Tail postures and tail motion as indicators of animal welfare in pigs

In general, the tail can provide useful information about physical and emotional experiences at a given time.

The following etogram includes every tail posture and movement observed in domestic pigs:

These positions were assigned in four quadrants of the “circumplex model of emotions” indicating on the vertical axis the level of activation (excitation) and on the horizontal axis the level of liking/disliking (valence)

Interpretation of postures and tail movements
Although there are exceptions in each quadrant (i.e. valency-excitation combination), in general, in domestic pigs, it can be assigned:

A curly/rippled tail to the positive valence and high excitation quadrant, while a relaxed tail that hangs but moves freely can be assigned to the positive valence and low excitation quadrant.

A hidden stationary tail can be assigned to the negative valence and low excitation quadrant when it is chronically (semi-)folded; and to the negative valence and high excitation quadrant when it is a sudden response to a potential threat.

In conclusion, there is a large amount of literature on tail posture and motion that can help to correctly interpret pig tails in terms of the animal’s experience.

References

Irene Camerlink, Winanda W. Ursinus. Tail postures and tail motion in pigs: A review. Available online 26 July 2020. https://doi.org/10.1016/j.applanim.2020.105079