Relationship between the proportion of capacitated spermatozoa present in frozen-thawed bull semen and fertility with artificial insemination

The objective of the present study was to confirm the presence of premature ly capacitated spermatozoa in frozen-thawed bull semen and to investigate t he relationship of premature capacitation to the fertility of the respectiv e semen. Twenty batches of frozen semen from young Al bulls of the Swedish Red and White breed with known fertility (expressed as 56-day non-return ra tes; 56 d-NRR) were tested using a Chlortetracycline (CTC) assay to assess capacitation status in frozen-thawed spermatozoa. The status of capacitatio n, as evidenced in this experiment, was further tested based on the hypothe sis that capacitated spermatozoa present in frozen-thawed semen should unde rgo the acrosome reaction JAR) on co-incubation with homologous zona pelluc ida (ZP) glycoproteins. The percentages (mean +/- SEM) of uncapacitated, ca pacitated and acrosome-reacted spermatozoa in the frozen-thawed semen (n = 20) were 49.3 +/- 11.9, 36.3 +/- 8.3 and 14.2 +/- 11.9, respectively. On co -incubation with ZP, there was a significant increase (p = 0.001) in the pr oportion of spermatozoa undergoing the AR compared to the control with a co ncurrent decrease in the proportion of capacitated spermatozoa, suggesting that a proportion of capacitated spermatozoa were undergoing the AR. The pr oportion of viable, uncapacitated spermatozoa present in the frozen-thawed semen was correlated to the 56 d-NRR (n = 20, r = 0.5, p = 0.03). In conclu sion, a proportion of spermatozoa in frozen-thawed semen was capacitated an d the proportion of viable, uncapacitated spermatozoa present in semen was positively correlated to fertility.