1-  Fecal examination for demonstration of parasitic enteritis

2-  Pathogen isolation and characterization along with histopathology as the gold standard for etiologic agent and disease confirmation

3- Direct visualization (e.g., light microscopy) of pathogens in feces or intestinal contents as well as the detection of antigens (e.g., Ag-ELISA).

4- Post-Mortem Examination: In severe cases where calves die, a necropsy can help identify the underlying cause.

Sampling and specimen submission

1- Proper specimen collection and delivery to a diagnostic lab is commonly neglected, and significantly impacts the diagnostic outcome.

2- samples for diagnostic testing should include

A. faces from acutely diarrheic animals prior to therapy

B. blood samples.

C. Necropsy specimens from freshly sacrificed, moribund, or euthanized calves are of great value for diagnosis during severe outbreaks.

Guidelines for sample collection for diagnosis of diarrhea.

1-  Fresh fecal samples should be directly recovered from diarrheic animal into a specimen container with either rectal swabs or by rectal stimulation while avoiding environmental contamination (by soil, urine, or other feces). Once collected, the sample should be stored in a transporting medium or special stool container with refrigeration to maintain pathogen viability and sample integrity (e.g., reduced overgrowth of undesired bacteria and prevention of nucleic acid degradation). Samples of anaerobic bacteria (e.g., C. perfringens) should be kept in an oxygen-free transport medium during shipping if possible.

2- Fresh and formalin-fixed gastrointestinal tissues (abomasum, small intestine, or colon) including regional lymph nodes and liver should be collected along with colonic contents.