Abstract
Simple SummaryArtificial insemination is widely used for pig reproduction. Boar spermatozoa for use in artificial insemination are usually preserved at 17 °C for several days. Storage at lower temperature would be beneficial to reduce the risk of bacterial growth but is hindered by the high chilling sensitivity of boar spermatozoa. Currently, new preservation concepts are evolving which aim to store boar sperm at 5 °C. Before introducing these for animal breeding, sensitive tests are necessary to detect chilling-induced sperm damage. The aim of the study was to examine the potential of two tests systems for detecting sperm injury after chilling in two different semen extenders. It was shown that the analysis of sperm movement patterns and the binding of sperm to oviductal tissue sensitively indicate subtle differences of semen extenders to preserve the quality of chilled spermatozoa. The application of these tests is recommended for testing new hypothermic preservation strategies for boar semen.Sensitive detection of chilling injury in boar spermatozoa is required to evaluate novel hypothermic preservation concepts. The study’s aim was to examine whether analyses of motility patterns and sperm binding in a competitive oviduct explant assay (cOEA) sensitively detect chilling-induced alterations in sperm function. Semen samples (n = seven boars) were split into four subsamples by dilution either in Beltsville Thawing Solution (BTS) or Androstar® Plus and stored at 5 °C or 17 °C. Storage temperature had a significant effect on the distribution of spermatozoa in seven major kinematic clusters. The effect size of chilling at 5 °C as estimated by Cramer’s V was higher (p < 0.05) in the BTS medium (0.21) compared to AndroStar® Plus (0.11). Spermatozoa extended in Androstar® Plus had higher relative binding capacity compared to sperm in BTS (p < 0.05). Binding indices correlated with the percentage of viable, acrosome-intact (r = 0.62) and motile spermatozoa (r = 0.72, both p < 0.001). The cluster size of sperm with slow, vigorous movement was negatively correlated with sperm-oviduct binding (r = −0.43, p < 0.05). In conclusion, the cluster analysis of sperm kinematics and competitive sperm oviduct binding in vitro present meaningful biological tests to assess novel concepts for hypothermic semen preservation.
Highlights
Artificial insemination (AI) is a well-established reproductive biotechnology in pigs worldwide
New concepts for hypothermic preservation of boar semen at 5 ◦ C are evolving to reduce the usage of antibiotics in AI in pigs [1,2]
The aim of the present study was to examine whether chilling boar semen to 5 ◦ C and subsequent storage for 24 h at this temperature in two different extender media affects fertility-relevant sperm traits, i.e., the subpopulation structure in motile spermatozoa with respect to movement patterns and the ability of sperm to bind to oviduct explants in vitro
Summary
Artificial insemination (AI) is a well-established reproductive biotechnology in pigs worldwide. In contrast to other livestock, spermatozoa of boars are highly sensitive to chilling injury and are commonly stored between 15 ◦ C and 18 ◦ C. The relatively high storage temperature bears a risk for bacterial growth which is controlled by adding antibiotics to semen extenders. New concepts for hypothermic preservation of boar semen at 5 ◦ C are evolving to reduce the usage of antibiotics in AI in pigs [1,2]. Assessing chilling injury requires sensitive in vitro assays which test for traits that identify physiological meaningful changes in sperm function. Like other effectors of semen handling, induces cell death in a certain subpopulation of fragile sperm and affects cell function in other cohorts on a sublethal level [3–5]
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