Do pigs mourn over their losts?

Answer 1

Yes. GUinea pigs are very social and docile creatures that will indeed be sad. IF your guinea pig has recently lost their partner/s you should give then extra attention. If that doesn't help you can buy new little toys. And maybe even introduce new pigs. Introducing a diffrent age male guinea is very hard. Introuducing a diffrent age females is really easy although.

Answer 2

Anecdotal evidence of animals pining for the loss of a close companion may tell you yes. However, the emotional level of such animals are not well understood to give an unambiguous, scientific answer to this question which will confirm or deny the hypothesis if farm animals grieve the loss of their dead.

It has been observed that, however, animals will grieve for the loss of a herd or flock member, but it is a brief moment and one that sustains itself over a much shorter period of time than the kind of grief experienced in humans. Also, the level of emotional grief experienced by such animals is much more subtle than what is noticed in humans.