Effectiveness of Anthelmintic Classes in Beef Calves and their Implications on Beef Cattle Performance

Document Type


Degree Name

Master of Science (MS)


Ag Science and Natural Resources

Date of Award

Summer 2020


Damage caused by helminth infection creates a significant loss in profit and production for those managing grazing livestock (Sutherland and Leathwick, 2011). Though all types of helminths can be found in cattle, gastrointestinal nematodes are considered the most economically and physically damaging in the cattle industry. Some of the most common nematodes found in cattle are Haemonchus (stomach worm), Trichostrongylus (hair worm), Ostertagia (stomach worm) and Cooperia (intestinal worm). External parasites are also a large contributor to economic loss in cattle, mainly Haematobia irritans (Horn fly). Parasite populations in cattle are controlled by three classes of anthelmintics (dewormer); macrocyclic lactone (ML), benzimidazoles (BZ), and tetrahydropyrimidines (T/I). However, after years of misuse and continual repeated use of these anthelmintics, reports of parasitic resistance in cattle are now occurring, leaving some producers to have to use a combination of dewormers to combat the nematode populations (Geary et al., 2012). Anthelmintic resistance was determined on the Texas A&M University-Commerce (TAMUC) weaned calves in the fall of 2019 (n = 79) and spring 2020 (n = 35) by conducting Fecal Egg Counts (FEC) and Fecal Egg Count Reduction Test (FECRT) on day 0 and weeks 2 and 6. To determine if a combination deworming method would be more effective compared to standard farm practice (single dewormer). Cattle during the fall trial were assigned to one of four treatment groups; ML pour-on (Cydectin®; n = 21; 1 ml/ 9.98 kg per body weight), BZ drench (Valbazen®; n = 21; 4 ml/ 45.36 kg per body weight), combination of both the pour-on and drench (n = 20), and a control (n = 17). Resistance and comparisons of anthelmintics effectiveness was repeated in the spring of 2020. However, an injectable ML anthelmintic replaced the combination treatment group and pour-on. Calves were assigned to three treatment groups; BZ drench (Valbazen®; n = 12; 4 ml/ 45.36 kg per body weight), ML injectable (Dectomax®; n = 12; 1 ml/ 49.9 kg per body weight), and a control


Douglas Eborn

Subject Categories

Agriculture | Animal Sciences | Life Sciences