Seminal DNase Activity in Holstein Bull Ejaculates: Effects of Extender and Relationship with Fertility.

Abstract

Previous reports have shown that ejaculates from stallions and bulls exhibit DNase activity. Mechanistically, this activity allows spermatozoa to navigate through extruded neutrophil extracellular traps (NETs), which are composed of DNA produced by polymorphonuclear neutrophils (PMNs). The objective of this study was to identify seminal DNase activity patterns from commercially-extended Holstein bull ejaculates and determine the impact of extender on seminal plasma DNase activity. Furthermore, these DNase activity patterns were compared to known sire conception rates. For the first experiment, Holstein bull ejaculates (n=91) were collected and extended at a commercial bull stud with a mix of glycerol and skim milk. DNase activity of the ejaculates plus extender or extender alone was determined by incubating with DNA for 15 minutes at 37°C followed by gel electrophoresis. Ejaculates were then categorized into one of five profiles based on the DNA degradation pattern in the gels. In a second experiment, neat semen from unknown bulls (n=3) with three replicate ejaculates was serially diluted and DNase activity was determined as described above. The DNase activity of ejaculates from the first experiment was not related to the conception rate data provided by the bull stud. By chance, this data set included 15 sets of paternal half brothers (ranging from 2 to 11 related individuals per set) and 2 pairs of full brothers. DNase profiles were not consistent between half-siblings. One pair of full siblings exhibited the same DNase profile, whereas the second pair of full siblings did not. Extender alone was devoid of intrinsic DNase activity. During the second experiment, extender decreased DNase activity in a dose-dependent manner. Furthermore, the DNase profile of unextended semen did not differ between ejaculates from the same bull. However, different DNase profiles were observed in ejaculates that were extended on different days from the same bull (n=3) due to daily variation in quantities of extender. Taken together, this data indicates that extender use negatively impacts the DNase activity of semen and inter- and intra-bull variation in DNase activity of extended semen is affected by variations in extender volumes.