Sperm quality in frozen beef and dairy bull semen

Abstract

Background: There is speculation that beef bull semen quality is inferior to that of dairy bulls although few scientific studies are available in the literature. The aim of this study was to evaluate sperm quality in beef bull semen and to determine which parameters could be indicative of fertility after insemination. Sperm quality, assessed by computer assisted sperm motility analysis and flow cytometric evaluation of membrane integrity, levels of reactive oxygen species, mitochondrial membrane potential, acrosome status and DNA fragmentation index, was evaluated in beef and dairy bull semen.

Results: For beef bulls, normal morphology (r = 0.62, P < 0.05) and WOBBLE (r = 0.57, P < 0.05) were significantly correlated with 56-day non-return rate, whereas sperm quality was not significantly correlated with the fertility index score for dairy bulls. Membrane integrity (46 ± 8.0% versus 40 ± 11%, P < 0.05), normal morphology (87 ± 6% versus 76 ± 8%; P < 0.05), and high respiratory activity (52 ± 13 versus 12 ± 4%; P < 0.001) were higher for dairy bulls than for beef bulls. The DNA fragmentation index was lower for dairy bull spermatozoa than beef (3.8 ± 1.1% versus 6.1 ± 2.9%; P < 0.01), whereas some sperm kinematics were higher. Multivariate analysis indicated that type of bull (beef versus dairy) had an impact on sperm quality.

Conclusions: Different assays of sperm quality may be needed for appropriate analysis of beef and dairy bull semen. These finding could be important for cattle breeding stations when evaluating semen quality.

Keywords: Chromatin integrity; Membrane integrity; Mitochondrial membrane potential; Motility; Reactive oxygen species.

Fig. 1

Flow cytometry data: a FSC-SSC pattern obtained as well as the gate used to select spermatozoa for further analysis steps; b shows the regions of analysis used in the acrosome status assay. Lower right: live, reacted, green; Upper right: dead damaged, olive; Lower left: live, non-reacted, grey; Upper left: dead, non-reacted, dark red; c, d results from analysis of mitochondrial membrane status of spermatozoa from a dairy bull and a beef bull, respectively. Indicated are the regions of analysis for spermatozoa with high MMP (orange) and low MMP (green). Events inside the gate for spermatozoa, but outside the regions of analysis, are shown in red

Fig. 2

Relationship between various sperm characteristics and 56-day non-return rate for beef bulls (n = 13). a WOBBLE; b normal morphology; c live superoxide negative; d live hydrogen peroxide negative

Fig. 3

Scatter plot of beef and dairy bulls according to sperm quality (n = 37)

Fig. 4

Partial Least Squares loading plot showing the relationship of breed to the various parameters of sperm quality. Type B and D refer to beef and dairy bulls respectively, Extender A and T refer to Andromed and Triladyl, respectively; morph morphology, living, dead and dying refer to membrane integrity, hyper hypermotility, VCL curvilinear velocity, VSL straight line velocity, VAP velocity of the average path, STR straightness, LIN linearity, WOB wobble, ALH amplitude of lateral head deviation, BCF beat cross frequency; high and low potential: high and low mitochondrial membrane potential; live react, dead react, live not and dead not acrosome status (acrosome reacted or not reacted) in relation to viability, R2 live superoxide negative, R3 live superoxide positive, R4 dead superoxide positive, R5 live hydrogen peroxide negative, R6 live hydrogen peroxide positive, R7 dead hydrogen peroxide negative, R8 dead hydrogen peroxide positive; a or b in connection with R2-R8 refer to non-stimulated and stimulated with menadione, respectively