The Influence of Air Contact on the Quality of Extended Boar Semen

Abstract

Background: The extensive use of artificial insemination in the swine industry emphasizes the need for distribution of good quality semen doses by the artificial insemination centers. A factor that could modify seminal quality is the contact of extended semen with environmental air. However, only few studies have investigated the effects of air presence on semen parameters. Thus, the aim of the present study was to evaluate the influence of different amounts of air on porcine semen quality during the storage period. Materials, Methods & Results: Four ejaculates from five sexually mature boars were used. Each ejaculate (n = 20) was isothermically diluted (30 x 106/mL) in a BTS-extender and assigned to three groups differing on the amount of air entrapped within the polystyrene tubes (100 mL). In group AIR-0 the tubes were completely filled with extended semen (0% air); in group AIR-25, 75% of the tube volume was filled with extended semen and 25% with air; in group AIR-50, 50% of the tube volume was filled with extended semen. The semen doses were stored at 17.3 ± 0.5ºC for 120 h. The motility parameters were assessed at 24, 72 and 120 h of storage using a CASA system. The evaluation of acrosomal integrity was performed by examining formalin-fixed samples under phase-contrast microscopy (1000 x) at 72 and 120 h of storage. The pH was measured at 24, 48, 72, and 120 h of storage with a digital pH-meter. At 120 h, samples were incubated in waterbath at 38°C for the thermoresistance test and sperm motility was assessed after 30 and 120 min of incubation. For each time analysis, a different sealed tube was used in order to maintain a constant amount of air within the tubes during storage Data were analyzed as repeated measures using the GLIMMIX procedure of SAS® Software. Boar and week of collection were included as random effect in the model. Groups were compared using the Tukey-Kramer test at a significance level of 5%. The pH was significantly influenced by the amount of air entrapped within the tubes (P < 0.01). Throughout the experiment, the pH of semen doses was higher as the amount of air increased within the tubes. The mean pH for groups AIR-50, AIR-25 and AIR-0 was 7.51 ± 0.06, 7.25 ± 0.06 and 7.07 ± 0.06, respectively. Overall motility was similar among the groups for up to 24 h of storage. At 72 h and 120 h of storage, total, progressive and rapid motility were higher (P < 0.05) in AIR-0 compared to AIR-50. The kinematic parameters DAP and VAP decreased as the volume of air within the tubes increased (P < 0.05). Group AIR-0 exhibited higher values (P < 0.05) for DSL, DCL, VSL, VCL, BCF, and WOB compared to AIR-25 and AIR-50. Furthermore, after the thermoresistance test performed at 120 h of storage, total motility, progressive motility and rapid motility were negatively affected (P < 0.05) by the increasing amounts of air within the tubes. There was no effect of air amount within the semen doses on acrosome integrity (P > 0.05). Discussion: The presence of air within tubes affects the quality of extended semen during storage, resulting in increase of pH and subsequent decrease in motility preservation. This pH-rise could be explained by the loss of CO2 from the diluted semen to the air compartment within the tube. At the same time, it is possible to infer that this event influences the intracellular pH of the spermatozoa, increasing sperm metabolism and, consequently, impairing sperm motility. Therefore, we conclude that avoiding air presence within storage containers is recommended in order to ensure the quality of boar semen doses.