Sleep is not a prerequisite for the milk ejection reflex in the pig.

Electroencephalographic and electromyographic activities were recorded together with variations in intramammary pressure in unanaesthetized lactating sows during suckling. During each suckling period, milk ejection resulted in a sudden and brief rise in intramammary pressure. From the onset of suckling to the beginning of milk ejection, polygraphic recordings as well as observations of behaviour revealed that the sow was invariably in a state of arousal. This suggests that, unlike what has been proposed for the rat, sleep is not a necessary component of the milk ejection reflex in the pig.