Udder sores are those nasty skin lesions seen in front of the udder or between the udder cleft. The lesions are difficult to heal, and unlucky cows can even bleed to death if the lesion punctures the udder vein in very severe cases.
Mostly cows with larger udders seem to be affected by those lesions. While some farms see lots of them, others rarely see those lesions. There have been many different theories about what causes them: mange, fungi, the same bacteria as digital dermatitis (spirochetes) or even viral infections (herpes virus).
To find out if those theories were true and which pathogens were actually present in those lesions, researchers from the University of Minnesota visited three different farms in Minnesota. Two of the participating farms were high-producing herds with over 400 milking Holstein cows housed in freestalls with either sand-bedded freestalls or sawdust-covered mattresses.
The other farm had about 250 milking cows (mixed breeds) on pasture. Both high-producing herds had over 50% of cows with udder sores of various degrees of severity, while the smaller farm had less than 10% of cows with mild or healed udder sore lesions.
On each farm, the researchers took skin biopsies of the lesions of several affected cows (23 lesion samples in total). As comparison, they also took skin biopsies of healthy skin of those cows as well as of 12 cows without udder sores. The biopsies were evaluated under the microscope by a board-certified pathologist and also at the University of Iowa with an advanced laboratory diagnostic technique (16S metagenomics) to describe the bacterial skin and lesion flora in detail.
Interestingly, the findings across all three farms were fairly consistent – although the skin flora of cows differed slightly among farms. No signs of mange, viral or fungal infections were detected in any of the samples under the microscope. Therefore, those suspects are unlikely causes of udder sores. Furthermore, spirochetes, the causal pathogen of digital dermatitis, were found in healthy and lesion skin biopsies on all three farms.
However, their relative contribution to the skin and lesion flora was extremely low and comparable between healthy and damaged skin. Since spirochetes clearly dominate the bacterial flora of digital dermatitis lesions, the findings of this study make them unlikely culprits for udder sores.
Instead, the microbial fractions of various types of bacteria (Fusobacteria, Helcococcus ssp., Anaerococcus ssp., Porphyromonas ssp., Prevotella ssp. and Trueperella ssp.) increased severalfold in lesions compared to control samples. This is a clear shift toward bacteria that have been associated alone or in combination with the other bacteria with other diseases, such as biofilm-building gingivitis or uterine diseases and abscesses in cattle.
Since the bacteria of this mixed infection thrive under low oxygen conditions (anaerobic) and moist “dead spaces” in tight skin folds, they should be watched closely and ideally prevented (i.e., edema prevention, udder conformation). Better understanding of the pathogens associated with these lesions will help develop effective prevention and treatment options for this disease in the future.
A good way to safely screen for lesions and to detect them early is the use of a handheld mirror in front of the udder while the cow is going through the milking parlor. Udder halves of very full or big udders might need to be manually pulled apart or a light source attached to the mirror might be useful in dimly lit parlors to catch the lesions early on, but otherwise the lesions are fairly easily spotted in most cows. Once detected, the lesions could be cleaned and monitored to avoid serious issues.
