118 A RAPID, MINIMALLY INVASIVE METHOD OF COLLECTING SEMEN FROM POLAR BEARS

Abstract

Due to reproductive challenges faced by both captive and wild polar bears (Ursus maritimus), there is growing interest in developing assisted reproductive technologies (ART) to overcome infertility and preserve valuable genetics in this species. A polar bear sperm bank is essential in supporting ART endeavors; however, the traditional method of semen collection from wildlife, electro-ejaculation, has been relatively unsuccessful in polar bears. The goal of this study was to evaluate an alternative method of semen collection previously developed for use in cats. Medetomidine, an α2-adrenergic agonist commonly used to anesthetize captive polar bears, has side effects that facilitate semen collection: it stimulates epididymal receptors, causing semen to enter the urethra while concurrently stimulating receptors in the neck of the bladder, preventing urine contamination. The objective of this study was to assess the feasibility of collecting semen via urethral catheterization from male polar bears anesthetized with medetomidine. From 2012–2015, semen collection attempts (n = 9) were performed opportunistically on captive male polar bears (n = 8) in the USA. All males were considered sexually mature, with a mean age of 17.2 years (±2.8). Although all were housed with females, only 2 had sired offspring. Procedures were performed during breeding (n = 7) and nonbreeding seasons (n = 2). Individuals were anesthetized with medetomidine (0.025–0.060 mg kg^–1) in conjunction with tiletamine/zolazepam or ketamine, and anesthesia was maintained using isoflurane. A sterile, lubricated, polypropylene urinary catheter (8 Fr) was inserted ~40 cm at the first 8 procedures and then 80 cm during the final procedure after a necropsy revealed the polar bear urethra is 100 cm in length. Catheters were left in place for 1 min and then retracted slowly while using a syringe to maintain negative pressure. Bears were catheterized 1–3 times during an immobilization. Any fluid recovered in the catheter was then flushed into a sterile tube and sperm motility was assessed microscopically. All values are presented as mean ± standard error of the mean. Semen containing motile spermatozoa was obtained at 8 of 9 (88.9%) procedures. Total semen volume was 509 ± 292 µL, with the highest volume (2500 µL) obtained using the longer (80 cm) catheter. Total sperm count was 2.6 ± 1.6 × 10⁸. Sperm concentration and motility were 6.3 ± 3.7 × 10⁸ mL^–1 and 64.3 ± 9.0%, respectively. Although the percentage of motile sperm and sperm concentration appeared higher during the breeding season, seasonal differences could not be established statistically due to small sample sizes. This study demonstrates that urethral catheterization is an effective method of obtaining semen from polar bears anesthetized with medetomidine, and that longer catheters may be preferable for maximizing sample volume. Although polar bears are seasonal breeders, semen was recovered at both collections during the nonbreeding season, suggesting that spermatogenesis occurs year-round. This minimally invasive procedure is rapid and requires little equipment, rendering it practical for fieldwork.