June 25, 2020

Interpretive Summary: Ruminal microbes of adult sheep do not degrade extracellular l-citrulline

Interpretive Summary: Ruminal microbes of adult sheep do not degrade extracellular l-citrulline

By: Anne Wallace

Amino acid (AA) supplementation supports the health, growth and development of livestock animals. Supplementation however can be more challenging in rumen animals because rumen bacteria extensively degrade many amino acids when they are consumed through feeding.

Highly degraded AA are more poorly bioavailable as they do not reach the small bowel intact. If such AA are supplemented in the diet, they may need to be provided in a rumen-protected form to bypass rumen bacteria and preserve bioavailability. Therefore, knowing which AAs are degraded by rumen bacteria can be extremely helpful in maximizing both profit and production.

Researchers in this June 2020 Journal of Animal Science study evaluated whether L-Citrulline would be degraded by rumen bacteria in sheep. An in vitro study was set up using ruminal fluid from adult Suffolk sheep. Four amino acids, L-Arginine (Arg), L-Citrulline (Cit), L-glutamine (Gln), and L-glutamate (Glu) were mixed with the collected ruminal fluid and analyzed. Additionally, in a second simultaneous study, sheep were fed Cit, Gln and urea, and their blood levels were subsequently tested for Cit and Arg. 

Results indicated that Arg and Gln were extensively degraded by rumen bacteria, but Cit and Glu were not. Additionally, sheep fed Cit but not Gln or urea, had increased blood levels of both Cit and Arg. These findings are significant, suggesting that Cit is not only poorly degraded by rumen bacteria, but bioavailable and therefore convertible to the AA Arg, which is degraded by rumen bacteria. Further studies looking at L-Citrulline in other rumen animals may be warranted.