Agriculture Reference
In-Depth Information
Sow starts grunting,
lies on side
Piglets assemble
and massage udder
Increased grunting,
oxytocin release
Piglets switch to
slow sucking
Oxytocin reaches
mammary glands,
milk ejection
Fast sucking,
milk ingestion
Piglets resume
udder massage
Sow rolls on belly
or stands up
Piglets fall asleep
or leave
Whichever comes
rst
Nursing termination
Figure 13.1. Structure of a pig nursing with milk ejection (adapted from Fraser, 1980).
grunting. The ensuing phase is the pre-massage, during which all or most of the piglets
intensely rub the vicinity of 'their' respective teats and occasionally suck at them. Some
of the piglets may interrupt the massage by going to the snout of the sow where they
emit short series of 'croaking vocalisations' while in naso-nasal sniffing contact with
the mother.
After 1-3 min of teat stimulation, the posterior part of the pituitary gland (neurohypophysis)
discharges a surge of oxytocin which, upon reaching the mammary glands via the
bloodstream, triggers the crucial phase of milk ejection (Ellendorff
et al.
, 1982). Milk
ejection in pigs lasts only 20 sec on average. Physiologically, the burst of oxytocin makes
the myoepithelial cells that surround the gland alveoli contract and the milk is ejected into
milk ducts from where it can be withdrawn by the suction in the mouth of piglets. The
milk ejection occurs simultaneously in all glands. As the sow does not have teat cisternae,
both the increased intramammary pressure and active pumping by the piglets' jaws and
tongue are necessary for the milk to be extracted. The milk ejection can be recognized
by distinct piglet behavior: as the milk begins to flow, the piglets stop massaging the teat
vicinity with their snout, they hold the teats firmly in their mouth and pull them, thereby
performing rapid sucking jaw movements as they withdraw the milk from the milk ducts.
