Pastoralism,Research, Policy and Practice, 2016; 6 (13)Diarrhoeal diseases can be debilitating, especially for children and young animals. In many rural areas, particularly pastoral communities, livelihoods are characterized by close interaction between household members and their livestock herds, and children often care for young animals, creating opportunities for the transmission of multiple zoonotic pathogens. Using a One Health approach, we first evaluated whether diarrhoeal diseases were a problem for pastoral households in Tanzania and then investigated their calf herds to identify the prevalence and risk factors for diarrhoeal disease and the shedding of the zoonotic pathogens Cryptosporidium and Giardia. Sixty percent of households reporting cases of human diarrhoea also had diarrhoea detected later in their calf herds, and calf herds shedding Cryptosporidium oocysts were six times more likely to be diarrhoeic. Because Cryptosporidium shares a similar transmission mode with a wide range of diarrhoeagenic organisms and calf diarrhoea outbreaks can involve multiple pathogens with mixed infections, it is possible that calf diarrhoea may be indicative of shared risk of zoonotic pathogens from environmental contamination. To mitigate the risk of transmission of faecal-borne zoonotic pathogens from herds to households (boma-livestock pens to banda –household building), we describe a conceptual disease early-warning method proposing diarrhoeic calves as animal sentinels. Such a calf warning system, combined with appropriate interventions designed to minimize exposure, could serve as a practical solution for reducing risks of diarrhoeal diseases among animals and people.