The behavioural and physiological effects of prolonged exposure to a startling acoustical stimulus observed in the broiler chicken Gallus domesticus (L.)

In response to suggestions made in the poultry industry that acoustical startle could promote permanent behavioural and physiological aberrations and, perhaps, even death in broiler chickens, a study was initiated in which broilers were subjected to varying regimes of acoustical stimulation throughout their eight weeks of life. The stimulus employed during this research consisted of recorded human voices played at 90 db for thirty- second periods. During stimulation all behaviour exhibited by the birds was recorded and ranked according to previously defined scale, position along this scale being determined by response severity. The heart rate response to the acoustical stimulus was monitored using miniature transmitters, implanted in the abdominal cavities of the birds when these had reached four weeks of age. Heart rate was monitored both during stimulation and non- stimulation periods. All mortality was noted and classified as to probable causative agent. Feed consumption was monitored throughout the eight-week growing period. Body weight was measured on the fifty-sixth day of life, and the resulting data were then used with the feed consumption statistics to determine the feed conversion indices for each experimental condition. Using all of these parameters, groups receiving different amounts of stimulation were compared to establish whether any behavioural or physiological aberrations occurred which could be attributed to the effects of acoustical stimulation and, if so, whether these aberrations were permanent or temporary in nature and whether they were aggravated or moderated by continued exposure to the startling stimulus. Results from all tests indicated that prolonged exposure to a startling acoustical stimulus caused no permanent changes either in behaviour or in the selected physiological parameters studied during the course of this research. All responses, both behavioural and physiological, were purely temporary in nature and, furthermore, were subject to significant moderation through the tempering influence of habituation. No evidence was found which suggested that any regime of acoustical stimulation could or did promote increases in mortality.