Teat massage after milk ingestion in domestic piglets: an example of honest begging?

After milk ejection, piglets spend several minutes massaging their own teats on the sow. We examined whether this behaviour could be a mammalian counterpart to begging in young birds, and hence be explained by theories of honest begging. In one experiment, the behaviour of piglets was examined in relation to their previous milk intake. In each of 16 litters, one focal piglet was exposed to three treatments for three consecutive sucklings: 'no milk', where the piglet was withheld from the teat during milk ejection; 'extra milk', where it was fed 10 ml of extra milk directly after milk ejection; and 'control', when it received its normal intake. Average massage duration in the next three sucklings was significantly longer in the 'no milk' than in the control piglets. 'No milk' pigs massaged more intensely (number of massage movements/min), were more persistent in attempting to maintain udder contact and spent less time away from the udder. However, there were no significant differences between 'control' and 'extra milk' treatments. In a second experiment, in which we manually massaged teats for 0, 3 or 10 min, we found no significant effect of massage duration on milk output (measured by weighing piglets before and after milk ejection), although massage tended to increase output. We conclude that post-sucking massage in piglets has a number of aspects similar to honest begging in birds. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.