Very low surfactant protein C contents in newborn Belgian White and Blue calves with respiratory distress syndrome

We have studied a respiratory dis tress syndrome (RDS) occurring in newborn calves of the Belgian White and Blue (BWB) breed that represents the large majority of beef cattle in Belgium. Pulmonary surfactant isolated from 14 BWB newborn calves that died from RDS and from 7 healthy controls was analy sed for composition and surface activity. An extremely low content or, in s ome instances an absence of surfactant protein C (SP-C) was detected in the RDS samples by Western blotting and differential amino acid analysis [0.03 +/- 0.01 % (w/w) relative to total phospholipids, compared with 0.39 +/- 0 .06 %; For healthy controls (means +/- S.E.M., P < 0.001)]. The contents of surfactant protein B (SP-B) were similar in RDS and control samples. The c rude surfactant samples isolated from RDS calves had higher ratios of total protein to total phospholipid, altered phospholipid profiles and lower SP- A contents. Both crude and organic extracts of RDS surfactant samples showe d increased dynamic surface tension compared with healthy controls when eva luated with a pulsating-bubble surfactometer. The addition of purified SP-C to organic extracts of RDS surfactant samples lowered surface tension. Str ongly decreased levels of mature SP-C associated with fatal RDS and altered surface activity in vitro have, to the best of our knowledge, not been pre viously reported. The mechanisms underlying RDS and the decrease in SP-C in BWB calves remain to be established.