Background – Studies in both humans and rodents have shown an endogenous entrainment of 24 h rhythms in plasma glucose and insulin metabolism (1). These rhythms are regulated by the suprachiasmatic nucleus and are independent of the influence of feeding activity (1). Little is known of these metabolic rhythms in the domestic pig despite the fact that pigs housed in commercial environments are maintained at ambient photoperiod.
Objectives – To determine 24 h profiles in insulin, glucose and feeding behaviour in pigs fed ad libitum and entrained to a 12 h (0600 to 1800 h) light regimen.
Design – Ten entire male pigs were allocated randomly to individual pens in the same room maintained at 22.0 ± 0.7oC. Jugular cannulae were introduced into each pig via the ear vein 24 h prior to the onset of sampling. Blood samples (3mL) were taken at intervals of one hour for 24 h and the plasma stored at -20°C until assayed. Circulating insulin concentrations were determined by radioimmunoassay and plasma glucose concentrations by enzymic analysis. Feeding behaviour was monitored by video analysis over the sampling period.
Outcomes – Feeding behaviour was characterized by a distinct photoperiod entrainment with activity greater during the period of light compared to the period of darkness. Both glucose and insulin concentrations displayed an ultradian rhythm although plasma insulin secretion was correlated to neither feeding behaviour nor glucose status. Conclusions – The data suggest that pigs consume food at regular intervals throughout the daylight hours. Feeding animals ad libitum may not be metabolically efficient as insulin secretion is not correlated with feeding behaviour. Reference
1 la Fleur, SE. Daily rhythms in glucose metabolism: suprachiasmatic nucleus output to peripheral tissue. J Neuroendocrinol 2003; 15: 315-322.