Introduction
Prototheca spp. are colorless, achlorophyllous, unicellular algae that thrive in dairy environments and are responsible for clinical and subclinical, non-responsive mastitis, especially during warmer months. Studies have shown that Prototheca are capable of establishing biofilms. Other studies have shown that chlorine dioxide is effective in penetrating and disrupting biofilm slime layers. Fecal shedding from dairy cattle and biofilm formation make eradicating Prototheca difficult in holding areas, exit alleys, walkways, and flush water systems of modern dairies.
During spring and summer 2022, a privately owned commercial dairy in upstate New York suspected the milking parlor flush water, holding area, and exit alley as risk factors contributing to seventy-three Prototheca mastitis cases. From February–September 2023 the flush water tank, and grooved concrete surfaces of the holding area and exit alley were treated with chlorine dioxide 100 parts per million (ppm) to break down Prototheca biofilms thereby diminishing the presence of Prototheca and lessen the risk of Prototheca mastitis.
Materials and Methods
The project farm milks approximately 3200 Holstein dairy cows three times daily on a 72 stall rotary parlor. All fresh water used to hose down the parlor and to wash the milking system is collected into a 3,000 gallon holding tank. After each milking group the parlor entrance and exit is flushed with holding tank flush water. The flush system is activated to remove manure from the holding area and exit alley at the end of each milking group. Although no animals are in the direct vicinity of the flush water valves when triggered, cows are held in these areas with flush water potentially splashing up and contaminating teats and udders. Chlorine dioxide was applied to disrupt biofilms in the flush water holding tank and to remove existing biofilms in the holding area and exit alley.
The flush water tank was initially shocked in February 2023 with 379 L (100 gal) of chlorine dioxide (500 ppm) through the milk house floor drain flowing directly into the holding tank. Maintenance doses of 19 L (5 gal) of chlorine dioxide (500 ppm) began in August 2023.
A chlorine dioxide two-zone spray system was installed on a suspended bar across the entrance and exit to the milking parlor. The system consists of a 1041 L (275 gal) IBC tote, pump, and seven spray nozzles across the entrance (zone 1) and three spray nozzles across the parlor exit (zone 2). The spray system was activated for 30 seconds with a 30 second delay after the initiation of the flush water system. Nozzle size and spray duration dispersed 2.1 L (0.5 gal) of chlorine dioxide (100 ppm) in zone 1 and 0.89 L (0.24 gal) in zone 2.
Results and Discussion
Prototheca was detected in 80% of the flush water samples collected before shocking and 14% after shocking. Prior to implementing the chlorine dioxide spray system, a slime layer was observed in less trafficked areas of the holding area and exit alley with Prototheca present in 61% of the samples. Slime layer dissipation was observed after one month with 60% of the swab samples Prototheca positive after applying chlorine dioxide.
Flush water tank shocking showed immediate reduction in Prototheca lasting five months. During March–July confirmed Prototheca mastitis cases dropped from 50 in 2022 to 14 cases in 2023. Prototheca was detected in all samples collected in late July 2023 with 19 mastitis cases occurring in August 2023. Introduction of weekly shocking of the flush water tank eliminated Prototheca from the flush water with mastitis declining to 5 cases in September 2023 (14 cases noted in September 2022).
Conclusion
Chlorine dioxide is proven to disrupt established algae-based biofilms and reduce their presence in water holding tanks and the environment. As a major non-responsive environmental and contagious mastitis pathogen, Prototheca is capable of producing biofilms believed to perpetuate intramammary infections on modern dairy farms. Ideally, proper risk reduction of Prototheca mastitis should include individual animal cultures and appropriate management to prevent contagious spread by positive animals and treatment of the environment to reduce Prototheca presence and its potential for environmental mastitis.
Developing innovative, eco-friendly, and cost effective application methods of disinfectants such as chlorine dioxide, along with traditional dairy environment management practices, is essential to reduce future environmental mastitis cases from Prototheca and other environmental pathogens.