Two treatment protocols for induction of preterm parturition in ewes-Evaluation of the effects on lung maturation and lamb survival

Lambs born prematurely are often unable to breathe due to pulmonary immaturity and a lack of surfactant production. Attempts to deliver live, moderately preterm lambs from critically ill ewes in late pregnancy are therefore often unsuccessful. The objective of this study was to evaluate the potential benefits of repeated administration of dexamethasone (DEXA) to final-stage pregnant ewes on subsequent perinatal lamb survival and respiratory and metabolic disorders associated with neonatal asphyxia. Two different treatment protocols with dexamethasone were used to induce parturition on days 137 and 138 of pregnancy (full term 149 days). In group LTP (long-term protocol, n = 12) low doses of dexamethasone were administered repeatedly starting with 2 mg once daily on days 130-133, followed by a single dose of 4 mg on day 134. For the final induction of parturition 16 mg of the drug were administered on day 135 and this dose was then repeated every 12 h until lambing. In group STP (short-term protocol) 15 ewes received 16 mg DEXA on day 135, followed by the same dose every 12 h until lambing. The vitality and laboratory parameters of the lambs born to these dams were compared to lambs delivered by caesarean section (group CS) on day 147 or 148 of gestation whose dams (n = 23) had received a single injection of 10 mg dexamethasone 12 h prior to surgery, and to lambs born naturally to 19 ewes at full term (group FT) after an average of 149 days of gestation. Lambs from groups LTP and STP were born between day 137 and 139 of gestation, showing characteristics of immaturity. Of 18 lambs in group LTP, 16 survived without critical care (88.9%; 95% confidence interval (CI) = 67.2-96.9%). Group STP comprised 24 lambs, 18 of which survived without critical care (75%; 95% CI = 55.1-88.0%). Out of 39 lambs in group CS, 37 survived (94.9%; 95% confidence interval (CI) = 83.1-98.6%), and 27 of the 28 lambs in group FT, respectively (96.4%; 95% CI = 82.3-99.4%). There was no statistically significant difference in the survival rates between the four groups. In all four groups there was a significant increase of pH, BE and HCO3- values within the first 24h post natum, and a significant decrease in pCO(2(v)) values. Compared to previous studies which indicated high mortality rates in moderately preterm lambs the results indicate that repeated exogenous administration of DEXA has a positive effect on the survival rates of lambs born after induced parturition at around 92% of the full pregnancy term. (C) 2015 Elsevier B.V. All rights reserved.