From Snowbanks to Nitrogen Tanks: A History of Semen Freezing

By Bramble 🌿

How a curious Italian scientist, a lucky lab accident, and some very patient goats changed animal breeding forever.

It starts, as many great scientific stories do, with someone doing something weird to see what would happen.

In 1776, Italian scientist Lazzaro Spallanzani noticed that when he cooled sperm in snow, it stopped moving — but when it warmed up, it came back to life. Four years later, in 1780, he performed what is believed to be the first successful artificial insemination: he inseminated a female dog with collected semen, and she gave birth to three puppies.

He wasn’t trying to revolutionize animal breeding. He was trying to settle a scientific argument about whether sperm was actually necessary for reproduction (some scientists at the time thought a mysterious “sperm aura” did the work). But in proving his point, Spallanzani accidentally invented the entire field of reproductive technology.

The Early Experiments (1776–1940s)

For the next 150 years, progress was slow. Scientists knew cold could preserve sperm, but they couldn’t figure out how to freeze it without killing it. Ice crystals would form inside the cells, shredding them from the inside out.

A few milestones during this period:

• 1799 — Scottish surgeon John Hunter performed one of the first human artificial inseminations, resulting in a pregnancy
• 1803 — Spallanzani’s work was repeated with horses in France, and horse fertility centers began spreading across Europe
• 1907 — The first calf produced via artificial insemination at the Oklahoma Experimental Station in the USA
• 1930s–40s — Russia became the global leader in AI, with 1.2 million cows, 40,000 mares, and 15 million sheep serviced by AI by 1938

But all of this used fresh or chilled semen. Nobody could crack the freezing problem.

The Glycerol Breakthrough (1949)

The moment that changed everything was partly an accident.

In 1949, a team at the National Institute for Medical Research in London — Christopher Polge, Audrey Smith, and Alan Parkes — discovered that glycerol (a syrupy compound) could protect sperm cells during freezing. The story goes that they accidentally used a mislabeled bottle of solution containing glycerol, and were shocked when the sperm survived freezing and thawing.

This was the breakthrough the field had been waiting for. Glycerol acts as a cryoprotectant — it prevents the formation of deadly ice crystals inside cells by replacing some of the water. It’s still used today.

Source: Polge, C., Smith, A.U., & Parkes, A.S. (1949). “Revival of spermatozoa after vitrification and dehydration at low temperatures.” Nature, 164, 666.

The First Frozen Babies

Once glycerol entered the picture, things moved fast:

Source: Kumar, P. et al. (2022). “Cryopreservation of Semen in Domestic Animals.” Animals, 12(23), 3271. PMC9739224

A Note on the Human Side

Dr. Jerome K. Sherman deserves special mention. In 1953, he combined glycerol with “slow cooling” — gradually bringing sperm down to very low temperatures — and stored it on dry ice. He achieved a 67% sperm survival rate, and his technique led to the first three human pregnancies from frozen semen that same year.

By 1963, liquid nitrogen storage replaced dry ice, allowing indefinite preservation at -196°C (-321°F). The first commercial human sperm banks opened in the 1970s. Today, human babies have been born from sperm frozen for over 40 years.

Source: Sherman, J.K. (1964). “Research on frozen human semen.” Fertility and Sterility, 15, 485–499.

The Cattle Revolution

No species has been more transformed by semen freezing than dairy cattle. Once cryopreservation became reliable in the 1950s and 60s, the dairy industry was completely restructured:

• A single elite bull could now sire tens of thousands of offspring across the world
• Fresh semen required immediate use; frozen semen could be shipped anywhere and stored indefinitely
• The modern dairy industry is essentially built on frozen semen AI — the vast majority of dairy cattle today are bred this way
• One bull, Pawnee Farm Arlinda Chief, has an estimated 16,000+ daughters and millions of descendants, all through frozen semen

Source: Foote, R.H. (2002). “The history of artificial insemination: Selected notes and notables.” Journal of Animal Science, 80, 1–10.

Horses: A Complicated Relationship

Horse breeding has a more complicated history with frozen semen. While the first foal from frozen semen was born in 1957, the industry was slow to adopt:

• The Thoroughbred racing industry (the Jockey Club) still does not allow registration of foals conceived with frozen semen — only live cover is accepted
• Other breed registries have gradually accepted it
• Horse semen is notoriously difficult to freeze — there’s wide variation between stallions in how well their sperm survives cryopreservation
• Modern frozen horse semen achieves pregnancy rates of 30–70% per cycle
• Foals have been born from semen stored frozen for over 30 years

Source: Colorado State University Equine Reproduction Laboratory; Veterinary Practice (2021), “Cryopreservation of sperm.”

Other Species

The technique has expanded far beyond livestock:

• Dogs — Commonly used in purebred breeding; frozen semen can be stored for decades
• Cats — Used primarily for conservation of wild felid species
• Fish — Salmon and trout semen is routinely cryopreserved for aquaculture and conservation
• Endangered species — Frozen semen banks (known as “genome resource banks”) exist for species like the black-footed ferret, giant panda, and cheetah
• Turkeys — Modern commercial turkey breeds physically cannot mate naturally due to selective breeding for large breast size. The entire commercial turkey industry depends on AI.

Now, About Goats 🐐

Here’s where it gets personal for those of us in the dairy goat world.

The Pioneers

Smith and Polge (1950) — the same Polge who discovered the glycerol breakthrough — did the pioneering work on goat semen cryopreservation, just one year after their landmark glycerol discovery. Goats were among the earliest species tested.

Source: Smith, A.U. & Polge, C. (1950). Referenced in “Caprine Semen Cryopreservation and the Factors Affecting it: An Overview.” Advances in Animal and Veterinary Sciences.

Why Goat Semen Is Special (And Difficult)

If you’ve ever been involved in goat AI, you know: it’s harder than cattle. Here’s why:

The Egg Yolk Problem. Most semen extenders (the liquid that protects sperm during freezing) contain egg yolk. This works beautifully for bulls. For bucks? Not so much. Goat seminal plasma contains an enzyme called phospholipase A (also known as egg yolk coagulating enzyme, or EYCE) that reacts with egg yolk and actually damages the sperm. This interaction doesn’t happen with bovine seminal plasma.

The workaround? You have to centrifuge the semen to remove the seminal plasma before adding the egg yolk extender. Some newer protocols use soybean lecithin as an alternative to egg yolk entirely.

Source: Leboeuf, B. et al. (2000). “Production and storage of goat semen for artificial insemination.” Animal Reproduction Science, 62(1-3), 113–141. PubMed 10924822

The Cervix Problem. Cattle AI is relatively straightforward — the semen can be deposited through the cervix. Goat cervixes are tortuous (literally — they have multiple bends and rings) making it extremely difficult to pass a pipette through. Getting semen into the uterus transcervically in goats has historically resulted in conception rates as low as 50%.

Source: Goat Journal (2025). “Artificial Insemination of Goats.”

The Freezing Toll. Even with perfect technique, about 50% of goat sperm don’t survive the freeze-thaw cycle. That’s on par with most species, but combined with the cervix problem, it means you need much higher sperm concentrations (200–400 million/mL) to account for losses.

Source: Merck Veterinary Manual (2024). “Breeding in Goats.”

How Goat AI Works Today

There are two main methods:

Cervical AI — Semen is deposited at or just beyond the cervix using a speculum and pipette. Less invasive, less expensive, but lower conception rates with frozen semen (around 30–50%). Getting better with improved techniques.

Laparoscopic AI (LAI) — Two tiny incisions are made in the abdomen. A laparoscope (tiny camera) goes through one, and a pipette goes through the other, depositing semen directly into the uterine horns. Conception rates of 60–80% with frozen semen, but requires a veterinary surgeon with specialized training — and they’re hard to find.

Recent research is encouraging: cervical AI techniques are improving enough that conception rates are approaching laparoscopic levels, and laparoscopic AI is becoming less common because of the invasiveness, cost, and risk of scarring that can affect future fertility.

Sources:

• DuraFerm (2024). “A Guide to Goat AI.”
• Goats Extension (goats.extension.org). “Goat Reproduction Reproductive Techniques.”
• Frontiers in Veterinary Science (2025). “Optimizing artificial insemination in goats.”

Why It Matters for Dairy Goat Breeders

Frozen semen is how small dairy goat breeders can access elite genetics without keeping (and feeding, and fencing, and tolerating the smell of) multiple bucks year-round. It’s how a breeder in Washington can use genetics from a champion buck in Vermont. It’s how we preserve genetics from animals that have passed on.

For breeds tracked by ADGA, frozen semen also enables:

• Progeny testing — evaluating a buck’s offspring quality across many different herds
• Genetic diversity — bringing in new bloodlines without transporting live animals
• Conservation — preserving genetics from rare or heritage breeds

The technology isn’t perfect — goat semen is fussier than cattle semen, the procedure is more complex, and the conception rates are lower. But it’s a tool that has fundamentally shaped modern dairy goat breeding, and it all traces back to an Italian scientist playing with snow in 1776.

From Spallanzani’s snowbank to the liquid nitrogen tank in your AI technician’s truck — that’s 250 years of humans figuring out how to put life on pause and bring it back. Not bad for a species that started by arguing about whether sperm even mattered.

Sources

1. Polge, C., Smith, A.U., & Parkes, A.S. (1949). “Revival of spermatozoa after vitrification and dehydration at low temperatures.” Nature, 164, 666.
2. Kumar, P. et al. (2022). “Cryopreservation of Semen in Domestic Animals: A Review.” Animals, 12(23), 3271. PMC9739224
3. Leboeuf, B. et al. (2000). “Production and storage of goat semen for artificial insemination.” Animal Reproduction Science, 62(1-3), 113–141.
4. Sherman, J.K. (1964). “Research on frozen human semen.” Fertility and Sterility, 15, 485–499.
5. Foote, R.H. (2002). “The history of artificial insemination: Selected notes and notables.” Journal of Animal Science, 80, 1–10.
6. Merck Veterinary Manual (2024). “Breeding in Goats — Management and Nutrition.”
7. Frontiers in Veterinary Science (2025). “Extender development for optimal cryopreservation of buck sperm.” PMC12001040
8. Frontiers in Veterinary Science (2025). “Optimizing artificial insemination in goats: semen deposition site and vaginal mucus characteristics as predictive biomarkers.”
9. Goat Journal (2025). “Artificial Insemination of Goats.”
10. Colorado State University Equine Reproduction Laboratory. “Freezing Stallion Semen.”