Effect of cooling and seminal plasma on the capacitation status of fresh boar sperm as determined using chlortetracycline assay

Insemination of sows with frozen-thawed spermatozoa results in lower fertility, in part due to spermatozoa having undergone a capacitation-like reaction. The present study employed chlortetracycline (CTC) staining analysis to investigate the effect of adding 20% (v/v) boar seminal plasma (SP) to boar spermatozoa on the temporal progress of capacitation and the acrosome reaction in spermatozoa cooled to 5 °C or incubated at 39 °C. Based on CTC staining patterns, seminal plasma appeared to reverse capacitation in spermatozoa that had undergone capacitation while incubated at 39 °C in a capacitation-supporting medium from 59.7 to 36.6% capacitated (P < 0.001). Similarly, the addition of SP to boar spermatozoa cooled to 5 °C resulted in both the prevention of the capacitation-like reaction, and the reversal of an established capacitation-like reaction from 63.3 to 34.2% capacitated (P < 0.001). These observations indicated that some constituent(s) of boar SP both prevent spermatozoa from undergoing capacitation as well as reverse capacitation in spermatozoa that have already undergone the process.