Dominance?

[Alicia]

I have 2 sows, Edie and Marmalade. They are both about 1 or 2 years old (not exactly sure) and until last month they lived with another sow, Amber. Marmalade's always seemed to be the dominant one, but I noticed today they've been chasing each other again and making that purring noise. Is that because a guinea-pig has died they are resorting the dominance? They aren't fighting or anything so I'm not really worried but I was just wondering why they are doing this.

 

[Freela]

I've heard that any sort of change (adding or removing a pig) can shake up the hierarchy so they need to establish dominance again. I also notice this kind of dominance behaviour whenever one of my sows is in heat. Even the less dominant pig will start pushing boundaries and being bossy when she's in heat and there is more conflict there, though it's all for show and never leads to actual fighting.