Summary
This controlled field trial in three rumen-cannulated Angus steers examined how increasing dietary narasin (13, 20, or 27 ppm) modified ruminal function, microbial ecology, and nutrient utilisation in feedlot diets. Narasin supplementation improved ruminal pH stability and altered short-chain fatty acid production in a dose-dependent manner, with lower doses (13 ppm) enhancing acetate and propionate production, whilst higher doses (27 ppm) reduced ammonia and total SCFA. The additive increased ruminal abundance of Lachnospiraceae and Isotricha whilst reducing lactic acid–producing bacteria, and at 20 ppm increased ruminal papillae keratin layer thickness, suggesting benefits for epithelial integrity.
Regional applicability
This study was conducted in Brazil and examined narasin, an ionophore coccidiostat licensed for use in cattle in some jurisdictions. In the United Kingdom, regulatory context for ionophore use in cattle feedlots differs; the findings on ruminal pH stability and microbial modulation may inform understanding of ionophore mechanisms but direct applicability to UK feedlot practice requires verification of current narasin regulatory status and typical UK feedlot management systems.
Key measures
Ruminal degradability, apparent digestibility (ADF, dry matter), continuous ruminal pH, short-chain fatty acids (acetate, propionate, butyrate), ammonia concentration, lactate concentration, acetate-to-propionate ratio, ruminal microbial composition (16S rRNA or metagenomics), ruminal papillae histology (keratin layer thickness)
Outcomes reported
The study measured ruminal fermentation patterns (SCFA, ammonia, lactate), bacterial community composition, nutrient digestibility (ADF, dry matter), ruminal pH stability, and papillae histology in response to three narasin dosages (13, 20, 27 ppm). Narasin supplementation modulated ruminal microbial ecology and fermentation efficiency, with dose-dependent effects on pH stability and microbial abundance.
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