Discrete subpopulations of motile sperm cells have been found for several species and are implicated to be important for sperm functionality. The aim of this present study was to examine the motile subpopulations in swim-up-selected bull spermatozoa and the relationship between subpopulations in fresh and frozen–thawed sperm cells. In experiment 1, swim-up (SWUP)-selected and non-selected (control) sperm cells were analyzed using a Computer-Assisted Sperm Analyzer (CASA). In experiment 2, the semen from nine bulls was cryopreserved and analyzed using CASA both before and after freezing and after incubation at physiological temperatures. The SWUP population had a higher proportion of total motility, progressivity, and velocity compared to the control (p < 0.05). Likewise, both incubation over time and cryopreservation affected motility and motility parameters (p < 0.05). The population of rapid progressive (RapidP) sperm cells dominated the SWUP fraction and was higher than in the control samples (p < 0.05). Furthermore, RapidP was also the main part of fresh semen, but decreased significantly over time during incubation and due to cryopreservation. In conclusion, RapidP was the main population in SWUP-selected spermatozoa and seems to be an important subpopulation contributing to the differences between treatments and in response to the freezing of sperm cells.

Metabolomic analysis of boar semen associated with sexual maturation is essential for improving fertility management and breeding, with amino acids and amines playing key roles in the reproductive process. This study aimed to explore changes in amino acids and amines in boar spermatozoa and seminal plasma during puberty to sexual maturity and identify potential biomarkers of sexual maturity. Semen was collected from the same 15 Duroc boars over time at approximately 7 months (Age 1), 8.5 months (Age 2), and 10 months (Age 3). Liquid chromatography-mass spectrometry was used to analyse amino acids and amines in spermatozoa and seminal plasma separately. Multivariate analysis (PLS-DA) revealed pronounced age-dependent changes in amino acids and amines in spermatozoa between Age 1 and Age 3, and more subtle shifts in seminal plasma. Univariate analysis (Repeated measure ANOVA/Friedman) revealed that glutamate and taurine had significant pairwise differences in seminal plasma (P < 0.05). In sperm, 15 amino acids (glutamate, alanine, aspartate, choline, taurine, histidine, methionine, tryptophan, leucine, cystine, tyrosine, arginine, lysine, valine and glycine) exhibited significant pairwise differences (P < 0.05). VIP scoring (>1.5) prioritised glutamate, alanine, aspartate, and choline as key contributors to the variations and pathway analysis implicated alanine, aspartate and glutamate metabolism, and histidine metabolism linked to sexual maturity. Our study highlights metabolic changes during sexual maturation, identifying potential biomarkers for assessing reproductive maturity. These findings are initial steps toward optimising younger boars' usage in breeding, enhancing genetic gain, and reducing costs associated with their non-productive days at AI centres.

Background: Oestrous synchronisation of cattle has been widely applied to accomplish simultaneous ovulation in animals and facilitate timed artificial insemination. The main aim of this study was to investigate the ovarian follicular growth and ovulatory response to oestrus and ovulation synchronisation in Norwegian Red heifers and cows. Oestrous cycles in 34 heifers and 10 cows from 4 herds were synchronised with two PGF_2α analogue treatments 11 days apart, followed by GnRH analogue treatment for induction of ovulation. Thereafter, the ovaries were examined by ultrasonography at 3 h intervals until ovulation. Results: The luteolytic effect of the PGF_2α analogue was verified in 9 of 10 cows by progesterone contents in milk. Maximum physical activity of the cows occurred on average 69 h after PGF_2α analogue treatment. An ovulatory response was recorded in 95.5% (42/44) of the animals. A significant difference in follicle size at ovulation was found between 2 of the herds. Animals with medium sized and large follicles and heifers aged > 16 months ovulated earlier than other animals. Conclusions: The applied sequence of treatments in the study was shown to be effective in synchronizing and inducing ovulation within a relatively narrow time interval in the Norwegian Red heifers and cows, consistent with findings in other cattle breeds.