While considering the economical, as well as ethical aspects, the average age of our cows is far too low. The average culling age of dairy cows in Finland is 4.9 years, and when a cow is removed from a herd, it has calved 2.5 times on average. Economically optimal results would be reached when the cows achieves a calving average of 4, and with a 20–30 % culling rate. The culling rate is influenced by the targets set by the farmer, as well as the disease incidence of a herd. Planning an eco-nomically sustainable culling and replacement strategy is part of the herd health management of a farm.
Waterborne outbreaks caused by zoonotic protozoans, Cryptosporidium parvum, Giardia intestinalis and Toxoplasma gondii, have led to pub-lic health concern and economical losses during the past decades in industrialized countries. The infective forms of these parasites are exc-reted in feces, leading to contamination of surface and ground water mainly by sewage effluent or manure run-off. To prevent waterborne outbreaks, the overflow of infective parasite forms to water has to be controlled.