Effect of sperm concentration on boar spermatozoa mitochondrial membrane potential and motility in semen stored at 17 °C

The aim of the study was to assess the effect of sperm concentration in the ejaculate on the mitochondrial membrane potential and motility of Landrace boar spermatozoa during storage of diluted semen at 17 °C. The study was conducted on ejaculates collected from 10 boars aged 1.5–2 years. Based on sperm concentration measurements, two groups of boars were identified: Group 1 – boars providing ejaculates with a sperm concentration of at least 500 × 103/mm3 and Group 2 – boars providing ejaculates with a sperm concentration of less than 500 × 103/mm3. Four ejaculates were collected manually from each boar. Each ejaculate was diluted with Biosolvens Plus diluent, and insemination doses were prepared and stored at 17 °C. Mitochondrial membrane potential and motility of spermatozoa were evaluated at each insemination dose. The tests were carried out after 1, 24, 48, 96 and 168 h of storage. Based on the results, it was found that ejaculates with a sperm concentration ≥ 500 × 103/mm3 have a lower share of spermatozoa with high mitochondrial membrane potential than ejaculates with a sperm concentration below 500 × 103/mm3. A high correlation between the share of spermatozoa with a high mitochondrial membrane potential and motility of spermatozoa was demonstrated in the first 24 h and after 96 h of semen storage, which was confirmed by the calculated phenotypic correlation coefficients. Sperm cells in ejaculates with a higher sperm concentration are more sensitive to storage time than spermatozoa in ejaculates with a lower concentration. Ejaculate, pigs, semen quality Insemination of pigs plays an important role in the reproduction of this animal species. It is the most common method of breeding pigs in the world that allows increasing the genetic progress of the swine population. Boars used in insemination are usually characterized by good production-related predisposition, as well as high breeding value. High variability observed in the physical characteristics of ejaculates, which affects the economics of using a given individual is a fairly serious problem faced by sow insemination stations. The source of this variation can be the boar breed (Schulze et al. 2014; Yeste 2016; Wysokińska and Kondracki 2019), age (Banaszewska et al. 2015), and environmental factors (Zasiadczyk et al. 2015; Kowalewski et al. 2016). Individual variation is also important in reproduction. This variability affects the male’s predisposition for insemination use as males provide semen with different physical characteristics of the ejaculate. The ejaculate volume, sperm concentration and sperm motility are determined immediately after collection. Based on these indices, the number of insemination doses that can be obtained from the ejaculate is determined, and this determines the economic efficiency of using the individual in insemination. Some studies have shown the effect of sperm concentration on head dimensions and sperm morphology (Kondracki et al. 2011; Kondracki et al. 2013). It is possible that sperm cell concentration may also affect the potential of the spermatozoon mitochondrial membrane. Maintenance of normal mitochondrial membrane potential is necessary for mitochondria to produce adenosine triphosphate (ATP) (Luo et al. 2013). Mitochondria are thought to be important organelles that can be used to assess semen quality. Due to the fact that mitochondria contain their own DNA and membrane potential, they are easy to study (Amaral and Ramalho-Santos 2010). Disorders present ACTA VET. BRNO 2020, 89: 333–340; https://doi.org/10.2754/avb202089040333 Address for correspondence: Siedlce University of Natural Sciences and Humanities Prusa 14 Str, 08-110 Siedlce, Poland Phone: +48 25 6431388 E-mail: anna.wysokinska@uph.edu. pl http://actavet.vfu. cz/