Bronchoalveolar lavage in the newborn foal.

Two bronchoalveolar lavages, 24 h apart, were performed on 15 foals, ranging in age from 1 to 21 days. In the first lavage, a numerical deficiency in alveolar macrophages was demonstrated in foals up to 2 weeks of age when compared with older (2-3 years of age) horses. Alveolar macrophages obtained from the lungs of 2-3-day-old foals also demonstrated significant impaired chemotactic function. In the second lavage, although an increase of alveolar macrophages was noted, a dramatic increase of polymorphonuclear neutrophil (PMN) mobilization occurred in the foals, thus providing a phagocytic back-up for the alveolar macrophage host defence mechanism. In contrast, PMN response to lower respiratory tract perturbation in older horses was negligible. The results of this study suggest that the numerical and chemotactic deficiency found in alveolar macrophages of the neonate may play a role in the foal's susceptibility to respiratory disease.