Preben Christensen

Sperm chromatin structure integrity in liquid stored boar semen and its relationships with field fertility

Extended semen doses from some boars used for AI have been shown to develop high levels of sperm DNA fragmentation during storage. Studies in other animals and humans have shown that if DNA damage is present in a certain percentage of the sperm cells the fertility potential of the semen sample is reduced. The objectives of the present study was to determine the relationship between sperm DNA fragmentation measured using the sperm chromatin structure assay (SCSA) in extended stored semen and field fertility in the boar. Three ejaculates from each of 145 boars were collected. Preparation of the semen doses included dilution with an EDTA extender and storage for up to 72 h post collection. The semen doses were assessed using flow cytometric methods for the percentage of viable sperm (PI/SYBR-14) and sperm DNA fragmentation (SCSA) at 0, 24, 48, and 72 h. A total of 3276 experimental inseminations in Danish breeding herds were conducted. The results showed that for 11 (7.6%) of the boars at least one of the three samples showed a value of DNA fragmentation index (DFI) above 20% within the storage period. Total number of piglets born (litter size) for Hampshire, Landrace and Danish Large White boars was, respectively, 0.5, 0.7 and 0.9 piglets smaller per litter when DFI values were above 2.1% as opposed to below this value. In conclusion the SCSA technique appears to be able to identify individuals with lower fertility with respect to litter size, and could in the future be implemented by the pig industry after a cost-benefit analysis.

In vitro induction of the acrosome reaction in bull sperm and the relationship to field fertility using low-dose inseminations.

The acrosome reaction (AR) is a prerequisite for normal sperm fertilizing capability and can be studied in vitro after induction by various agents. The efficacy of a sperm population to undergo the AR in vivo is expected to influence male fertilizing potential. During the past two decades, a number of attempts have been made to relate the in vitro-induced AR to field fertility in several species. However, to our knowledge, no studies have combined in vitro induction of the AR with the simultaneous detection of sperm viability and acrosomal status using a high-precision flow cytometric technique. Furthermore, large-scale fertility trials using low-dose inseminations are pending. In the current study, the relationship between field fertility and the in vitro-induced AR was investigated using three ejaculates from each of 195 bulls, 156 Holstein and 39 Jersey bulls (Bos taurus), participating in a progeny test program including low-dose inseminations. A range of insemination doses, varying from 2.0 x 10(6) to 15 x 10(6) sperm/dose, was obtained by a controlled dilution process applied to each ejaculate. Different insemination doses were distributed at random among 75,610 experimental first inseminations in 4721 herds and 208 artificial insemination (AI) technicians. Simultaneous detection of sperm viability and acrosomal status was achieved using a triple color flow cytometric technique. Sperm samples from the bulls displayed a wide range of ability to acrosome react in response to calcium ionophore A23187. Both reproducibility of the AR response after induction and relationship between ability to acrosome react and field fertility was highly dependent on the definition of AR inducibility. Six basic and six combined AR indices were assessed. The AR index expressing the fraction of acrosome reacted sperm in the live sperm population after induction by ionophore had the highest repeatability, best described the biological variation in the studied population, and yielded the best significant predictive values on field fertility among the 12 indices considered. Moreover, the ability of sperm to acrosome react appeared to be a noncompensable trait that affects fertility regardless of the number of sperm per insemination dose. The current results therefore indicate that this sperm parameter is important in the field and also may play a role in the IVF laboratory.

Relationship among seminal quality measures and field fertility of young dairy bulls using low-dose inseminations.

Optimal use of genetically superior bulls through artificial insemination (AI) is highly dependent on precise assessment of seminal quality which allows for reasonable estimations of field fertility with normal or low-dose inseminations. In the present study, seminal measures such as sperm motility and morphology, sperm viability, sperm DNA fragmentation, and the ability of the sperm to display an acrosome reaction were tested. The relationships between field fertility and the seminal measures were investigated using 3 ejaculates from each of 195 bulls (156 Holstein and 39 Jersey) participating in a progeny test program. A range of AI doses, varying from 2×10(6) to 15×10(6) sperm/straw, was obtained by a controlled dilution process applied to each ejaculate. The different AI doses were distributed at random among 75,610 experimental first inseminations in 4,721 herds and 208 AI technicians. Most of the seminal measures appeared to contain a predictive value for the nonreturn to estrus at 56 d post-AI (NRR56) regardless of the number of sperm per AI dose and can be regarded as noncompensable sperm traits. But, due to correlations between the individual measures, the best model for describing (and predicting) NRR56 was based on sperm concentration and viability in the neat (raw) semen, and post-thaw sperm viability. The statistical models for describing NRR56 included the following explanatory variables: strength of the estrus, number of sperm per AI dose, breed, parity, and random components representing herds and AI technicians. The present results show that the most precise estimation of a bulls NRR56 can be achieved through flow cytometric detection of sperm concentration and viability in neat semen as well as flow cytometric detection of post-thaw sperm viability.