Effects of arterial pCO2 on IgG absorption efficiency in neonatal Holstein calves

Absorption of colostral Ig within the first 24 h of life provides the neonate with passive immunity. Delayed first feeding of colostrum, low colostral Ig concentration or compromised metabolic state may reduce the apparent efficiency of Ig absorption (AEA) calculated as the mass of Ig in plasma (g) divided by Ig intake (g). Objectives of this study were to determine if elevated arterial pCO₂ (PaCO₂) in blood reduced AEA in calves and to determine if assisted ventilation of animals with elevated PaCO₂ increased AEA. Holstein calves (n = 48) from primiparous and multiparous dams were separated at birth and blood was collected at 1 h and analyzed for PaCO₂, arterial pO₂ (PaO₂), arterial pH (pHa), arterial actual bicarbonate (HCO₃^-), and base excess. Three treatments were assigned based on PaCO₂ at I h: non respiratory acidosis (NA, n = 19), respiratory acidosis-not ventilated (ANV; n = 17), and respiratory acidosis-ventilated (AV; n = 12). Assisted ventilation was administered via Ambu Bag™ with mask at 1.5 h. Calves received 12 assisted breaths per min for 5 min. Post ventilation blood gas analysis indicated this method reduced PaCO₂. Mean I h PaCO₂ for calves on NA, ANV and AV treatments were 45.52, 53.04, and 53.22 (SE = 0.71) mm of Hg, respectively. Blood was sampled by jugular venipuncture at I, 13, 25, 37, and 49 h for analysis of plasma IgG by single radial immunodiffusion. Evans' blue dye (1.5 ml) was injected into the jugular vein for estimation of plasma volume and AEA. Treatment had no effect on AEA at 25 h, plasma IgG at 13,25 or 37 h or plasma volume at 25 h (P > 0.10). Mean AEA, plasma IgG and plasma volume at 25 h of age were 26% (SE = 1.5), 11.73 g/L (SE = 0.50) and 3 .422 L (SE = 0.001), respectively. Regression of AEA and plasma IgG on PaCO₂ at 1 h indicated no effect of 1 h PaCO₂ on IgG absorption. Results from this study indicate that acquisition of passive immunity was not inhibited by elevated PaCO₂ at 1 h.