In pre-harvest poultry production, live Salmonella vaccines are often administered through drinking water, thereby requiring water quality to be compatible with live vaccines. A new in vitro study has identified drinking water qualities and contaminants that can affect the viability of an available Salmonella vaccine for poultry.

The research evaluated how water pH, hardness, and the presence of metals, ions, and disinfectants affected the stability of a live Salmonella vaccine (i.e., Elanco’s live attenuated bivalent vaccine AviPro Salmonella Duo) over a 24-hour period. While many water characteristics had minimal impact, elevated levels of certain metals and disinfectants were found to inactivate the vaccine.

The study was conducted by Elanco researchers and published in MDPI Poultry.

Metals Identified as Primary Risk to Vaccine Stability

Among the parameters tested, aluminum, arsenic, iron, and manganese had the most pronounced, dose-dependent negative effects on vaccine survival. In contrast, fluoride, nitrate, sulfate, and water hardness exerted little to no measurable influence under the tested conditions.

Iron concentrations as low as 0.5 milligrams per liter (mg/L)—levels well within existing livestock drinking water guidelines in some countries—led to a decline in vaccine counts. Manganese levels of 1 mg/L also jeopardized vaccine efficacy, depending on exposure time and temperature, despite also being within recommended thresholds for farm animal water in certain countries.

At higher concentrations, aluminum and arsenic also reduced vaccine viability. However, the researchers noted that adverse effects from arsenic occurred above the 10 micrograms (µg)/L limit set for human drinking water in many countries, suggesting that municipal water supplies within regulatory limits would likely not pose a risk. Groundwater sources in regions with elevated environmental arsenic levels could present greater concern.

Because poultry operations frequently rely on borehole or well water, which can contain elevated metal levels, the researchers suggest that chemical testing should be considered before administering live vaccines via drinking water.

Disinfectants Rapidly Inactivated the Live Vaccine

The study evaluated commonly used drinking water disinfectants: free chlorine, chlorine dioxide, and hydrogen peroxide. All of the studied disinfectants strongly reduced vaccine viability within a short period, even at concentrations considered safe for poultry consumption.

Hydrogen peroxide inactivated the vaccine quickly, and the tested water stabilizer did not provide protection. On the other hand, the stabilizer did mitigate the effects of chlorine and chlorine dioxide up to certain concentrations.

The researchers suggested that residual disinfectants from prior water line sanitation or municipal supply spikes could unintentionally compromise vaccination efforts if not monitored and managed. They advised ensuring that disinfectant treatments are paused and verifying residual levels before live vaccine administration.

pH, Hardness, and Ions Showed Limited Impact

The vaccine demonstrated resilience across a broad pH range, with significant declines observed only at pH 4 and pH 9. Water hardness, conductivity, and most dissolved ions had minimal influence on stability. Chloride showed a dose-dependent effect at high concentrations, although vaccine levels remained within manufacturer specifications under the tested conditions.

These results suggest that routine fluctuations in many water quality parameters are unlikely to compromise vaccine performance, given that values remain within moderate ranges.

Implications for Food Safety and Biosecurity

Live Salmonella vaccines administered via drinking water are widely used in poultry production because they stimulate mucosal and cellular immunity and can be applied early in life without handling stress. Effective vaccination is considered a core component of tertiary biosecurity measures that enhance flock immunity, thereby reducing pathogen colonization and shedding.

Because Salmonella can persist in poultry populations and farm environments for extended periods, compromised vaccine viability could increase the risk of downstream contamination of meat and eggs.

The researchers concluded that maintaining appropriate chemical and disinfectant conditions in drinking water lines is critical to ensuring vaccine efficacy. While water stabilizers may provide protection under certain conditions, they did not fully mitigate risks from all contaminants, especially hydrogen peroxide.

As the study was conducted in vitro, the researchers noted that field validation is necessary. However, the data provide practical information for poultry operations seeking to strengthen vaccination programs and reduce food safety risks pre-harvest.