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Title: Stress-induced oviposition delays in laying hens and their physiological causation
Author: Reynard, Martin
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1996
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A variety of stressors cause hens to delay oviposition and this can result in characteristic eggshell abnormalities which are commercially undesirable. This project examined the duration of stress-induced oviposition delays in medium-hybrid hens and investigated their underlying physiological causation. Social stress (relocation of hens from individual to group cages) was used to induce the oviposition delays. From behavioural observations of stress-induced oviposition delays, it was found that eggs were laid either before a threshold of approximately 3 h delay or after at least 7 h delay. This distinction between short- and long-term delays accounts for different types of eggshell abnormality. As oviposition is associated with ovulation of the subsequent egg, it was important to establish whether stress-induced oviposition delays were a consequence of ovulation delays. From investigations of the stage of formation and position of the subsequent egg in the oviduct, it was concluded that stress can cause short delays in ovulation but this is not associated with all oviposition delays. Oviposition is caused by uterine contractions induced by release into the circulation of ovarian prostaglandins and neurohypophysial arginine vasotocin (AVT). Two possible physiological mechanisms which may account for the stress-induced oviposition delays were examined. First, opioid peptides released in response to stress may inhibit AVT release. Second, adrenaline released in response to stress may directly suppress uterine contractions. Plasma AVT concentration was elevated at the time of delayed oviposition, but not during the delay, and AVT injection rapidly ended delays, thus supporting the hypothesis that delays are caused by inhibition of AVT release. The possible role of opioid release in causation of stress-induced oviposition delays was investigated by treating hens with appropriate receptor antagonist and agonist compounds.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available