males, and 29 indicators in females. Of these, 20 parameters characterize the general body structure (the length and width of the nematode, the dimensions of the mouth capsule, cervical vesicle, esophagus, the length of the inner and outer radial crowns, the location of the nerve ring and cervical papillae, as well as their sizes). In male nematodes of this species, 15 indicators characterize the metric parameters of the reproductive system (the size of the spicules in their various parts, gubernaculum, genital cone, genital papillae and their location, the width of the copulatory bursa). In females, 7 indicators are described that characterize the length of the vagina, the ovipositor, the location of the vulva and anus, the width of the body in the area of the vulva and anus, as well as two metric parameters of eggs. The identified and described morphometric characters of O. venulosum males and females based on microscopic studies can be an economical and effective method for researchers to accurately identify nematodes of this species. The information obtained in this study can contribute to the timely planning of control and prevention strategies for the parasitism of these nematodes on goat farms.

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