Ontogenetic Changes in Mammalian Feeding: Insights from Electromyographic Data

All infant mammals make a transition from suckling milk to eating solid foods. Yet, the neuromuscular implications of the transition from a liquid-only diet to solid foods are unknown even though the transport and swallowing of liquids is different from that of solids. We used legacy electromyography (EMG) data to test hypotheses concerning the changes in motor pattern and neuromuscular control that occur during the transition from an all-liquid diet to consumption of solid food in a porcine model. EMG signals were recorded from five oropharyngeal muscles in pigs at three developmental stages (infants, juveniles, and adults) feeding on milk, on food of an intermediate consistency (porridge), and on dry chow (juveniles and adults only). We measured cycle frequency and its variation in "transport cycles" and "swallow cycles". In the swallow cycles, a measure of variation of the EMG signal was also calculated. Variation in cycle frequency for transport and swallow cycles was lowest in adults, as predicted, suggesting that maturation of feeding mechanisms occurs as animals reach adulthood. Infants had lower variation in transport cycle frequency than did juveniles drinking milk, which may be due to the greater efficiency of the infant's tight oral seal against the teat during suckling, compared to a juvenile drinking from a bowl where a tight seal is not possible. Within juveniles, variation in both transport and swallow cycle frequencies was directly related to food consistency, with the highest variation occurring when drinking milk and the lowest when feeding on solid food. There was no difference in the variation of the EMG activity between intact infants and juveniles swallowing milk, although when the latter swallow porridge the EMG signals were less variable than for milk. These results suggest that consistency of food is a highly significant determinant of the variation in motor pattern, particularly in newly weaned animals.