LAYING HEN RESPONSES TO ACUTE HEAT-STRESS AND CARBON-DIOXIDE SUPPLEMENTATION .1. BLOOD-GAS CHANGES AND PLASMA LACTATE ACCUMULATION

Exposure to heat stress lowered partial pressure of arterial blood car bon dioxide (paCO(2)), arterial blood bicarbonate ion (HCO3-), but inc reased arterial blood pH (pHa) and plasma lactate (LA). Increasing amb ient carbon dioxide (CO2) to 1.5% increased paCO(2) from hypocapnic le vels to normocapnic levels, raised HCO3-, lowered pHa and plasma LA to pre-heat stress levels. Following CO2 treatment, respiratory alkalosi s conditions returned. It was evident in this study that increasing am bient chamber CO2 to 1.5% was effective in ameliorating acid-base dist urbances and reducing elevated levels of plasma LA which normally deve lops when laying hens are subjected to an acute heat stress exposure.