The pathogenesis of dystocia and fetal malformation in the horse.

From a total of 601 severe dystocias in mares, 408 (68%) of the fetuses were in anterior, 95 (16%) in posterior and 98 (16%) in transverse presentation, compared with 99%, 1% and 0.1% respectively for spontaneous parturitions. From the cases with anterior presentation, 151 (37%) showed reflected heads and necks. From the cases with posterior presentation, 47 (50%) presented hip flexions, 25% had hock flexions, and 25% had stretched hind legs, 45 (47%) of the fetuses were in lateral or ventral position, and 28 (30%) of the fetuses were malformed (mainly torticollis and head scoliosis). All 98 cases of transverse presentation were complete or partial bicornual gestations; 34 (35%) fetuses were malformed (mainly wryneck). The best adapted obstetrical method and the results obtained for dam and fetus by means of reposition, embryotomy and Caesarian section are considered. It is concluded that, in mares, posterior and transverse presentations are important causes of fetal malformation and of dystocia.