How Is Fetal Bovine Serum (FBS) Collected?

Fetal bovine serum is collected by inserting a needle into the heart of a calf fetus after its pregnant mother has been slaughtered at an abattoir, a procedure known as cardiac puncture. The fetus is typically discovered incidentally during meat processing, making FBS a by-product of the cattle industry rather than a product animals are specifically raised for. The process involves strict sterile handling, cold storage to promote clotting, and centrifugation to separate the clear yellowish serum from blood cells and clotting factors. Simple as it sounds in outline, the reality of how FBS reaches a laboratory is shaped by slaughterhouse logistics, welfare debates, quality-control headaches, and a global supply chain that has grown increasingly strained.

Why FBS Matters for Cell Culture

Before getting into the collection process itself, it helps to understand why researchers go to such lengths to obtain this particular fluid. FBS contains a rich cocktail of growth factors, hormones, nutrients, and attachment proteins that keep cells alive and dividing in a lab dish. Critically, because a fetus has not yet developed a fully functioning immune system, FBS carries very low levels of antibodies. That means it can nourish cells from many different species without triggering an immune reaction that would kill the culture.¹ This combination of abundant growth signals and minimal immune interference is what made FBS the default supplement in biomedical research for decades, powering everything from vaccine production to cancer drug screening.

Step by Step Through the Collection

The entire process begins not in a specialized serum facility but on the kill floor of a commercial slaughterhouse. The pregnant cow is slaughtered for meat in the normal way, and the pregnancy is often only discovered afterward. In many countries, this collection can only take place in government-approved facilities to prevent unregulated harvesting of fetuses.¹

Once the fetus is removed from the uterus, it is transferred to a sterile workspace. A large-gauge needle is inserted directly into the fetal heart, and blood is drawn out. This cardiac puncture technique is standard across the industry.² The blood may be collected into sterile tubes or specialized blood bags containing anticoagulant, depending on the facility’s protocol. One documented setup uses bags with trisodium citrate, citric acid, and dextrose to keep the blood from clotting prematurely during transport.³

After collection, the blood is sealed in sterile packaging and refrigerated. Cold storage encourages the blood to clot naturally over a controlled period. Once clotting is complete, the mixture is centrifuged in a refrigerated centrifuge, which separates three layers: a dense pellet of red blood cells and other cellular debris at the bottom, a middle layer of clotting factors, and a clear golden-yellow liquid on top. That liquid is the serum. It is carefully drawn off, pooled from multiple fetuses to create commercial lots, filtered to remove bacteria, and subjected to quality testing before being bottled and sold to laboratories worldwide.

The Animal Welfare Debate

The ethics of FBS collection have been debated for years, and the central question is whether the fetus experiences suffering during the blood draw. A fetus inside the uterus exists in a low-oxygen environment and is not breathing air. Research indicates that a fetal calf can only suffer if it inflates its lungs with air after removal from the uterus, raising its blood oxygen to levels compatible with consciousness. Preventing the fetus from taking that first breath, or killing it by an efficient method before blood collection, is considered sufficient to ensure the procedure is humane.⁴

In practice, though, the speed and conditions of slaughterhouse work make consistent adherence to these safeguards difficult to verify. There is ongoing debate about whether fetal calves suffer during the interval between the dam’s slaughter and the cardiac puncture.⁵ Some animal-welfare advocates argue that the very existence of a commercial market for fetal blood creates an incentive structure that conflicts with humane handling, even if the guidelines themselves are well-intentioned. Others counter that because FBS is a by-product of animals already destined for slaughter, banning it would not reduce animal deaths but would cripple biomedical research until alternatives mature.

Quality Testing and What Can Go Wrong

Raw serum is only the starting material. Before a batch can be sold for research use, it must pass a battery of tests. Laboratories screen for mycoplasma contamination and a long list of adventitious viruses, including bovine pestiviruses, bovine adenovirus, bluetongue virus, bovine herpesvirus, bovine parvovirus, and several others. Testing methods include growing cells in the serum and then checking for viral signatures using immunofluorescence, as well as molecular detection for mycoplasma and pestiviruses.⁶ Some manufacturers also gamma-irradiate the serum to inactivate any pathogens that might survive filtration.

Even after all that testing, one persistent problem plagues researchers: batch-to-batch variability. Because FBS is pooled from different fetuses of different ages and health statuses, no two batches are chemically identical. The exact composition of growth factors, hormones, and trace proteins varies in ways that are largely unknown to the end user. No recognized universal standard for FBS composition exists, which means cells grown in one lab’s batch may behave differently from cells grown in another’s. This is not a minor annoyance. It directly undermines the reproducibility of experimental results across different research groups.⁷

Researchers often cope by buying large reserves of a single batch and “qualifying” it against their specific cell line before committing. But when that batch runs out, switching to a new one can change experimental outcomes in subtle and frustrating ways. This variability problem is one of the strongest scientific arguments, separate from the ethical ones, for moving away from FBS altogether.

Geographic Origin and Supply-Chain Fraud

FBS is collected on every continent where cattle are commercially slaughtered, but the geographic origin matters more than you might expect. Different countries carry different risks of bovine diseases, and some regions command premium prices because they are considered lower-risk. Australia, New Zealand, and parts of South America are generally regarded as having favorable disease profiles. Regulatory agencies in many countries require that imported FBS come from regions free of specific diseases like bovine spongiform encephalopathy.

This creates an incentive for fraud. Serum collected in a higher-risk region can be relabeled as originating from a lower-risk one, fetching a higher price. In response, the International Serum Industry Association worked with a third-party testing firm to develop a method for verifying the geographic origin of serum products using trace-element and isotope analysis.⁸ The technique works because the mineral composition of soil and water varies by region, and those signatures end up in the blood of cattle that graze there. It is essentially a geographic fingerprint for serum. While this has helped reduce fraud, the global supply chain remains opaque enough that researchers are advised to buy only from reputable suppliers with documented traceability.

A Tightening Supply

The FBS market is under pressure from several directions at once. Because FBS comes from pregnant cows sent to slaughter, its supply depends on how many pregnant cows are culled from herds in a given year. When calf prices are high, producers have a strong financial incentive to let pregnant cows deliver their calves alive rather than send them to slaughter. Recent years have seen historically high calf prices in major cattle-producing countries, which directly reduces the number of fetuses available for serum collection.⁹

Technology is squeezing supply further. The widespread adoption of sexed semen in dairy operations allows farmers to choose the sex of calves with high accuracy. Dairies use female-sexed semen to produce just enough replacement heifers and then breed remaining cows to beef sires, producing crossbred calves whose market value has risen sharply. Because those calves are now worth substantially more than they used to be, dairy operators increasingly hold pregnant cull cows until the calf is born rather than shipping them to slaughter while pregnant.⁹ The net effect is fewer fetal calves at slaughter, less raw material for FBS, and upward price pressure on an already expensive product.

This supply squeeze matters because FBS remains deeply embedded in global biomedical research, pharmaceutical manufacturing, and the emerging field of cellular agriculture. Large-scale production of cultivated meat, for instance, would require enormous volumes of growth media, and a continued reliance on FBS would be both economically unsustainable and ethically problematic.¹⁰

Alternatives That Are Gaining Ground

The search for FBS replacements has been underway for decades, and the options have improved considerably, though none has achieved a universal drop-in replacement status yet.

Chemically defined media are formulations in which every ingredient is known at a precise concentration, eliminating the “mystery cocktail” problem of FBS. Some commercially available versions can maintain and differentiate various cell types, including neuronal lineages and certain cancer cell lines, without any serum or animal products at all.¹¹ Their appeal is obvious: controlled composition means more reproducible experiments. One comparison of adipose-derived stem cells grown in serum-free chemically defined media versus FBS-containing media found that the serum-free version produced more cells in less time, with a more stable growth rate and a more uniform cell population.¹²

The catch is that developing a defined medium for a new cell type is slow, expensive, and often done in isolation. Manufacturers sometimes keep their formulations proprietary, meaning a medium marketed as “defined” may not be fully transparent about what it contains.¹³ That partly undermines the reproducibility advantage. Efforts to coordinate development across labs and share formulation data have been proposed, but progress has been incremental.

Human platelet lysate is another alternative that has gained traction, especially for stem cell work. It is made from donated or expired human platelets, which are lysed (broken open) to release their growth factors. Studies have shown that human platelet lysate can support cell proliferation at levels equal to or exceeding those achieved with FBS. In one study of adipose-derived stromal cells, a concentration of just 0.75% human platelet lysate matched the performance of a standard 10% FBS supplement in terms of cell growth, surface-marker profile, and the ability to differentiate into bone, fat, and cartilage lineages.¹⁴ Cancer-cell work has also shown promising results, with cells cultured in human platelet lysate displaying nearly identical protein profiles and drug sensitivities compared to cells grown in FBS.¹⁵

Human platelet lysate has the added advantage of being derived from a human source, which matters when the cultured cells are intended for human therapies. Using animal serum in the production of cells destined for transplantation into a patient introduces regulatory complications and the theoretical risk of transmitting animal pathogens. Switching to a human-derived supplement sidesteps both issues.

Why FBS Has Not Disappeared Yet

Given the ethical concerns, the variability headaches, the tightening supply, and the improving alternatives, you might wonder why FBS is still so widely used. The answer is inertia and breadth. FBS works across a remarkably wide range of cell types and experimental setups. A researcher starting a new project with an unfamiliar cell line can add FBS to a standard basal medium and have a reasonable expectation that cells will grow. Serum-free media, by contrast, often need to be optimized for each specific cell type, which takes time and specialized knowledge.

There is also a legacy-data problem. Decades of published literature describe experiments performed with FBS. If you switch to a serum-free medium, your results may not be directly comparable to the vast body of prior work in your field, which creates a professional disincentive to change. Journal reviewers and regulatory agencies may question whether your serum-free data can be compared to historical FBS-based data, adding friction to the transition.

Cost is sometimes cited as a barrier to alternatives, though this is becoming less convincing. FBS itself is expensive, and its price has been climbing as supply tightens. Some chemically defined media are now competitively priced, especially when factoring in the time saved by not having to qualify each new FBS batch.

The Cellular Agriculture Bottleneck

Nowhere is the FBS problem more visible than in the young field of cultivated meat, which aims to grow animal muscle tissue in bioreactors instead of raising and slaughtering livestock. The entire premise depends on being able to culture animal cells at massive scale, and the growth media those cells live in is one of the largest cost drivers. Relying on FBS for commercial-scale cultivated meat would be both absurdly expensive and philosophically contradictory, since the point is to reduce animal slaughter.¹⁰

Startups in this space have poured significant investment into developing proprietary serum-free media tailored to muscle and fat cell growth. Progress has been real but uneven. Some companies claim to have achieved serum-free production at pilot scale, but detailed formulations are rarely published, and independent verification is limited. The challenge is not just getting cells to survive without FBS but getting them to proliferate quickly, differentiate into the right tissue types, and do so at a cost that could eventually compete with conventional meat. Each of those requirements adds layers of difficulty to medium design.

The broader trajectory seems clear: FBS will gradually be replaced across most applications, driven by a convergence of ethical pressure, supply constraints, reproducibility demands, and the specific needs of industries like cellular agriculture that simply cannot scale with an animal-derived ingredient. How quickly that transition happens depends largely on how fast serum-free formulations can be developed and validated for the hundreds of cell types that currently depend on FBS, and how willing the research community is to absorb the short-term costs of switching.