Identifying the Rumen Bacteria that Improve Beef Production and Carcass Quality

Background

The past decade of research has shown that bile acids can play a key role in influencing an animal’s body which can result in positive health effects. This includes changing the composition of the microbiome in the digestive system and stimulating the immune system.  In the case of cattle, this could have the potential to influence carcass quality.

Specifically, cholic acid, a bile acid produced in the liver from cholesterol, while not toxic itself, it causes gut bacteria to transform into toxic metabolites like deoxy- and lithocholic acid. This is not a unique phenomenon with gut bacteria producing many secondary bile acids which have modified steroid rings which have toxic and other unknown activities. Other cholic acid metabolites can be used as biomarkers like 3-oxo-4,6-choladienoic acids which vary slightly in structures but can have a positive or negative impact on average daily gain in cattle. Additionally, ursodeoxycholic acid which was found to increase meat quality and marbling without effecting dressing percent, fat thickness or rib eye area.

However, there’s still a lot we don’t understand about these bile acid-related substances and how they affect the quality of beef. Identifying and understanding more about these substances and how they relate to the quality of meat could fill an important gap in our knowledge about animal health and meat quality.

Objectives

• Catalogue secondary bile acids in beef cattle
• Identify bacteria and bacterial enzymes involved in their production

What they Did

A series of fecal samples from operations in Alberta, Saskatchewan and Ontario were utilized to survey the bile salts and acids present in beef cattle using high-resolution mass spectrometry. In parallel, bacterial isolation and cultivation was performed to begin to identify sources of bile acid modifications and the underappreciated changes to the metabolite pool. This collection of isolates can be used to better characterize the secondary bile acids that are not reliably identified by generalized mass spectrometry workflows but that may impact animal health and beef quality.

What They Learned

The targeted investigation of the bile acid pool and bacterial cultivation of fecal samples showed similar metabolites and bacterial metabolic capacities across samples despite differences in geography and feedlot management. This team was able to isolate bacteria of the genus Arthrobacter readily from samples of varying origins and found they collectively had a capacity to produce at least 10 long-lived metabolites from DCA in vitro. The results of the metabolomic survey also revealed a series of molecules that were consistently present in cattle fecal samples but that could not be definitively identified. Therefore, there is a need to generate, isolate and characterize these secondary bile acids to understand their impacts on beef performance and quality. Given the data yielded from the study, it can be speculated that bacterial transformation products may arise from the action of Arthrobacter spp. and/or other bacteria.

Finally, in one application of the high-resolution mass spectrometry (HRMS) methodology, revealed an increased amount of total fecal bile acids was correlated to the addition of water to a finishing diet. There were a handful of metabolites that were differentially abundant between the two groups (added water to feed and not), but these could not be identified using conventional bile acid-targeted HRMS analysis alone. The group which had water added to their feed were found to have more consistent marbling scores than controls but were also at a higher risk of acidosis. Definitively identifying the specific metabolites contributing and their varying abundancies could help to understand why this result was observed. 

What This Means

Fecal metabolomics platforms are poised to offer a non-invasive sampling tool, however, there are major gaps in our knowledge of the beef cattle bile salt and acid pool in terms of content and how it influences health and carcass quality. More extensive and integrated research between microbiologists, biochemists, chemists and nutritional physiologists is required to understand the molecular and production impacts of the secondary bile acid pool. This will be essential in order to rely on these metabolites as biomarkers and could lay the groundwork to  develop a dietary supplement that can manipulate the pool of these metabolites that influences cattle performance.