Piglets vocalize a great deal during the first few days after weaning. The aim of this experiment was to determine if the calls given by piglets vary in response to one factor thought to influence post-weaning adaptation: weaning age. In 22 litters, each containing a minimum of 9 piglets, 3 piglets were weaned under identical conditions at 3, 4 and 5 weeks of age. Vocalizations and weight gain were monitored for the week after weaning. The number of calls produced by piglets of all three ages declined from an average of 8.2 calls/min per piglet on the day of weaning to only 1.6 calls/min 4 days later. Overall, piglets weaned at younger ages called more (P < 0.001): piglets weaned at 3 weeks produced an average of 3.6 calls/min during the week after weaning, while those weaned at 4 and 5 weeks produced 2.9 and 2.3 calls/min respectively. The average frequency of the calls also fell (P < 0.001), from 441 Hz for piglets weaned at 3 weeks of age to 384 Hz for those weaned at 5 weeks. These results suggest that vocalizations can be useful for monitoring post-weaning adaptation in piglets.
Weary, D. M., & Fraser, D. (1997). Vocal response of piglets to weaning: effect of piglet age. Applied Animal Behaviour Science, 54(2-3), 153-160.