It is described certain qualitative seminal characteristics and the fertility of a Thoroughbred stallion, during five consecutive breeding seasons (1990 a 1994). High percentages (13.6 a 39%) of abnormal acrossomes were observed in the ejaculates (N° = 15), being the majority of the "Knobbed Acrosome Defect" type (dark staining area or eccentric thickening at the apex of affected spermatozoa). The pregnancy rate (P) varied between 25 e 90% and the per cycle pregnancy (P/C) between 20 e 59%. Regression analysis showed that P/C was significantly (p<0.05) related to the percentage of abnormal acrossomes (R²=0.87). Other seminal characteristics considered in this report were not associated (P>0.05) to fertility indexes. The conclusion is that the acrossomal defect, in the present case, could be attributed to arrested spermiogenesis. Such abnormality significantly affected stallion fertility.
stallion; acrossome; semen; fertility
