# Relationship between oxygenated fatty acid and milk fat concentration during diet-induced milk fat depression in dairy cows

## TL;DR

This study found that specific oxygenated fatty acids in milk fat increase during diet-induced milk fat depression in cows and are linked to other known fatty acid changes.

## Contribution

The study identifies 10-oxostearic and 10-hydroxystearic acids as potential markers for milk fat depression in dairy cows.

## Key findings

- 10-oxostearic and 10-hydroxystearic acids increased in milk fat during diet-induced milk fat depression.
- These oxygenated fatty acids were positively correlated with trans-10 18:1 fatty acid.
- Oxygenated fatty acids may serve as markers for milk fat depression.

## Abstract

Summary: Diet-induced milk fat depression is associated with specific trans fatty acids (FA) intermediates of ruminal biohydrogenation of unsaturated FA. Ruminal metabolism also results in the production of oxy and hydroxy FA. These have not been as well investigated, but we characterized their concentration in milk fat during milk fat depression. Both 10-oxostearic acid and 10-hydroxystearic acid were detectable in milk fat, were increased during diet-induced milk fat depression, and were positively correlated with trans-10 18:1 previously associated with altered biohydrogenation. These oxygenated FA may be used as markers for milk fat depression, and future work should explore whether they have a causative role in the condition. Graphical abstract created in BioRender (https://BioRender.com/s88w866).

Summary: Diet-induced milk fat depression is associated with specific trans fatty acids (FA) intermediates of ruminal biohydrogenation of unsaturated FA. Ruminal metabolism also results in the production of oxy and hydroxy FA. These have not been as well investigated, but we characterized their concentration in milk fat during milk fat depression. Both 10-oxostearic acid and 10-hydroxystearic acid were detectable in milk fat, were increased during diet-induced milk fat depression, and were positively correlated with trans-10 18:1 previously associated with altered biohydrogenation. These oxygenated FA may be used as markers for milk fat depression, and future work should explore whether they have a causative role in the condition. Graphical abstract created in BioRender (https://BioRender.com/s88w866).

•Oxygenated FA were detected in milk fat by gas chromatography-mass spectrometry (GC-MS).•Specific oxygenated FA were increased during diet-induced milk fat depression.•Some oxygenated FA were positively correlated with trans-10 18:1.•Future work is needed to establish possible functional roles of the oxygenated FA.

Oxygenated FA were detected in milk fat by gas chromatography-mass spectrometry (GC-MS).

Specific oxygenated FA were increased during diet-induced milk fat depression.

Some oxygenated FA were positively correlated with trans-10 18:1.

Future work is needed to establish possible functional roles of the oxygenated FA.

Altered rumen biohydrogenation of UFA is central to the current understanding of diet-induced milk fat depression (MFD) in dairy cows, and associations with numerous trans fatty acids (FA) have been characterized. Although some specific CLA isomers have been demonstrated to be antilipogenic, they fail to account for the full decrease in milk fat synthesis during diet-induced MFD, indicating that other undiscovered bioactive causative actors likely exist. Microbial FA metabolism also results in synthesis of oxy and hydroxy FA and the objective of the current study was to quantify changes in these during diet-induced MFD. We hypothesized that 10-oxo-stearic and 10-hydroxy-stearic acid (10-O-18:0 and 10-OH-18:0) would be increased in milk fat during diet-induced MFD. Milk fat samples from 2 experiments that fed diets resulting in MFD were analyzed. In the first experiment (n = 24), diet-induced MFD increased milk fat concentration of 10-O-18:0 from 0.04% to 0.14% of FA and 10-OH-18:0 from 0.07% to 0.21% of FA, whereas milk fat concentration was decreased 43% and milk fat trans-10 18:1 increased from 0.04% to 12.0% of FA. A second experiment that resulted in varying degrees of MFD between the cows was combined to create a dataset for regression analysis (n = 96; trans-10 18:1 ranged from 0.27% to 6.69% of FA). In this dataset, 10-O-18:0 and 10-OH-18:0 were quadratically related to trans-10 18:1 and ratio of trans-10 18:1 to trans-11 18:1 in milk fat but not trans-11 18:1. These results indicate an association of the oxygenated FA 10-O-18:0 and 10-OH-18:0 with diet-induced MFD. Their causative roles in the physiology of MFD warrant further investigation.