Smithsonian National Zoological Park l Friends of the National Zoo



Collecting Sperm Samples

by Caroline Treadway

It was a frosty fall morning at the Zoo’s Conservation and Research Center (CRC) in Virginia. Scientist Budhan Pukazhenthi, an expert at freezing sperm, and biological technician Jenny Santiestevan were heading to CRC’s Rivinus Barn Complex. Their mission: to collect sperm from a western tufted deer (Elaphodus cephalophus).

At the barn, veterinarian Luis Padilla gently laid an anesthetized tufted deer on the table. Padilla and other vets carefully monitored the deer for vital functions while Pukazhenthi collected semen samples. He quickly examined the samples under a microscope.

Under the microscope, swarms of tufted deer sperm flicked their tails back and forth. Some moved in straight lines; others made circles. Santiestevan tested the semen’s pH and recorded other data. “The sample has 80 percent motility,” he said after 30 seconds or so, referring to the number of sperm moving in the sample. “If they’re moving in a straight line that’s good,” he explained. “A sample with 60 to 70 percent motility is good; 20 to 30 percent is not so good. Especially when freezing, it’s important to maximize the motility of your sample. If you start out with only 20 to 30 percent and then you freeze, you have less to work with after thawing.”

Pukazhenthi and Santiestevan then transported the samples to a laboratory for freezing. There was a flurry of activity. The intern centrifuged samples while Santiestevan counted sperm.
Pukazhenthi mixed the semen samples with several chemicals that facilitate sperm survival during freezing. Next he transferred the samples into clearly marked, skinny, plastic straws. Each contained about a quarter of a cubic centimeter of semen. He then froze them in liquid nitrogen at minus 198° Celsius.

Pukazhenthi’s frozen semen samples will help preserve the genetic diversity of tufted deer. Eighty-eight tufted deer live in North America, mainly in zoos. They all descend from four animals, so inbreeding is a major concern. Typically found in Myanmar, China, and eastern Tibet, western tufted deer are not endangered—yet. But they are fast disappearing within their native range.

“Why only study species when they’re almost gone?” Pukazhenthi said as he worked. “Why wait until we only have 200 left? It is never too early to begin to understand the fundamental reproductive biology of various species around us.”

Smithsonian Zoogoer intern CAROLINE TREADWAY is a graduate journalism student at Boston University.


More: "Frozen Assets"

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Smithsonian Zoogoer 39(1) 2010. Copyright 2010 Friends of the National Zoo. All rights reserved.