JERUSALEM — The founder of the Tel Aviv-based specialty firm raves about his product with the same gusto distillers reserve for their top-notch scotch. He’s particularly proud of his “premium” line. Sure, it costs a bit more, but it’s targeted at a more discriminating client.

Dr. Jacob Ronen is in the sperm business. Among other things, as head of Cryobank Israel, the country’s largest private sperm bank, he guarantees that his stable of superior donors includes only tall, twentysomething ex-soldiers whose sperm has passed rigorous genetic testing.

But finding such super sperm isn’t as easy as it used to be. Only 1 in 100 donors makes the cut. A decade ago, it was 1 in 10.

And it’s not just first-rate sperm that’s in short supply. All of Israel’s half a dozen or so sperm banks are scrambling to keep their liquid-nitrogen freezers stocked.

Simply put, the quality of Israeli sperm is falling at an alarming rate, and no one’s sure exactly why.

Fertility is a major issue in Israel, where memories of the Holocaust genocide are fresh, and having children is an entrenched part of Judaism. There’s also a political aspect, because birthrates among Arabs in Israel have at times been as much as double those of Jews, triggering a population race that some believe could one day affect who controls the land.

So the drop in the quality of sperm is raising some red flags, even though the cause remains a mystery. Speculative theories range from the mundane (carrying cellphones in front pockets) to the far-fetched (depleted uranium from exploded munitions). Some Israeli scientists are looking seriously at naturally occurring hormones, particularly estrogen, in Israel’s water and milk and suggest that it’s a mark of the country’s aggressive dairy farming methods.

The white-coated director of the Hadassah Sperm Bank, Ruth Har-Nir, hunches over a microscope to view a freshly donated specimen and begins to methodically count each squiggly swimmer magnified on the slide.

She is checking the quality of a prospective donor, a young graduate student hoping to earn some extra cash. Though sophisticated lab machines could be used to analyze potency, Har-Nir says the old-fashioned method works best.

After a quick scan, she sits up straight and shakes her head. The number of spermatozoa darting around each tiny grid on the slide is two to four, well below the minimum six required, and nowhere near the 10 to 20 per grid that indicates the kind of healthy concentration the bank likes to see.

Also, rather than surging forward, some of the little guys flit left and right or just stall out, suggesting a weak motility.

“Under no circumstances can we accept sperm of this quality,” she says. In the previous three weeks, her bank tested six candidates and rejected all. “This is the trend,” she adds.

When Har-Nir helped launch the sperm bank in 1991, she says, it turned away about a third of the applicants for low quality. Using the same standard today, it would reject more than 80%. Though the bank relaxed its criteria, it still vetoes about two-thirds.

Har-Nir first noticed the problem a decade ago when she began rejecting more and more sperm from otherwise healthy young men. She shared her observations with local fertility doctors and their research has confirmed her suspicion.

Over the last 10 to 15 years, the concentration of sperm samples collected by the bank dropped 37% from 106 million cells per milliliter to 67 million, according to Dr. Ronit Haimov-Kochman, a leading Israeli infertility researcher at the Hadassah Hebrew University Medical Center.

Though declining sperm quality is an international phenomenon, the change in Israel is occurring at nearly twice the pace as other developed countries, Haimov-Kochman said. If current trends continue, she said, by 2030 the concentration of sperm from Israeli donors will drop below 20 million cells per milliliter, which many international health experts define as abnormal.

So far, there’s no evidence that declining sperm quality is resulting in fewer babies. The birthrate of Israel’s Jewish population has risen in recent decades, thanks largely to the increase in the number of ultra-Orthodox Jews, who tend to have large families.

Haimov-Kochman estimated that infertility rates in Israel have risen from 10% to 15% over the last 15 years, but says that’s in line with international trends. But she said male infertility — once believed to be the cause about half the time, just as in the U.S. — is now suspected in 70% of the cases here.

Most worrisome, she added, is that research so far has focused on sperm-bank donors, mostly students who are younger and healthier than the general population.

“If this is happening to the guys on our A-team, we might only be seeing the tip of the iceberg,” she said.

Sperm banks are struggling to cope. Rather than rely on walk-ins as they once did, they use marketing campaigns, posters in college sports centers and Facebook pages to attract virile candidates. The going rate for a donation has doubled over the last decade to about $270.

“The decline has been dramatic,” Cryobank’s Ronen said. “It’s a shame. We see these macho, beautiful guys come to give donations, but then we’re embarrassed to have to tell them that their sperm quality is so low they may actually end up coming back as a client.”

He’s capitalized on that, though, by offering to freeze sperm of young men with borderline quality who want to set aside a reserve in case their potency declines with age.

Har-Nir says her bank sometimes refers men with the most serious deficiencies for counseling or medical advice. But she emphasizes that rejection by the sperm bank doesn’t necessarily mean they won’t be able to have children naturally. It just means that their sperm isn’t, well, commercial quality.

Even with the drop in sperm quality being well documented, the cause remains unclear and the theories controversial. Some scientists fear that Israelis are being overexposed to female hormones.

“People in Israel are getting quite a load of estrogen,” said Laurence Shore, a retired hormone and toxicology researcher at the Kimron Veterinary Institute near Tel Aviv. “I don’t think it’s a good idea to expose children to such high levels of estrogen.”

He said that no studies so far have determined that estrogen levels in Israel are harming humans, adding that exposure may be too low for that. But he said it might be a factor in the sperm decline.

His research has found Israeli milk and associated products such as butter and cheese can contain 10 times as much estrogen as products from other countries because of Israel’s aggressive milk-production practices.

Israel is a world leader in producing milk, pumping twice as much from its cows as other parts of the world, he said. That’s partly because cows here are milked up to their eighth month of pregnancy, when natural estrogen levels in the milk soar, according to Shore. In nature, he said, cows usually stop giving milk to their own young when they are three months pregnant with a new calf.

Even though many other nations have adopted similar milking practices, Shore said, Israel is one of the first and most aggressive, so it could be seeing the effect sooner.

Haimov-Kochman is looking into water quality. As a tiny nation with a shortage of water, Israel reclaims much of its used water and sewage, which is processed, used in agriculture and may find its way back into groundwater.

The water, she says, has been found to contain traces of ethinyl estradiol, a synthetic estrogen used in birth control pills, which gets into the water through the urine of women taking the pills.

“You can’t clean this from the water,” she said.

Haimov-Kochman is also studying the effect of phthalates, chemicals used in plastic products that are suspected of affecting male reproductive development.

“But I can’t prove any of this,” she said.

Industry and government scientists dismiss fear about Israel’s water and milk as unfounded, saying levels are too small to affect humans.

“Only a tiny part of the total estrogen produced by the cows ends up in the milk,” said Dr. Stefan Soback, director of the Ministry of Agriculture’s National Residue Control Laboratory. “It is not sufficient to determine estrogen content in milk in order to claim physiological effects to somebody that consumes it.”

Haimov-Kochman worries that the government is not taking what’s happening seriously enough. She met with government officials a few years ago to discuss her findings, but there was no follow-up, she said.

“I don’t see any urgency about this from the government,” she said. “IVF [in vitro fertilization] is such a robust tool it can overcome bad sperm, so that’s reducing the pressure. But to me, it’s like putting your head in the sand.”

Meanwhile, sperm banks are struggling to stay afloat.

Said Haimov-Kochman, “If something isn’t done about this, Israel might find that its sperm banks can no longer survive.”

edmund.sanders@latimes.com

Batsheva Sobelman of The Times’ Jerusalem bureau contributed to this report.