PSI-19 Plasma haptoglobin concentration as a potential biomarker for stress caused by horn fly infestation in lactating beef cows.

Abstract The horn fly parasite has a negative impact on cattle because of its irritating and painful bites, which can reduce animal performance and welfare due to the resultant stress. This experiment aimed to evaluate the relationship between plasma haptoglobin (Hp) concentrations and horn fly load in lactating Angus crossbred beef cows under various parasite control treatments. A two-year study was conducted from May to October in 2023 and 2024. Each year, 48 multiparous Angus crossbreed cow-calf pairs were utilized. The experiment followed a randomized complete block design with four treatments in a 2 × 2 factorial arrangement. Factors included the use or not of internal (INT) or external (EXT) parasite control. Animals were sorted by age and weight and randomly grouped into four cow-calf pairs assigned to 12 different pastures (n = 4 cow-calf pairs/pen, 3 pens/treatment each year). On the day the animals were sorted into treatments (d 0), they received the first dose of parasite control. Endoparasite control involved administering a drench containing 11.36% albendazole (45 mL and 15 mL for cows and calves, respectively). For ectoparasite control, animals were equipped with ear tags coated with 50% organophosphate insecticides (2 ear tags per cow and 1 per calf) and treated with a pour-on application of 1% permethrin synergized with 1% piperonyl butoxide. On the first day of the experiment, the INT treatment was reinforced with the same initial dose, and the pour-on was re-applied on every sampling day thereafter. On d 1, 35, 70 (weaning day), and 105, body weight (BW) and body condition score (BCS) were recorded, and photographs of the cows’ right-lateral side were taken to determine horn fly load. Additionally on each sampling day, blood samples were collected by jugular venipuncture to determine plasma Hp concentrations. No effect of INT, or EXT × INT interaction was observed (P > 0.05) on number of flies per cow. However, a main effect of EXT was observed on horn fly infestation (P < 0.05) where the external parasite control reduced fly counts by 28.6%. Flies counts exerted a positive strong effect on Hp concentrations in plasma (P < 0.01), and external parasite control tended to affect Hp concentrations (P = 0.06). There was no INT or EXT × INT interaction (P > 0.05) for plasma Hp concentrations. Haptoglobin concentrations in plasma were not influenced (P > 0.05) by the BW of the cow or the calf nor by the BCS of the cow. External parasite control reduces horn fly load, which significantly impacts Hp concentrations in plasma. Further studies should be conducted to evaluate the potential of Hp as a biomarker for ectoparasitic burden in cattle systems.