Blood collection in the conscious miniature pig can be a challenge. Peripheral veins are not readily accessible and some vessels, such as the auricular vein, are inadequate for obtaining sufficient volume from some individuals. The cephalic vein is also difficult to access, often requiring a cutdown through the overlying thick skin in adult pigs. Additionally, collection from the more commonly used jugular vein in a conscious animal can be associated with complications, such as hematoma formation, thyroid gland damage, or even the occasional death. The stress induced by restraint required for jugular vein access can also be problematic.
The radial vein is located along the medial aspect of the forelimb. This vessel is relatively straight and generally superficial (Fig 1).
Radial vein blood collection can be successfully employed in pet mini pigs without complications and with minimal stress, particularly when a food distraction is offered. Use of a sling can facilitate blood collection if the pig is acclimated to the device, as the animal cannot see the technician and can be distracted with food treats (Fig 2). Often the pig has no reaction to needle insertion or manipulation of the limb. The vein is also easily accessed when the animal is placed in dorsal recumbency, such as in a V-trough. (Although, of course, a food distraction should not be attempted when the animal is on its back).
- Restrain the animal and apply pressure to the medial aspect of the proximal forelimb, near the axillary region, to occlude the vein (Fig 3 red arrow).
- The phlebotomist grasps and stretches out the limb, with a thumb on the caudal aspect of the leg.
- Palpate the caudal edge of the antebrachium and the small, rounded accessory carpal bone along the caudal aspect of the limb (Fig 3 red circle), which can be felt as a little “lump” just above the dew claws. The radial vein lies in a groove between these two landmarks (Fig 1). The vein is sometimes visible in young or light-colored animals, but more commonly the vein is neither visible nor palpable.
- Insert a 1-inch 22-gauge needle parallel to the long bone (Fig 4). Rapid clotting can create difficulty with smaller gauge needles.
- Apply gentle, steady negative pressure to obtain the desired volume. The radial vein is large enough to facilitate collection of a significant volume of blood (e.g. 3-6 ml). Apply only a small amount of suction, particularly if a larger syringe (i.e. 6 ml) is used to prevent collapse of the vessel.
- “Pumping” or slowly applying and releasing pressure at the site of occlusion can aid sampling.
It is not known whether the radial vein lends itself to the repeated collections required by some research protocols, but the vessels extends along the length of the limb. If the initial sample is taken distally, subsequent samples can theoretically be taken at progressively more proximal points.
The radial vein, located along the medial aspect of the forelimb, is readily available for blood sampling in the miniature pig. The radial vein provides easy and safe peripheral venous access.