Influence of Blood Serum from Bulls and Heifers on Head-to-Head Agglutination and Acrosomal Maintenance in Bovine Spermatozoa1

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Abstract
Three ejaculates from each of 3 bulls were used in a split ejaculate design to determine the influence of pre-freeze and post-thaw addition of either bull or heifer serum on the percentage of head-to-head agglutination (HHA), intact acrosomes (PIA) and motility (MOT) of spermatozoa. Within the type of serum added, there was no difference in HHA between pre-freeze and post-thaw serum additions at 0 h. Higher (P < 0.01) HHA was present at 4 and 8 h when serum was added after thawing. Heifer serum resulted in greater (P < 0.01) HHA than did bull serum at all hours of evaluation regardless of the time of serum addition. The HHA observed with heifer serum involved the acrosomal region predominantly while bull serum involved the acrosomal and post-nuclear cap regions. Heifer serum also caused spermatozoa to agglutinate in much larger groups than bull serum. There was no consistent difference in PIA between bull and heifer serum. Neither the time of serum addition nor the type of serum influenced motility. When heifer serum was added to spermatozoa, the overall r between HHA and PIA was 0.82 (P < 0.01). HHA was not related to PIA when bull serum was added. Different mechanisms for HHA may be involved when bovine spermatozoa are exposed to bull or heifer serum.