# Pilot Study: Soluble LPS/IgG Milk Complexes in Relationship to Early Lactation Acute Mastitis in Dairy Cows

## TL;DR

This study explores how LPS/IgG complexes in cow milk relate to the severity of mastitis caused by Gram-negative bacteria in early lactation.

## Contribution

The study introduces milk-soluble LPS/IgG complexes as a potential biomarker for detecting and managing acute mastitis in dairy cows.

## Key findings

- Higher sLPS/IgG levels were found in cows with acute mastitis caused by Gram-negative bacteria.
- Milk sLPS/IgG absorbance profiles varied based on the type of bacterial infection.
- The presence of sLPS/IgG complexes correlates with mastitis severity in early lactation.

## Abstract

Acute udder inflammation (mastitis) often occurs in cows early in the lactation cycle. Mastitis is primarily caused by a wide range of bacteria including both Gram-negative and Gram-positive species. Gram-negative infections frequently result in severe mastitis due to the presence of pro-inflammatory compounds known as lipopolysaccharides (LPS). During the immune response, removal of LPS involves antibodies in the udder that form immune complexes, which support the clearance of bacteria and toxins from the udder and help the cow return to good health and milk production. This study identifies soluble LPS/IgG immune complexes in milk and explores the notion that milk-soluble (s) LPS/IgG complex levels in dairy cows link mastitis severity to intramammary Gram-negative infections during early lactation. We measured soluble milk LPS/IgG complexes alongside a known marker of udder inflammation (lactate dehydrogenase activity) in healthy cows and cows with subclinical or acute mastitis. Our results showed that increased milk levels of soluble LPS/IgG complexes were associated with acute udder inflammation caused by Gram-negative bacterial infections. This suggests measuring milk-soluble LPS/IgG complexes could be useful in the detection and management of acute mastitis in dairy cows.

Prevalence of LPS in Gram-negative bacterial udder infections determines mastitis severity and disease prognosis. This pilot study explores the notion that milk-soluble (s) LPS/IgG complex levels in dairy cows link mastitis severity to intramammary Gram-negative infections during early lactation. Milk, within a single herd, was analysed from (i) 34 early lactating cows with acute mastitis and (ii) milk selected from peak lactation cows displaying either healthy (SCC < 100 × 103 cells/mL, n = 146) or subclinical mastitis (SCC > 150 × 103 cells/mL, n = 135) characteristics. Milk was assessed for (i) sLPS/IgG using an “in-house” ELISA, (ii) udder inflammation using LDH activity, and (iii) bacterial presence applying on-farm and standard microbiological laboratory techniques. Mean milk sLPS/IgG absorbances in acute mastitis cows were higher than those detected in healthy and subclinical mastitis cows, with mean differences of 0.35 (95% CI, 0.28 to 0.42) and 0.36 (95% CI, 0.28 to 0.44), respectively. On day 1 of acute mastitis, sLPS/IgG levels in milk containing only Gram-positive bacteria ranged from OD 0.04 to 0.14 (median = 0.1). In contrast, sLPS/IgG levels ranging from OD 0.27 to 1.42 (median = 0.58) and from 0.02 to 1.67 (median = 0.21) were detected in milk containing only Gram-negative bacteria or both Gram-negative and Gram-positive bacteria (i.e., polymicrobial), respectively. Furthermore, differential milk sLPS/IgG absorbance profiles (observed during the testing period days 1–3) were observed in cows with acute mastitis caused by Gram-positive, Gram-negative or polymicrobial infections. Our preliminary findings support the notion that milk sLPS/IgG complexes provide a link between mastitis severity and intramammary Gram-negative infections in dairy cows during early lactation.