Disease & heat resistance

Acute-phase response to horn fly infestation in Bos indicus beef cattle

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Abstract

Economic losses due to horn flies (Haematobia irritans irritans L.) infestations are estimated to exceed $1 billion annually in North America. These hematophagous ectoparasites, which rely almost exclusively on cattle as their primary host, cause discomfort and defensive behaviors such as head throws and tail twitching. Such stress may trigger an acute-phase response, a rapid systemic reaction of the innate immune system characterized by elevated concentrations of acute-phase proteins, including haptoglobin. In cattle, haptoglobin is considered a major APP and is widely used as a biomarker of inflammation, health status, welfare, and physiological stress. However, its response to horn fly infestation under controlled conditions remains poorly understood. Thus, the objective of this study was to investigate plasma haptoglobin as an indicator of physiological stress in cattle and its association with horn fly infestation. A total of 197 purebred Brahman calves, born in 2024 and raised under uniform management, environmental, and nutritional conditions at the University of Florida Beef Research Unit, were evaluated at weaning. For each calf, dorsal images were captured, followed immediately by blood collection. Animals were clinically healthy at the time of sampling, and horn fly counts were determined as the average number of flies across three images per animal using ImageJ software. Based on the distribution of fly counts in the population, 72 calves (36 males and 36 females) were selected for plasma haptoglobin analysis and classified into Low and High infestation groups, each containing 18 males and 18 females. The Low infestation group showed a mean fly count of 5.94 ± 6.57, ranging from 0 to 18 flies, whereas the High infestation group had a mean fly count of 139 ± 92.13, ranging from 53 to 368 flies per animal. Plasma haptoglobin concentrations were quantified using a commercial ELISA kit (bovine haptoglobin, E-10HPT, Immunology Consultants Laboratory, Portland, Oregon, USA) and calculated using a four-parameter log-logistic standard curve (R²=0.9998; slope=1.10±0.03). Data were analyzed using a linear model, and plasma haptoglobin concentrations were log-transformed to stabilize variance and improve normality of the residuals. Plasma haptoglobin concentration and age at weaning were significantly associated with horn fly count (P < 0.01). Horn fly infestation induced measurable physiological responses, with plasma haptoglobin increasing in relation to fly infestation and age. While most haptoglobin values remained within ranges typically associated with the absence of clinical inflammation, the numerical trend in high infested animals highlights a potential biological response to horn fly infestation. Incorporating additional acute-phase proteins or stress-related biomarkers may provide a more comprehensive understanding of cattle responses and variation in resilience to horn fly challenge.

Keywords: 2026

How to Cite:

Baker, O., Burgess, E., C. Ladeira, G., Galandauer, M., Rasia, J., Rezende, F. & Tayama, P., (2026) “Acute-phase response to horn fly infestation in Bos indicus beef cattle”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2286779. doi: https://doi.org/10.31274/wcgalp.24119

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