Cryptosporidia on dairy farms and the role these farms may have in contaminating surface water supplies in the northeastern United States

The prevalence and risk factors for shedding of cryptosporidia by dairy cat tle and calves and the prevalence and risk factors for cryptosporidia in su rface waters associated with dairy farms were determined for a well-defined watershed in the northeastern United States. Eleven dairy farms were enrol led in the study and subjected to monthly sampling over a 6-month period. A nimal-, water-, and manure-management practices were determined by survey a nd fecal, on-farm water, and stream samples were obtained monthly and evalu ated for the presence of cryptosporidia. Ninety-one percent of the dairy fa rms in our study had Cryptosporidium on their premises. Fifteen percent of the sampled calves 0-3 weeks of age were shedding cryptosporidia. The risk factors for calves shedding cryptosporidia were contact between calves and frequent bedding changes. The probability of shedding cryptosporidia decrea sed with age. Nine percent of farm-associated stream samples were cryptospo ridia-positive. The single risk factor for detecting cryptosporidia in surf ace water was increasing frequency of spreading of manure on fields. The pr obability of detecting cryptosporidia in streams decreased as 5-day cumulat ive precipitation increased. There were no animal-associated or barnyard-ma nagement features associated with detecting cryptosporidia in farm-impacted streams. (C) 2000 Elsevier Science B.V. All rights reserved.