Influence of Homologous Blood Serum on Motility and Head-to-Head Agglutination in Nonmotile Ejaculated Bovine Spermatozoa1

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Abstract
Twenty-five ejaculates, five from each of five different bulls, were used to determine the influence of heat-treated heifer serum on motility, head-to-head agglutination, and acrosomal integrity in aged nonmotile spermatozoa. Spermatozoa from each ejaculate were diluted immediately after collection to 30 x 106 spermatozoa/ml in 2.9% sodium citrate and incubated for 8 h at 37°C. As a result of this 8 h incubation, spermatozoal motility was lost and loss of acrosomal integrity was minimal. Immediately following the 8 h incubation, 20% (v/v) homologous heifer serum was added to each sample which was again incubated at 37°C for 8 h. Aliquots were evaluated at 1 min, 2, 4, 6, and 8 h for percentage motile spermatozoa (% MOT), percentage intact acrosomes (PIA), and percentage head-to-head agglutination (HHA). The addition of serum resulted in an immediate (1 min) increase (P<0.01) in progressive motility for all 25 ejaculates. All but two ejaculates responded to the addition of serum with motility equal to or exceeding the motility estimate made immediately after collection of the semen. These 23 ejaculates remained motile throughout the 8 h incubation in serum. No correlation was found between the postcollection motility estimate in 2.9% sodium citrate and motility immediately (1 min) following addition of serum. Ejaculates with low postcollection motility responded to the serum treatment as well or better than ejaculates with high postcollection motility. Significant (P<0.01) HHA occurred in all ejaculates following the addition of serum. Although % MOT was maximal 1 min following addition of serum, maximum HHA was not observed until 2 h after serum addition. There was a decline (P<0.01) in PIA and HHA during the 8 h postserum incubation; however, acrosomal integrity was higher than HHA at each evaluation time. Once HHA had reached its maximum, an overall positive correlation (r = 0.73, P<0.01) was found between HHA and PIA for the 2, 4, 6, and 8 h evaluation times.