increased ODR and negative effects on health, body weight and reproductive measures Blood pepsinogen concentration, which increases with abomasal mucosa injury has also been used to diagnose ostertagiosis. The analysis of sera for increased plasma pepsinogen levels is a useful diagnostic aid. Generally, increased levels of pepsinogen activity (tyrosine levels >3 IU) are associated with clinical abomasal parasitism. Treatment and control strategies There are several classes of anthelmintic drugs used to control gastrointestinal nematodes in livestock. The most common in the cattle industry are macrocyclic lactones, which include ivermectin and eprinomectin, benzimidazoles, and imidazothiazoles are also used to a lesser extent. Due to routine, blanket herd treatment, there is widespread resistance to anthelmintic drugs in warm climates in sheep, and increasing evidence of resistance in cattle in temperate climates. As a consequence, livestock industries will have to adapt husbandry practices to manage internal parasites. This may include a variety of combinations of pasture rotations, flexible stocking rates, and genetic selection. Several new control methods are also being researched including vaccines, nematode-trapping fungi, and tannins in feed. Drench resistance Given the importance of effective parasite control, there is heightened concern over reduced anthelmintic efficacy. There is a broad range of current literature reporting developing resistance of O. ostertagi to all major classes of anthelmintic worldwide including the United States, New Zealand, Brazil, Argentina, and the UK. As recently as January 2016, O. ostertagi anthelmintic resistance was reported to all three major drug classes on 20 dairy farms in Southern Australia The two most widely accepted anthelmintic resistance diagnosis methods for O. ostertagi are in vivo methods: the fecal egg count reduction test (FECRT) and the controlled efficacy test (CET). The World Association for the Advancement of Veterinary Parasitology (WAAVP) has provided guidelines on the detection of anthelmintic resistance. References Parasitic nematodes of mammals Strongylida