Blood samples offer a myriad of data to help you manage your calves, says Jerry Bertoldo, veterinarian and
When done correctly, blood draws can be done with a minimum of stress to both people and calves. With that in mind, Bertoldo offers the following steps for collecting good blood samples.
1. Choose the correct needle.
Calf blood vessels are not very large. Experts recommend using a 1-inch long, 18-gauge needle to draw blood from calves. Use a new needle for each calf. If that is not practical on your operation, change needles every few calves for biosecurity reasons.
However, change the needle immediately if it develops a barb at the tip or if it becomes too dull to easily insert.
Use a plastic disposable syringe (a 6- or 12-cubic centimeter is easiest to handle) or a serum vacuum tube — commonly called a red top — to collect the blood sample. If you use a vacuum tube, you will need a special transfer needle and a holder. These needles are usually 1.5 inches long X 20-gauge. Often, these can be ordered in tandem with the vacuum tubes. All of these supplies can be ordered through your local animal-health supplier or mail-order catalog.
2. Restrain the calf.
Calmly back the calf into a corner or against a wall and press your hip into her shoulder. Place your leg in front of her front legs to hold her in place. If you’re tall enough, you can straddle the calf’s neck to hold her in place. Hold her head to the side so she doesn’t impede your actions, or use a halter if you prefer. You should be able to do this on your own, but use a partner if you need help to reduce stress on you and the calf.
3. Find the jugular vein.
Place your hand on the side of the calf’s neck just behind the base of her jaw and feel for the groove where the jugular vein is located (as shown above with an anaesthetized calf). There is one of these large vessels on either side of the neck that carry blood from the head back to the heart. Gently press against the jugular in the lower part of the neck to slow blood flow. This causes the vein to slightly enlarge, making it easier to see and insert the needle.
4. Insert the needle.
With one hand still gently pressing on the jugular, use the other hand to place the needle parallel with the vein and insert it into the enlarged portion of the vein (with the syringe attached). For correct placement, the insertion angle must be nearly flat.
Push the needle in about 0.5 inch — half of its length — and slowly pull back on the syringe’s plunger. If you have correctly positioned the needle, blood will immediately begin to flow. If blood does not flow, gently and slowly pull the needle out until blood does flow. (You may have poked through the vein.) Never press down on the plunger. Pull back with a slow, steady motion. Try to get at least 3 ccs of blood into the syringe.
5. Similar steps for a vacuum blood tube.
Use the same steps when using a vacuum blood tube. Find the jugular vein and insert the needle attached to the holder without the tube attached. When you have placed the needle where you want it, push the tube into the needle. Again, if you’ve hit the vein, blood will flow immediately. If not, gently maneuver the device until blood does flow. Remember that the vacuum in the tube will be lost if the needle is pulled out of the skin with the tube attached.
6. Wrap up.
Once you’ve obtained an adequate blood sample, remove the needle and syringe or tube and apply pressure to the point of entry for a few seconds. Use an alcohol swab to remove any residual blood. Then, carefully identify the blood sample and store it correctly.
Draw air in and out of the syringe with the needle attached to eliminate residual blood in the syringe. Wipe the needle with an alcohol-soaked cotton swab to reduce blood-borne disease transmission. Or, discard used needles properly.
Now, you’re ready to move on to the next calf.
As with any new technique, it takes time to become comfortable and master the steps. Don’t get discouraged if the first one or two don’t go smoothly. You may just need a little practice.