Effect of Drinking Water Distribution System Design on Antimicrobial Delivery to Pigs

SIMPLE SUMMARY: The piped water system in buildings that house growing pigs is used on many farms for short periods to medicate pigs with antimicrobials, in order to keep them healthy and productive. However, the effect that the design of a building’s water system has on antimicrobial delivery to pigs in pens throughout the building is not known. Thus, we tracked the antimicrobial concentration in water available to pigs at four drinkers during four in-water dosing events, each conducted with looped water systems differing in their design. We found that the water system’s design and the pigs’ water usage and drinking patterns had a large influence on water flow and, therefore, the amount of antimicrobial delivered to pigs in each pen over time. We discovered that by using a circulator pump in a building’s looped water system, all pigs within a building could be delivered the same antimicrobial concentration in water over time. We also showed how a hydraulic modelling tool can be used to predict the antimicrobial concentration at drinkers over time in a specific building during a dosing event. This provides an opportunity to compare alternative in-water dosing schedules for pigs in a given building and select the one likely to be the most effective. ABSTRACT: On many pig farms, growing pigs are mass-medicated for short periods with antimicrobial drugs through their drinking water for metaphylaxis and to treat clinical disease. We conducted a series of four prospective observational cohort studies of routine metaphylactic in-water antibiotic dosing events on a commercial pig farm, to assess the concentration of antimicrobial available to pigs throughout a building over time. Each dosing event was conducted by the farm manager with a differently designed looped water distribution system (WDS). We found that the antimicrobial concentration in water delivered to pigs at drinkers in each pen by a building’s WDS over time was profoundly influenced by the design of the WDS and the pigs’ water usage and drinking pattern, and that differences in the antimicrobial concentration in water over time at drinkers throughout a building could be eliminated through use of a circulator pump in a looped WDS. We also used a hydraulic WDS modelling tool to predict the antimicrobial concentration at drinkers over time during and after a dosing event. Our approach could be used to evaluate alternative in-water dosing regimens for pigs in a specific building in terms of their clinical efficacy and ability to suppress the emergence of antimicrobial resistance, and to determine the optimal regimen. The approach is applicable to all additives administered through drinking water for which the degree of efficacy is dependent on the dose administered.