Protist community sites and structure under two barn management systems at a commercial dairy.

Introduction: Investigations into the location and load of protists in the environment arounddairies are scarce but are essential to maintaining the health of livestock.Moreover, the design of dairy barns has fluctuated over the decades to maximizecattle health and milk production without regard to influences on environmentalmicrobiomes. Beyond cost, the major emphasis of barn design is the managementof appropriate temperature and comfort for cattle. However, there havebeen no corresponding investigations into whether these design changes affect protist communities within barns. Methods: In this study, community shotgun metagenomic analysis was used to define the spatial composition and relative abundance of protist communities from 118 samples of manure, lagoons, troughs, and house and stable flies at a commercial dairy implementing two free-stall management systems: flow-through and cross-vent. Sequence reads were mapped to the CosmosID database. Viability was not assessed; therefore, results reflect DNA detection only not viability or disease occurrence. Results: The protist composition differed significantly between dairy components. Ecological findings showed that troughs and lagoons harbored high protist diversity, including the possible pathogen Neobalantidium coli and potential carriers Paramecium biaurelia and Acanthamoeba. Manure had the lowest protist diversity. Stable flies carried more protist taxa than house flies. Both fly species uniquely carried the non-pathogenic alveolate parasite Hammondia hammondi. The water mold plant pathogen Pseudoperonospora cubensis was identified in all sample types. Of the total relative abundance of protists, 2.10% were amoebas, 7.63% alveolate parasites, 62.71% water molds, 23.31% ciliates, 1.74% foraminifera, and 2.50% diatoms. Discussion: These results describe preliminary spatial overlaps and possible avenues of dissemination, providing a basis for assessing appropriate management systems and identifying protist reservoir sites within dairy operations.