Tactile stimulation by humans: Do pigs prefer scratching or stroking?

Abstract

Scratching and stroking are tactile interactions used to improve the animal-human relationship and reduce stress in pigs. Both interactions resemble behaviours from the behavioural repertoire of pigs and have been applied in previous studies. To investigate the relative efficacy of these tactile interactions in eliciting positive emotions, we examined pigs’ preferences for one of these interactions. Twelve recently inseminated gilts habituated to human contact were trained to discriminate between two handlers standing in two different locations in their home pen. One handler was providing stroking, the other one scratching. After 5 weeks of training, the pigs were tested for their preference. According to the preference index calculated based on the time the pigs spent being stroked and scratched, they did not significantly prefer one type of contact (p = 0.182, preference index median = 0.09, with −1 indicating an absolute preference for stroking and 1 an absolute preference for scratching). There was no significant difference between how often the pigs chose to approach the scratching or the stroking handler (p = 0.115, median scratching = 3.0, median stroking = 1.5), and neither did they approach one of them significantly earlier than the other (day 1: p = 0.126, median of difference between latency to approach scratching handler and latency to approach stroking handler = −55 s; day 2: p = 0.148, median of difference between latencies = −27 s). We did not find evidence for a general preference of one type of contact over the other. To improve the animal-human relationship, it might thus be most efficient to offer both types of tactile contact and adjust the contact depending on the pig’s behaviour indicative of enjoyment.