Auditory brainstem responses in weaning pigs and three ages of sows1

Piglet crushing is a devastating welfare concern on swine farms; however, some sows appear unresponsive to a piglet’s call. Sow hearing ability is rarely considered despite the extensive body of research performed on crushing. In this study, pigs of four age groups (weaning, n = 7; gilts, n = 5; 2nd and 3rd parity, n = 5; 5th parity and up, n = 5) were anesthetized and auditory brainstem responses (ABRs) were performed to measure if pig hearing diminishes with age in a mechanically ventilated barn. Before testing, pigs were placed in a sound dampening box. ABRs were performed on animals using 1,000 clicks at two decibel (dB) levels: 90 and 127 dB sound pressure level. Latencies and amplitudes of waves I–V were measured and interpeak latencies for waves I–III, III–V, and I–V were calculated. Five pigs (three 2nd and 3rd parity, and two 5th parity and above) had no detectable waves at either decibel. Sows in 2nd and 3rd parities had very few distinguishable waves, with only wave I and II present in two sows. Amplitudes of waves I and V increased with increased dB (P < 0.001). Increasing dB decreased the latency of each of the recorded waves (P < 0.01). The vast majority of commercial swine are raised in noisy barn environments; it is possible that these environments directly affect the ability for pigs to hear and normal hearing development in this population of animals. Hearing has a significant effect on swine welfare as hearing is integral to successful animal handing and during moments of animal-to-animal communication. Hearing is a considerable welfare issue on farms and ways to decrease pig hearing loss should be considered.