Glycogen depletion according to muscle and fibre types in response to dyadic encounters in pigs (Sus scrofa domesticus)--relationships with plasma epinephrine and aggressive behaviour. 
Changes in glycogen content according to fibre type were assessed in a predominantly white (Longissimus) and a predominantly red (Semispinalis) pig muscle, in response to dyadic encounters involving aggressive interactions.  Tested animals showed significantly lower glycogen levels than the control in the Semispinalis, but not in the Longissimus muscle.  Histological treatment of muscle serial cuts followed by computerized image analysis showed that the observed decrease in muscle Semispinalis glycogen level occurred only in fast-twitch fibres.  Total glycogen and glycogen contents in fast-twitch fibres of the Semispinalis muscle were closely and negatively related to aggressive behaviour, but not with plasma epinephrine levels during and at the end of the encounters.  The present results provide indirect evidences suggesting a major influence of fighting-induced physical activity on muscle glycogen depletion in response to aggressive interactions in pigs.