NEONATAL DEVELOPMENT OF THE DIAPHRAGM OF THE HORSE, EQUUS-CABALLUS

The diaphragm of neonatal horses is significantly different from the d iaphragm of adult horses in terms of histochemical fiber type composit ion, myosin heavy chain isoform, and native myosin isoform composition . There is a significant increase in the percentage of type I fibers p resent in the diaphragm with increasing age from birth through about s even months postnatal age. A possible lack of postural tone in the hia tal region of the neonatal diaphragm is suggested to account for incre ased incidence of vomiting or aspiration pneumonia in younger horses. The isoform data lead to rejection of the hypothesis that the diaphrag m of the horse should, as an ungulate, be relatively precocial in its rate of maturation relative to other non-ungulate mammals that have be en studied. (C) 1994 Wiley-Liss, Inc.