Effects of Catecholamines on Gut Microflora and Potential for Beta- Adrenergic Agonists to Impact Ruminal Fermentation

Abstract

Catecholamines are produced by chromaffin cells of the adrenal medulla and adrenergic and dopaminergic neurons from tyrosine. Catecholamines regulate many vital physiological and metabolic responses because of the location of receptors. The impact of catecholamines is not limited to mammals; direct effects of natural catecholamines on bacteria have been researched extensively to understand the potential impact of these compounds on bacterial infections in humans. Catecholamines have increased the growth of bacteria, virulence-associated factors, and adhesins and increased biofilm formation. Beta-adrenergic agonists are similar in structure and pharmacological properties to natural catecholamines. Beta-adrenergic agonists enhance performance of finishing cattle during the final days prior to harvest. Responses to beta-adrenergic agonists include increased average daily gain, improved feed efficiency, and increased carcass lean. These responses have been observed as a direct effect to the animal; however, a review of the literature suggests that the response to beta-adrenergic agonists also could be mediated by a direct or indirect effect on ruminal microorganisms. Ractopamine hydrochloride increased fermentation in vitro, particularly with increased amounts of degradable intake protein. Inclusion of ractopamine hydrochloride in vivo decreased ruminal concentrations of ammonia and amino acid. The rumen is host to a large population of diverse microorganisms, and a direct impact of a synthetic catecholamine on the microbial population could potentially alter fermentation and the ruminant performance. Reviewing literature on catecholamines and their direct impact on microorganisms could lead to improved decisions regarding dietary supplementation of beta-adrenergic agonists, threreby increasing the growth performance response in ruminants.