Assessing dehydration status is the first step in managing a scouring calf, but it’s not as simple as assigning a percentage. Dehydration, acidemia and neurologic function do not progress at the same rate. A calf may not look profoundly dehydrated but still require intravenous correction.
Speaking at the AABP Recent Grad conference, Dr. Blake Balog, professional services veterinarian with TELUS Agriculture, outlined some tips for assessing hydration status in calves.
1. Start with the Eye
Globe recession remains one of the most reliable field indicators of dehydration, but only if it is measured correctly.
Balog recommends rolling down the lower eyelid to look for space.
“Make sure when you’re assessing that you’re rolling that lower eyelid out to a more normal position and measure that depth,” Balog says. “If it’s hitting somewhere in the 4 mm range, that’s going to be close to 8% dehydration, which is the point where we want to use IV fluids.”
Measure deliberately and determine whether oral fluids will be enough.
2. Check Peripheral Profusion
As dehydration progresses, circulation shifts centrally and causes the extremities to cool. While you could invest in an infrared thermometer, using your hands to feel whether the peripheral distal limbs are cold or cool will likely suffice.
Cold limbs alone may not indicate dehydration, but they certainly reinforce that it may be the case.
3. Separate Dehydration from Acidemia
“The level of dehydration doesn’t always linearly go along with the level of acidemia,” Balog says.
This is a crossroads at which decisions can go wrong. A calf may not appear severely dehydrated and still be acidemic. Relying on percent dehydration alone can miss calves that require escalation.
Balog suggests testing the palpebral reflex.
“When you tap that medial canthus and you get a delayed or sluggish palpebral reflex, that’s an indicator of lactic acid that’s accumulated in that animal,” Balog says.
Delayed reflexes, weakness and failure to suckle suggest metabolic compromise. If the calf cannot suckle, oral therapy alone is unlikely to be enough.
4. Use Supporting Findings
Urine concentration can reinforce your assessment. If a refractometer is available, specific gravity could be used. Otherwise, dark, concentrated urine supports systemic dehydration.
Skin tenting is another quick way to evaluate hydration. Pinch a fold of skin on the neck or around the eyes and count the number of seconds it takes to flatten. Skin flattening in less than 2 seconds indicates normal hydration, 2 to 5 seconds to flatten indicates 8% dehydration and over five seconds would indicate severe dehydration over 10%.
Placing an IV Catheter in Calves
Placing an IV catheter in a dehydrated calf can be more difficult because the skin is thick and the jugular vein does not present well.
Balog recommends focusing on mechanics.
Position the head on a downward slope.
“We’re going to have the head of that calf dropping downward. That’s going to help fill the jugular vein a little bit easier,” Balog says.Lowering the head improves venous fill and simplifies placement.
- Clip and prep generously.
Dehydrated skin offers more resistance. A wide clip and thorough prep make catheter passage smoother. Perform a cut down incision.
“This is the key part that I think we’ll struggle with: Not doing a cut down. Cut down to me is not sawing with the scalpel blade down toward the jugular. We’re going to tent the skin up and we’re going to go straight down with our 22 blade until it finally releases through there and then we’re going to lay that down,” Balog says.This incision is vertical and controlled, not a sweeping motion toward the vein. This is critical in dehydrated calves when the skin is super thick and difficult to get through.
- Secure the catheter carefully.
Tape and suture so access remains stable during fluid delivery. Balog likes to use a butterfly catheter secured with a couple sutures. He’ll then do an additional suture up on the head so the line remains straight.
The goal is straightforward: assess accurately and intervene appropriately. When dehydration approaches 8% or acidemia affects function, oral therapy may not be sufficient. At that point, gain access, deliver fluids and reassess.
