Diarrhea is one of the most important health and life-threatening cases in the first days after the birth of calves, which occurs under the influence of a set of management and environmental factors. Following the occurrence of diarrhea among neonatal calves, a number of dairy herds around Mashhad were visited and sampling of diarrheal cases was done along with blood sampling from 2–7- day old calves. Cryptosporidium contamination in diarrheal calves was confirmed in the laboratory examination of stool samples. The protozoan Cryptosporidium parvum is one of the most important pathogens in newborn calves causing diarrhea, dehydration, and abdominal pain. Investigations have shown that the occurrence of disease among dairy herds due to the continuity of births throughout the year and poor hygiene practices in newborn calf care, is constantly ongoing. Evaluation of serum total protein of 2-7-day-old calves revealed the failure of transfer maternal immunity (TP<5.2gr/dl) in herds. Calves acquire maternal immunity only after receiving colostrum, because the cotylodon- coronicle structure of the cow placenta does not allow the passage of large molecule compounds, including antibodies during the pregnancy period. The failure of transfer maternal immunity to calves at the herd level is one of the management factors that affect health and the occurrence of diarrhea. Some studies have shown that colostrum antibodies, including high levels of IgG, do not have a significant effect against intracellular pathogens, but eating high-quality colostrum (IgG>50gr/L) due to the presence of other cellular-immune components at least 10% of body weight during the first 4 hours of life, along with proper umbilical cord disinfection and separating the calf from the mother immediately after birth, will guarantee the calf’s health and prevent neonatal diarrhea cases to a very large extent

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