The animal article of the month for June is ‘Invited review: Nutrient sensing receptors for free fatty acids and hydroxycarboxylic acids in farm animals‘.  Author: M. Mielenz

Nutrient sensing by free fatty acid receptors and hydroxycarboxylic acid receptors links energy substrate supply with cellular responses. Both receptor families help the organism to respond to nutrient availability. This response is independent of the function of nutrients as energy substrates, such as for example short-chain fatty acids derived from microbial fermentation. Receptors of both families are found within the intestine, where they represent an interface between fermentation products of the microbial community and the host. However, members of both receptors families are found in a number of other tissues or cells of the organism. Those include adipose tissue or cells of the innate immune system, such as neutrophil granulocytes. Receptors are specifically activated by various free fatty acids or other compounds like beta-hydroxybutyric acid or lactate. Activation of a certain receptor is associated, e.g., with in insulin secretion, regulation of lipolysis or immune response.


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Most data on free fatty acid or hydroxycarboxylic acid receptors are coming from humans or rodent models. In farm animal species, data is often linked with gene expression. Information on the functional importance of free fatty acid receptors in farm animals are currently mostly related to bovine neutrophil granulocytes. The importance of these receptors should be at least partly comparable between humans, rodent models, and farm animals. However, species specific differences in metabolism, like the dominance of short-chain fatty acids for energy supply in ruminants in association with their relatively high concentrations in plasma compared with humans, might be linked with differential abundances between species or different affinities for their ligands. The latter was observed for the bovine receptor FFAR2, specific for short-chain fatty acids.


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In humans, both receptors families are discussed as targets to treat metabolic and inflammatory disorders. The interaction of the microbiota and its host are of significant research interest in humans and farm animals. The composition of the microbiota and its impact on the regulation of metabolism and health is in the current research focus in humans but also in farm animals. Therefore, research on microbiota-host interaction in farm animals may boost also research on both receptor families in farm animals in future.

This article is freely available for one month:

Invited review: Nutrient sensing receptors for free fatty acids and hydroxycarboxylic acids in farm animals‘.

Author: M. Mielenz

The animal Article of the Month is selected by the Editor-in-Chief and is freely available for one month. View the recent selections



  1. Does anyone know if ruminants sense ammonia? Silly question, since ammonia is the most toxic metabolite of any and peripheral concentrations must be sensed to then keep the concentration within safe levels. But the portal vein is different: ammonia levels are higher and not so tightly regulated. Sensing ammonia concentration here so as to downregulate intake when necessary would be sensible, but does it happen?

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