I've not come across any scholarly articles on pigs as such, but the general thought seems to be that animals can eg
http://www.thenakedscientists.com/HTML/questions/question/2367/this, but from personal experience pigs can display the same symptoms, although whether this is physiological or psychological would be open to debate.
Some of our sows go "off" for a period after giving birth. Ignoring food is frequent in the first few days, occasionally some just look miserable, but these are more than outweighed by good happy mums, who tend to their offspring.
I s'pose one of the advantages of pigs is that apart from feeding, mum doesn't need to do a lot, and if she is feeling "off" as long as she lies there the piglets can feed, not like say a sheep or dog, who needs to clean their offspring etc.