depending on their age, they often are suffering from e.coli scours(usually those 8-9 days or younger)or rota/corona virus infection(those 8-9 days or older). proper colostrum management(particularly scourgard vaccinated cows), use of passive antibodies given orally(first defense boluses), and correct antibiotic usage are all important. but firstly it is most important that they have the lost fluids and electrolytes replaced.
those affected by e.coli have undamaged intestinal villi, so they usually will respond to oral fluids(a summary of this topic and how to assess the calf can be found at http://www.acornemb.com/scours.htm - it is typically why i will ask if a calf can stand on it's own)and a good dose of probiotics. those with viral scours can have damaged villi and oftentimes giving IV or SQ fluids is a way to bypass that damage and assure that dehydration and acidosis that have developed are reversed. SQ fluids can be given easily on the farm to a calf that is weak, but can still stand on it's own with help. Key point is to be sure they are warmed up completely before administering - cold fluids under the skin will sit there and not absorb quickly - and that is no help.
don't take them off of milk at this time(dairy calves) - electrolytes are helpful certainly, but they still need the energy and calories supplied by milk. i have come across calves that have lost tremendous amounts of weight but have their hydration restored - remember that these youngsters have a slim margin of reserve and particularly in cooler weather they can use this up quickly. don't worry about the scours extending a day or two extra - remember that if you replace in the front what is coming out the back they will cope with it fine and work through this episode.
