# Negative Energy Balance in Transition Cows Induces Complex Changes in Lipid Profile of Milk

## TL;DR

This study shows that negative energy balance in dairy cows during the transition period causes complex changes in milk lipid profiles, identifying potential biomarkers for energy status.

## Contribution

The study identifies nine specific lipids as potential biomarkers for negative energy balance in dairy cows.

## Key findings

- NEB caused significant modifications in multiple milk lipid classes, including phospholipids and triglycerides.
- Lipids like PE 33:1 and several LacCer and SM species were identified as potential biomarkers for NEB.
- Species with de novo and odd-chain fatty acids were downregulated, while those with long-chain preformed fatty acids were upregulated.

## Abstract

Background: Negative energy balance (NEB) during the transition period is associated with profound changes in the body condition and metabolic dynamics of dairy cows. However, the detailed lipidomic changes in milk induced by NEB are unclear, and lipid biomarkers that indicate the energy status of cows remain to be established. Methods: Using a combination of GC-FID, HILIC-MS and RP-LC-MS, we performed a systematic comparison of lipid composition between early lactating (DIM: 5–14) and mid-lactating (DIM: 65–80) milk. Results: We found that NEB in cows caused a profound modification in the profile of all the lipid classes surveyed, including phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), sphingomyelin (SM), lysophosphatidylcholine (LPC), PC-plasmalogen (PCP), PE-plasmalogen (PEP), lactosylceramide (LacCer), acylcarnitine (AcylCar) and triglycerides (TAGs). Except for LPC and AcylCar, which were reduced and increased, respectively, by NEB, the responses of other lipid classes varied across different species. For phospholipids and TAGs, species containing de novo FAs (C4:0–C16:0) and odd-chain FAs (C15:0 and C17:0) were markedly downregulated, whereas those comprising long-chain preformed FAs were upregulated by NEB. Conclusions: Comprehensive lipidomic profiling of early and mid-lactating milk from two large cohorts of cows allowed us to identify nine lipids (PE 33:1, LacCer 32:1, LacCer 39:1, LacCer 41:1, SM 36:1, SM 36:2, SM 37:1, PEP 38:4 and PEP 38:5) as potential biomarkers of NEB in dairy cows.