Effect of semen dilution to low-sperm number per dose on motility and functionality of cryopreserved bovine spermatozoa using low-density lipoproteins (LDL) extender: Comparison to Triladyl® and Bioxcell®

Artificial insemination with doses containing low-sperm numbers has been utilized to optimize the use of elite bulls. Hen egg yolk is widely used as a cryoprotective agent in semen freezing extender protecting the spermatozoa. Its action is due to the presence of low-density lipoproteins (LDL) in the hen egg yolk. The objectives of the present study were to evaluate the effects of the semen dilution to low-sperm number/dose on sperm motility and integrity of sperm plasma membrane in the cryopreservation process, using two commercial extenders (Triladyl®, Bioxcell®) and LDL extender prepared in our laboratory, 97% purity. Fifteen ejaculates were collected from five fertile crossbred bulls (Bos taurus × Bos indicus). After collection, sperm motility was examined by Computer-Assisted Semen Analysis (Hamilton Thorne), morphological sperm characteristics were evaluated by differential interference microscopy and the integrity of plasma membranes was determined using the hypo-osmotic swelling test. The semen was subsequently divided into three aliquots and diluted with the three extenders into 120 × 106, 60 × 106 and 20 × 106 sperm/mL, corresponding to 30 × 106, 15 × 106 and 5 × 106 sperm/dose, respectively. This study revealed that LDL extender was more effective in preservation of motility and integrity of the plasma membrane of spermatozoa than Bioxcell® and Triladyl® (p < 0.05), but no significant difference was observed between Triladyl® and Bioxcell®. Therefore we can conclude that LDL extender could be used instead of Triladyl® or Bioxcell® at low semen concentration per dose for elite bulls, it also could be envisaged for the industry of sex-stored semen.