of in vitro tests to predict fertility of bulls. Can. J. Anim. Sci. 85: 47-52. The overall objective was to develop an in vitro test to predict fertility of bulls in the field. We investigated the bull effect on in vitro embryo production, zona binding and acrosome reaction, and the correlation of this effect to field fertility measured by 60-90 d non-return rate. Frozen semen from three separate ejaculates of eight unrelated young bulls, obtained from an artificial insemination (AI) center, was used. On thawing, ejaculates from each bull were pooled, motile sperm were selected and (a) subjected to immunofluorescent assay at 0 and 4 h of incubation in capacitation medium to assess acrosome status, (b) used in an in vitro fertilization assay system to assess cleavage and blastocyst production rates, and (c) sperm-zona binding assay was carried out to determine the number of sperm bound to the zona pellucida of mature oocytes. Percentage of pre-freeze motile sperm (PrFM) and non-return rate data were obtained from the AI center. PrFM, percentage of acrosome reacted sperm at 0 h (AR1), increase in percentage of acrosome reacted sperm after 4 h (InAR) and sperm-zona binding rates (ZB) differed (P < 0.05) among sperm samples obtained from different young bulls. Significant correlations (P < 0.05) were observed between PrFM and AR1 (r = -0.31), InAR (r = 0.36), and ZB (r = 0.32). AR1 was negatively correlated to ZB (r = -0.27) and cleavage rate (r = -0.20), InAR was positively correlated with ZB (r = 0.31) and cleavage rate (r = 0.26). None of the in vitro tests was correlated with non-return rate. These findings indicate that along with pre-freeze motility, a combination of in vitro tests including the percentage of spontaneously acrosome reacted sperm at thawing, might be useful in predicting bull field fertility. Such a combination of assays, however, has yet to be determined. (r = 0,26). Aucun test in vitro ne présente de corrélation avec le taux de non-retour. Ces constatations indiquent qu'outre la motilité des spermatozoïdes avant congélation, la combinaison de divers tests in vitro, dont le pourcentage de spermatozoïdes dont l'acrosome réagit spontanément à la décongélation pourrait avoir son utilité pour prédire la fécondité des taureaux sur le terrain. Reste à établir la combinaison de tests qui convient à un tel usage.
Mots clés:Fécondité sur le terrain, réaction de l'acrosome, fixation à la zone pellucide, fécondation IV, évaluation de la féconditéArtificial insemination is one of the most successful reproductive technologies developed to improve reproductive efficiency of farm animals, especially dairy cattle. Accurate evaluation of the fertility of bulls used for AI purposes is of utmost importance since a single ejaculate provides several insemination doses and shows much influence on the reproductive potential of a herd (Rodriguez-Martinez and Larsson 1998). Therefore, the basic purpose of semen evaluation procedures is to ensure that only good quality and highly fertile semen is used for AI purposes....