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Thirty-five calves were delivered by caesarean section near to term. During the operation amniotic fluid was collected for determination of the lecithin/sphingomyelin (L/S) ratio. Clinical examination of the calves and analysis of blood gas concentration (venous blood) were carried out within the first hour of life. Fifteen out of 35 calves under examination did not show clinical or blood gas disorders in the course of the first hour of life. In these calves, the L/S ratio, which represents a measure for the maturity of the surfactant system, averaged 2.6. The other 20 calves, however, developed a respiratory distress syndrome together with a progressive respiratory and metabolic acidosis within the first hour of life. The L/S ratio in the animals affected with respiratory distress syndrome reached an average value of 1.5 which was significantly below that of the calves not suffering from respiratory distress. Eleven of the 20 calves which developed respiratory distress syndrome died within the first 60 hours of life. The most striking findings in the post mortem examinations of these animals were intracranial haemorrhages and pulmonary lesions (hyaline membranes, interstitial and alveolar oedema). On the basis of the significantly lower L/S ratio and the post mortem findings, it is to be assumed that the respiratory distress syndrome in calves, equally with that in infants, is attributable to a surfactant deficiency.

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Postpartum adrenocortical responses to adrenocorticotropic hormone in cows after normal (n = 10) and difficult (n = 52) parturition were investigated. The post-partum adrenocortical function of cows was affected by type of parturition (spontaneous parturition, forced extraction of fetus, caesarean section calving with or without attempted forced extraction, and total fetotomy) and day after calving (d 1, 4, and 8; d 0 = day of parturition). Cows after normal calving did not show enhanced or depressed adrenocortical function postpartum. Adrenocortical function was enhanced, compared with cows calving normally, for cows with dystocia that had a caesarean section after forced extraction was attempted and in cows in which calves were already dead and total fetotomy was performed. Cows with dystocia assisted with forced extraction by one to two people and cows that had caesarean sections without forced extraction did not show higher plasma glucocorticoid concentrations before or after adrenocorticotropic hormone administration than did cows with normal calving. Results indicate that dystocia requiring caesarean section following unsuccessful extraction or total fetotomy enhanced postpartum adrenocortical function in cows.

Plasma concentrations of beta-endorphin and met-enkephalin were measured, with appropriate radioimmunoassays, in cows during gestation and at parturition and in newborn calves. During pregnancy beta-endorphin immunoreactivity (IR) concentration increased, but values during the last month of gestation were not different from those at parturition. Highest met-enkephalin IR levels were obtained in cows during calving. A term Caesarean section caused an increase in plasma beta-endorphin and met-enkephalin IR concentrations, but no such increase occurred in cases of a preterm Caesarean section. In calves beta-endorphin IR values were lower before umbilical cord rupture than immediately after birth. Values decreased continuously thereafter. This was also the case for met-enkephalin IR concentrations in calves born at term. In preterm calves met-enkephalin IR values were low immediately after delivery and increased during the first hour of life. A significant correlation existed between the degree of acidosis and plasma levels of both opioid peptides in the calves. We conclude that a direct stimulation of peripheral beta-endorphin release by the pain or stress associated with calving does not seem to exist in cattle, whereas met-enkephalin seems to be more directly related to parturition. In calves the change to the extrauterine environment causes an immediate, increased release of both opioids.