A. The color of the diarrhea may not be diagnostic to the pathogen causing the scours, but since the calves are anywhere from 7 to 10 days the top pathogens could include rotavirus, coronavirus, salmonella and clostridium. The best way to determine the pathogen would be to send in some fecal samples or necropsy of the calf.
For treatment, you should always give fluids to scouring calves, the sooner the better. An additional feeding of electrolytes either once or twice a day in addition to their milk is a good way to rehydrate the calf. You might also need to give IV fluids (lactated ringers) on a case by case basis. In addition to fluids, it is prudent to give them a broad spectrum antibiotic which should be discussed with your veterinarian.
Perhaps the most important key to answering this question is prevention. A review of your colostrum program should be done to ensure calves are getting the optimum maternal colostrum. You may also want to consider adding certain vaccines to your dry cow program. Some vaccines will enrich colostrum with antibodies to protect against pathogens causing the diarrhea in calves. A veterinarian can help review your dry cow and calf management programs and make any necessary recommendations.
But, remember for treatment it’s all about hydration for scouring calves in addition to a broad spectrum antibiotic. And be sure take another look at your colostrum program- you may be able to eliminate problems before they arise.