# Isolation of Aerobic Bacterial Species Associated with Palpable Udder Defects in Non-Dairy Ewes

## TL;DR

This study found that certain bacteria are linked to udder defects in non-dairy ewes and suggests culling affected animals could reduce future issues.

## Contribution

The study identifies specific bacterial species associated with udder defects and their persistence over time in non-dairy ewes.

## Key findings

- Staphylococcus species, Mannheimia haemolytica, and Streptococcus were most frequently isolated from defective udder halves.
- Bacterial species isolated from defective udder halves showed greater stability over time compared to less frequently isolated species.
- A high agreement (91.5%) was observed between bacterial species identified from milk and mammary tissue swab samples post-weaning.

## Abstract

Milk or mammary tissue swab samples were collected from both defective and normal udder halves in three different studies to identify the bacterial species involved. Samples were collected at different physiological time points: pre-mating, throughout lactation, at weaning and post-weaning. Numerous bacterial species were identified, with Staphylococcus species, Mannheimia haemolytica and Streptococcus being the most frequently isolated. Bacteria were isolated from at least one third (udder lumps) or more than half (hard udder) of defective udder halves, whereas no bacteria were isolated from more than two thirds of normal udder halves. Frequently isolated bacterial species tended to persist longer, whereas less frequently isolated bacterial species showed less stability over time. Bacterial species more frequently identified from defective udder halves and which appear more stable over time should be considered as a factor for making culling decisions.

The objectives of these studies were to identify associations between udder half defects (hard or lump) and bacteria isolated from milk or mammary tissue swabs, to compare with samples from normal udder halves at different physiological time points and to compare bacterial species isolated via milk and swabs of mammary tissue from within the same udder halves. A total of 1054 samples were aseptically collected from each udder half of 199 non-dairy breed (Romney) ewes from three different studies (Study A, n = 77; Study B, n = 74; and Study C, n = 48). Conventional bacterial culture and MALDI-ToF mass spectrometry were used for bacterial identification. Of the 225 samples from which bacteria were isolated, Mannheimia haemolytica and Streptococcus uberis were the dominantly identified species from defective udder halves, whereas coagulase-negative staphylococcus (CNS) species, mostly Staphylococcus simulans and Staphylococcus chromogenes, were more frequently isolated from normal udder halves. The ongoing presence of bacterial species over time was variable, although less frequently identified species showed less stability over time. A very high agreement (91.5%) of bacterial species identified was observed between the mammary tissue swab and udder half milk samples during post-weaning. In summary, palpable udder half defects were associated with bacterial positivity, and the ongoing presence of the bacteria over time was dependent on the species involved. Hence, culling ewes with palpable udder half defects that had more stable bacterial species could contribute to reducing the recurrence of palpable defects or mastitis.