Concerning the rangeland cow/calf project that many of you collaborated on, we have finished testing the final herd for Cryptosporidium parvum and Giardia spp. One fecal sample was collected from 25-45 animals per herd, with about half being calves and half being cows and a few heifers. In all, 39 herds were visited and 1462 cattle tested. Herds were both spring and fall calving which resulted in the calf ages ranging from 1-12 months and both dry and pregnant cows.

Preliminary findings were that only 4% of the 1462 cattle were shedding C. parvum oocysts and 44% of the 39 herds had one or more individual cattle shedding. Herds shedding C. parvum oocysts were located throughout California. Although this point prevalence of shedding would likely have been higher had we tested only spring calving herds or tested each animal more than once, this low prevalence of shedding suggests that cow/calf herds are not heavily infected with C. parvum in the spring. More detailed analyses are underway and should be concluded in +/- 4 months.

Concerning Giardia spp., 27% of the 1462 cattle were shedding cysts and 95% of the 39 herds had one or more individual cattle shedding. This was a surprise finding and the point prevalence of shedding would likely have been even higher had we tested each animal more than once. As with C. parvum, more detailed analyses are underway and should be concluded in +/- 4 months. The ability of these bovine-derived Giardia cysts to infect humans is unknown at this time. There has been considerable controversy in the scientific literature over the ability of Giardia cysts obtained from domestic and wild animals to infect humans. Giardia will be the subject of a detailed newsletter in the future.

Rob Atwill, DVM, MPVM, PhD
Tel: 209-688-1731 ext 218
Fax: 209-686-4231
E-mail: ratwill@vmtrc.ucdavis.edu