Postnatal changes in regional blood flow during cold-induced shivering in sow-reared piglets

To determine whether newborn pigs are able to display adequate cardiovascul ar adjustments favouring shivering thermogenesis in skeletal muscles soon a fter birth, regional blood flow and fractional distribution of cardiac outp ut were determined in 1-day-old (n = 6) and 5-day-old (n = 6) conscious pig lets at thermal neutrality and during cold exposure, using coloured microsp heres. Five-day-old piglets stayed with the sow before the experiment. The cold challenge was designed to induce a similar increase (similar to+90%) i n heat production sit both ages. Skeletal muscle blood flow increased with both age (p < 0.05) and cold exposure (p < 0.001), with the effect of cold being more pronounced in 5-day-old piglets than in 1-day-old piglets (+60%, p < 0.05). The difference between individual muscles increased with age, w ith fractional blood flow being 41% higher in rhomboideus than in longissim us thoracis muscle during cold exposure in 5-day-old piglets (p < 0.05). Ca rdiac output was similar at both ages and increased by 23% in the cold (p < 0.001). At 1 day of age, there was no redistribution of cardiac output amo ng the internal organs during the cold challenge, while at 5 days of age, t he increase in muscle fractional blood flow was associated with a reduction (p < 0.05) in the fraction of cardiac output reaching the skin (-24%), the small intestine (-21%), and the liver (-20%). In conclusion, these results suggest that there is a rapid postnatal improvement of cardiovascular adju stments favouring blood perfusion and probably heat production during cold- induced shivering in the most oxidative muscles studied. This cardiovascula r response may play a role in the postnatal enhancement of thermoregulation in piglets.