Auditory brainstem response in sheep. Part II: Postnatal development.

The auditory brainstem response (ABR) was recorded from 15 chronically instrumented lambs between birth and 7 weeks of age as well as from four adult ewes. Latency changes observed within two days of birth may be related to the dissipation of fluid from the lamb external auditory canal and middle ear cavity. Developmental changes observed in the lambs included an early period of wave latency decrements from 1 to 4 weeks followed by a subsequent increase in wave latencies from 4 to 7 weeks. These changes were significant for the I-IV interwave interval, possibly reflecting the combined effects of increased myelinization and increased neural track length. Responses from 7 week-old lambs were not significantly different from those obtained from the ewes.