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Targeting Inflammation In Heat-Stressed Wethers Improves Growth And Efficiency And Alters Body Composition; A Brief Exploration And Application Of Extension Principles, Micah Most

Department of Animal Science: Dissertations, Theses, and Student Research

The objective of our first study was to determine how administering anti-inflammatory dexamethasone and ω-3 polyunsaturated fatty acid (PUFA)-rich fish oil affects growth efficiency and body composition in heat-stressed finishing lambs. Commercial wethers were randomly assigned to be fed under heat stress (35°-40℃) or thermoneutral (19℃, n = 10) conditions for 30 d, and controls were pair-fed to eliminate differential feed intake. Heat-stressed wethers were randomly assigned to receive clinical-dose dexamethasone IM injections every 72 h, twice daily fish oil capsule oral boluses, or placebos. Heat stress decreased (P < 0.05) growth and efficiency, but dexamethasone and fish oil supplementation recovered these performance measures. Heat stress also decreased (P < 0.05) predictive body composition metrics that were at least partially improved by administration of dexamethasone and fish oil. Proximate analyses of muscles showed that heat stress decreased (P < 0.05) percentage of protein and increased (P < 0.05) percentage of intramuscular fat, neither of which was improved by dexamethasone or fish oil. Immunohistochemistry revealed that heat stress decreased (P < 0.05) myoblast differentiation and muscle fiber size, but anti-inflammatory supplementation recovered differentiation only. Plasma IGF-1 concentrations were not different among groups throughout the study. These findings demonstrate how heat stress-induced inflammation contributes to impaired growth, efficiency, and body composition observed in heat-stressed feeder lambs. However, targeting inflammation with dexamethasone or fish oil recovers many of these deficits.

The Cooperative Extension Service, …