Diarrhea caused by Cryptosporidium spp. is a commonly encountered disease of neonatal dairy calves. The organism is extremely resistant to inactivation and is therefore endemic on the majority of dairy farms worldwide. Exposure to the organism is inevitable, but the development of clinical disease depends on environmental factors such as temperature, ventilation, hygiene and plane of nutrition. Pre-weaning plane of nutrition has recently been identified as a key factor in the short- and long-term health and performance of dairy cattle, but traditionally, calves have been energy-restricted in the pre-weaning period. Ad-libitum feeding strategies that address the pre-weaning plane of nutrition are gaining in popularity; two examples are computerized on-demand feeding technology and acidified milk/mob-feeder systems. A local dairy transitioned to an acidified milk system and subsequently experienced an outbreak of cryptosporidiosis in the pre-weaned calves. Possible causes for the outbreak include the interaction of stress and inadequate energy.