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.