Vocal behaviour as an indicator of lamb vigour

Abstract

The viability and survival of the neonate lamb relies on its ability to communicate and maintain a strong attachment with its dam. To date there has been little concise information available about the role of the lamb's behaviour, and in particular the importance of acoustic cues, in this relationship as greater attention has been focused on maternal attributes important in facilitating the maternal-young bond. In human and rodent neonates, acoustic features of the distress vocalisation are used as indices of neurological deficit and integrity both at birth and in infant acoustic cry analysis. The aim of this thesis was to investigate potential behavioural indicators of lamb vigour, with a particular focus on vocal behaviour, within the first 12 hours of life. Such measures could provide valuable information for development of reproductive breeding objectives, and provide clarity regarding the role of the lamb in failed maternal-young interactions. Delayed vocalisation initiation in response to a separation stimulus was found to be associated with poor vigour-related behaviour reflecting the capacity of the lamb to reunite and follow the dam over 12 hours postpartum. Vocalisation delay was also associated with risk factors related to poor lamb survival including longer parturition duration, male sex, first parity, heavier birth weight and sire-related conformational attributes likely to result in a more difficult birth. Blood assay markers reflecting fetal distress including poor blood oxygenation, and elevated plasma glucose and lactate levels sampled at birth were also demonstrated to be correlated with vocalisation latency. These associations were concluded to reflect impacts on the lamb's neurological system rather than genetic influences because of evidence provided by within-litter comparisons, and to demonstrate neuroregenerative processes over a 12 hour measurement period. An analysis of lamb distress signals modelled on acoustic cry analysis of the human neonate was also undertaken to compare vocalisation characteristics of lambs with delayed responses to those with rapid responses indicating vigour. Signal features of delayed response lambs were more likely to demonstrate acoustic parameters reflecting glottal instability, lower amplitude and reduced repetition rate. These lambs were more likely to emit inefficient or inappropriate signals in the context of isolation. A significantly higher fundamental frequency, an indicator of pathology in the human infant, was not clearly demonstrated to be associated with compromised lambs in this study. It was also found in a two-choice test, where sheep dams were required to demonstrate a preference for signals of their own co-twins, that ewes preferred acoustic signals of lambs correlated with rapid vocalisation response, higher pitch and greater signal stability. The results indicate that delayed vocalisation responsiveness and other acoustic measures are associated with fetal compromise in the neonate lamb, as shown in the human and rodent models. It was concluded that delayed vocal initiation is a marker for poor postnatal outcome characterised by diminished responsiveness to a distress condition. This research has important implications for understanding failed maternal-young relationships and the consequences for survival in mammalian neonates.