Prevalence and concentration of Cryptosporidium oocysts in beef cattle paddock soils and forage

Cryptosporidium is a parasitic protozoan of great interest because of its widespread occurrence in surface waters, high degree of infectivity, and difficulty of risk management associated with its presence and control. Information about environmental loading and seasonal prevalence of Cryptosporidium oocysts is important for development of watershed management plans to protect public health. Healthy adult beef cattle are known to shed oocysts into the environment, and Cryptosporidium oocysts are often present all year in streams and groundwater in livestock agriculture areas. Surface soil and forage samples from 12 Virginia, United States, paddocks were analyzed bimonthly over 3 years for the presence and concentrations of Cryptosporidium oocysts. Half of the paddocks were grazed by stocker beef from November to September. The other half were managed for hay, but were grazed for a few days by the same animals in late fall and early spring to clean up late fall forage regrowth. Annual mean oocyst prevalences in soil were 57.9% and 48.4% in pasture and hay paddocks, respectively. Mean annual oocyst prevalences on forage were 52.4% and 40.5% in pasture and hay paddocks, respectively. Prevalence and concentration of oocysts on hay forage was highest in summer. Oocyst concentrations increased with increasing prevalences in both management systems. Wild animals appeared to be efficient vectors for oocyst distribution among paddocks. Canopy management, short-cycle rotational grazing, and control of wildlife are potential strategies for reduction of Cryptosporidium oocysts in pasture and lessening risk of contamination of water supplies, but further studies are needed before recommendations can be made.