Geni WrenDehydration and acidosis are the keys when treating diarrheic calves. Diarrhea increases the loss of electrolytes and water in the feces of calves and decreases milk intake. This results in dehydration, strong ion acidosis, electrolyte abnormalities (usually decreased sodium and increased or decreased potassium), increased D-lactate concentrations, and a negative energy balance (from anorexia and malabsorption of nutrients). Therefore diarrhea is by far the most common indication for fluid therapy in neonatal calves.
Geof Smith, DVM, MS, PhD, Dipl. ACVIM, North Carolina State University, says we see some diarrhea in young calves (around 5 days of age) but it seems like the majority of cases are 7–14 days of age. “There’s a magic window for diarrhea on many dairy farms right around day 8–10,” he says. “You can have diarrhea in older calves — but once we make it past 2 weeks — most farms seem to do okay.” (see “Treatment decision tree,” under Practice tips.)
Best methods for assessment
The most accurate methods for assessment of dehydration in calves are eyeball recession into the orbit and skin tent duration in the neck region. Smith says to gently evert the lower eyelid and estimate the recession of the globe into the orbit. Skin elasticity is best measured on the lateral side of the midcervical area by pinching a fold of skin, rotating it 90°, and measuring the time for the skinfold to disappear.
Wendy Savage, NCSUGeof Smith, DVM, PhD, Dipl. ACVIM Smith adds all other methods of assessment are inferior to these two methods. Those methods include things like mucous membrane color or dryness (how they feel), capillary refill time and packed cell volume (PCV). “These are things commonly used in horses and small animals but don’t seem to work well in calves,” he explains. The best laboratory test is change in plasma protein concentration, which he says is better than hematocrit.
Based on physical exam (eyeball position, depression score) most of the time Smith will go ahead and give oral fluids. “To do lab work you’re going to have to draw blood, drive back to the clinic, run the lab test and then head back out to the farm,” he says. “The main exception is folks that do a lot of haul-in work at their clinic; then lab work is fairly easy to do quickly.” He says a total protein value at a practice is pretty easy to get by spinning down blood and using a refractometer. “But not too many ambulatory vets have a centrifuge in the back of their trucks.”