We take hold of one of the sow's ears with a pig holder (one with a long bar preferably) and we pull slightly. The sow stays still when she feels the hold and starts screaming, and we take advantage of her mouth being open to take hold of her upper jaw with another pig holders and to immobilise her.
This trick allows to immoblise the sows quickly in their cages to draw blood from them.
The job of drawing blood from the sows to obey the established health regulations or to study diseases is sometimes a chore, because the sows refuse to stand still, especially the ones that have had blood drawed from them previously, and they constantly hide their snout between the bars of the cage and they are even able to 'spit' the pig holder with which we take hold, with great difficulty, of their upper jaw.
In these cases, the stress caused to the animal exceeds that of the drawing of blood that, if well performed, only takes a few seconds, and it also exasperates the farmer that tries to immobilise the sow.
When this happens, it is very easy to take hold of one of the sow's ears, because it is big and easy to reach.
When the sow feels the pull on her ear, she has a reflex similar to that when we hold her upper jaw, and she starts to show her 'disagreement' with screams similar to those when we use the upper jaw technique.
Just then, it is very easy to take hold of her upper jaw perfectly, so the immobilisation time drops drastically.