Fact Sheet: Yeast and Prototheca

Yeast infections

Yeasts or there spores are very common in the dairy environment. Most animals show a high degree of resistance to infection by yeasts. A yeast infection suggests a major breach in the cows defense mechanisms. A common way for yeast to enter the udder is by infusion of contaminated treatment preparations or using contaminated infusion equipment. This bypasses the cows first line of defense at the teat-end. Milking machine malfunction or poor milking technique may also allow entry of yeast organisms into the udder. Yeasts do not respond to antibiotics and the use of antibiotics may worsen the signs of mastitis Most cases of yeast infection will resolve with in two months with out treatment. Individual cases of yeast mastitis are not a herd problem but suggest a look at certain management practices.


  • Whether dry cow or lactating cow treatment use a new, single use udder preparation only.

  • Clean teat-end and hands prior to infusion. The use of sterile gloves is recommended.

  • Avoid the use of bulk mastitis treatments. A contaminated bulk supply could infect a large number of cows.

  • Ensure sterility of all infusion equipment, teat tubes, dilators, etc. and only use them after carefully cleaning the teat-end. It is best to avoid the use of this type of equipment altogether.

  • Be sure the milking equipment is working properly.

  • Be sure all milkers are using good technique and proper hygiene.

Prototheca infections

Prototheca is an algae and as such has an affinity for water. It is found in soil, plants, streams, ponds, manure and wet areas of barns and holding areas. Prototheca enters the udder just as Nocardia, with passage of an infusion device through an inadequately sanitized teat-end. An infected cow can shed the algae at milking and so should be milked last or with separate equipment. The mastitis caused by prototheca can be acute or subclinical and chronic. Infection with prototheca does not respond to antibiotics and culling is the treatment of choice. Good infusion technique and a dry environment are preventative.