The percentage of spermatozoa lost during the centrifugation of brown bear (Ursus arctos) ejaculates is associated with some spermatozoa quality and seminal plasma characteristics

Abstract

Cryopreservation of brown bear (Ursus arctos) semen requires centrifugation to increase concentration and/or remove urine contamination. However, a percentage of the spermatozoa are lost in the process. This percentage varies considerably between males and ejaculates, and we have studied the effect of sperm quality and seminal plasma characteristics on the spermatozoa recovery rate after centrifugation. One hundred and thirty one sperm samples obtained from fifteen brown bear males by electroejaculation under general anaesthesia were used. The ejaculates were centrifuged 600 × g for 6 min. Motility was assessed by CASA, and acrosomal status (PNA-FITC) and viability (SYBR-14/propidium iodide) were determined by flow cytometry. Seminal plasma characteristics (albumin, alkaline phosphatase, calcium, cholesterol, creatine, glucose, glutamic oxaloacetic transaminase (GOT), lactate, lipase, magnesium, phosphate and total protein) were determined by a biochemical and gas analysis. Total motility (r = 0.26; P = 0.005) and cell viability (r = 0.20; P = 0.033) were positively correlated with the percentage of recovered spermatozoa. Sperm recovery was correlated with the concentration of several components of seminal plasma: negatively with glucose concentration (r = −0.47; P = 0.005) and positively with the enzymes GOT (r = 0.36; P = 0.040) and lactate dehydrogenase (r = 0.36; P = 0.041). After sorting the data into classes according to sperm recovery (Low: 0–39, Medium: 40–69, High: 70–100), we observed that the samples with a lower recovery rate derived from ejaculates with lower values for TM, VAP and viability (P < 0.05). Multiple regression analysis rendered two models to define the post-centrifugation spermatozoa recovery which included total motility and damaged acrosome or glucose, GOT and lactate dehydrogenase. We discuss these relationships and their implications in the electroejaculation procedure and the handling of the sample during centrifugation.