Volume and rate of milk delivery as determinants of swallowing in an infant model animal (Sus scrofia)

The volume transported into the valleculae by the rhythmic tongue movements of suckling is considered the prime factor for initiating pharyngeal swallowing (the movement of milk out of the valleculae and through the pharynx to the esophagus). This study addressed the impact of variation in two factors on sucking (oral phase) and on swallowing (pharyngeal phase) in infant pigs, as a model for mammalian function: (1) the delivery of different-volume aliquots of milk and (2) the delivery of equal-sized aliquots at different frequencies. The number of sucks per second remained constant with change in both aliquot volume and change in the frequency of milk delivery. However, while the number of swallows per second remained constant as delivery volume increased, it increased as delivery frequency increased. Conversely, swallow volume increased with both increase in aliquot volume and in the frequency of delivery. Piglets consequently initiated pharyngeal swallows with a highly variable amount of milk in the valleculae. We conclude that volume is only one factor initiating the pharyngeal swallow. The sensory stimulation of milk delivery to the anterior oral cavity is also a factor in determining the frequency of swallows and the volume of milk per swallow.