# Reanalysis of 2 metritis studies demonstrates different patterns of postpartum uterine infection for primiparous versus multiparous cows

## TL;DR

The study found that young and older cows handle uterine infections differently, which might explain why young cows get sick more often.

## Contribution

The study reveals distinct bacterial abundance patterns in healthy primiparous and multiparous cows postpartum, offering new insight into metritis resistance.

## Key findings

- Healthy primiparous cows showed a temporary increase in metritis pathogens followed by a decrease.
- Healthy multiparous cows maintained low pathogen levels post-challenge.
- Different infection patterns may explain lower metritis incidence in multiparous cows.

## Abstract

Summary: Metritis typically has a greater incidence in primiparous compared with multiparous cows. To identify biological mechanisms that underlie the observed parity difference in metritis incidence, we reanalyzed the relative abundance of bacterial genera from 2 previous studies that tested a metritis challenge model in primiparous and multiparous cows. We unexpectedly found that primiparous cows that failed to develop metritis (remained healthy) had a different bacterial profile (relative abundance) than multiparous cows that failed to develop metritis following challenge. Specifically, healthy primiparous cows had an initial increase (week 1 postpartum) followed by a decrease (week 2 postpartum) in the relative abundance of metritis pathogens, suggesting the establishment followed by resolution of infection. For healthy multiparous cows, relative abundance remained low following the challenge. In this reanalysis of 2 independent studies, we found different patterns of infection for primiparous compared with multiparous cows.

Summary: Metritis typically has a greater incidence in primiparous compared with multiparous cows. To identify biological mechanisms that underlie the observed parity difference in metritis incidence, we reanalyzed the relative abundance of bacterial genera from 2 previous studies that tested a metritis challenge model in primiparous and multiparous cows. We unexpectedly found that primiparous cows that failed to develop metritis (remained healthy) had a different bacterial profile (relative abundance) than multiparous cows that failed to develop metritis following challenge. Specifically, healthy primiparous cows had an initial increase (week 1 postpartum) followed by a decrease (week 2 postpartum) in the relative abundance of metritis pathogens, suggesting the establishment followed by resolution of infection. For healthy multiparous cows, relative abundance remained low following the challenge. In this reanalysis of 2 independent studies, we found different patterns of infection for primiparous compared with multiparous cows.

•Cows had an increase in metritis-causing pathogens during the first 2 weeks postpartum.•Primiparous cows that remained healthy had increased metritis-causing pathogens in week 1.•Multiparous cows that remained healthy had a different pattern than primiparous cows.•We found different patterns of infection for primiparous compared with multiparous cows.

Cows had an increase in metritis-causing pathogens during the first 2 weeks postpartum.

Primiparous cows that remained healthy had increased metritis-causing pathogens in week 1.

Multiparous cows that remained healthy had a different pattern than primiparous cows.

We found different patterns of infection for primiparous compared with multiparous cows.

Metritis typically has a greater incidence in primiparous compared with multiparous cows. In separate studies with similar design, we noted that primiparous and multiparous cows responded differently to a model developed to induce metritis via the intrauterine infusion of a bacterial challenge of Fusobacterium necrophorum, Trueperella pyogenes, and Escherichia coli. To understand the difference between primiparous and multiparous cows, we reanalyzed the relative abundance of bacteria genera within the vaginal microbiome during the first 2 wk postpartum from the 2 previous studies for primiparous and multiparous cows. We conducted a first reanalysis of primiparous and multiparous cows that received an identical challenge dose (106 cfu of each pathogen) and a second reanalysis that compared all primiparous and multiparous cows that were or were not diagnosed with metritis regardless of challenge dose (0, 103, 106, or 109 cfu per pathogen). The challenge model resulted in clinical metritis in both primiparous and multiparous cows, although some control cows (0 dose) developed metritis and, conversely, some bacterial challenge cows failed to develop metritis. Importantly, cows that contracted metritis had increased and sustained relative abundance of key metritis pathogens including Fusobacterium, Porphyromonas, Helcococcus, and Trueperella after calving regardless of parity. We unexpectedly found, however, that primiparous cows that did not develop metritis had a different bacterial profile (based on 16S ribosomal gene sequencing as well as bacterial culture) compared with multiparous cows that did not develop metritis. In primiparous nonmetritis cows, the relative abundance of the genera Fusobacterium, Porphyromonas, Helcococcus, and Trueperella was almost identical to primiparous metritis cows during the first week postpartum, but the relative abundances in nonmetritis cows decreased rapidly thereafter. The relative abundance of the same genera in nonmetritis multiparous cows did not increase or increased to a lesser extent postpartum. The different patterns of infection for nonmetritis primiparous (initial increase in relative abundance [wk 1] followed by a decrease [wk 2]) compared with nonmetritis multiparous cows (stable and low-level relative abundance for 2 wk postpartum) was found when the analysis included only challenge cows (106 cfu dose) or all cows regardless of dose. We found different patterns of infection for primiparous compared with multiparous cows. This observation may explain lesser incidence of metritis in multiparous compared with primiparous cows.