Fetal bovine serum (FBS) is one of the most widely used supplements in cell culture and biotechnology. It serves as a nutrient-rich solution that supports the growth, proliferation, and maintenance of cells in vitro. Often referred to as the "gold standard" in cell culture supplementation, fetal bovine serum has been essential in biomedical research, pharmaceutical and vaccine development, and biotechnology since the mid-20th century.
In this article, we will explore the history and uses of FBS, how it is sourced and produced, and its importance in cell culture.
What is FBS used for?
FBS is a widely used supplement in mammalian cell culture in biotechnology, pharmaceutical production, medical research, and other life-science fields. It is derived from fetal cattle and is the liquid part of the blood that remains after coagulation. FBS is rich in nutrients, growth factors, hormones, and proteins, making it highly useful for growth and maintenance of cells grown in vitro. Compared to sera from adult cattle or from other animals, FBS also contains low levels of gamma-globulins and other antibodies that can interfere with cell growth.
What does FBS stand for?
- Fetal indicates that the serum is collected from fetal cows, not adult cattle or calves.
- Bovine refers to the species source: cattle (Bos taurus). Sera from other animals (e.g., horse, rabbit) are also used in cell culture, but not as frequently as FBS.
- Serum is the fluid component of blood that remains after coagulation. Serum lacks red and white blood cells and clotting factors but retains a broad spectrum of biological molecules essential for cell culture.
History of FBS use in cell culture
The use of FBS in cell culture emerged during the mid-20th century (Table 1). Nearly 50 years earlier, scientists had figured out how to maintain long-term growth of chicken embryonic cell cultures by supplementing the culture media with blood plasma from adult chickens. Their discovery fed into a larger effort to identify the precise components needed for successful culture of animal cells in vitro, which led to many of the media formulations still in use today.
In the late1950s, a geneticist named Theodore Puck and his colleagues published a paper that described the use of FBS in a protocol for growing and maintaining mammalian cells for long periods without chromosomal abnormalities. The use of FBS soon became widespread in cell culture laboratories. At the same time, efforts to understand its composition more precisely and to develop synthetic (also called “characterized”) alternatives continued apace (and still do). Researchers continue to explore the question of whether FBS can be fully replaced with alternatives.
What is FBS made of?
FBS is a highly complex fluid. Its numerous components include nutrients, proteins, hormones, and growth factors. This mix of components is what makes FBS so useful for maintaining cell viability, promoting proliferation, and supporting differentiation in a wide range of mammalian cell types.
FBS is undefined, meaning its composition varies by batch. Table 1 describes some of the key components of FBS and their roles in cell culture.
Fig 1. Components of FBS
| Type | Examples | Functions |
| Blood albumin (carrier protein) | Bovine serum albumin | Transport nutrients, maintain osmotic pressure, stabilize cells |
| Growth factors | IGF, FGF, EGF | Stimulate cell division, differentiation, and growth |
| Attachment factors | Fibronectin, laminin, vitronectin, collagen | Support cell adhesion and proliferation |
| Hormones | Insulin, glucagon, growth hormones | Regulate metabolism and developmental pathways |
| Lipids | Cholesterol, triglycerides | Cell membrane synthesis, energy metabolism |
| Vitamins | A, B, C | Enzymatic co-factors, antioxidants |
| Carbohydrates | Fructose, glucose | Energy source and signaling molecule |
| Minerals | Calcium, iron, magnesium | Cell proliferation and other processes |
Categories of bovine serum
Bovine serum is categorized primarily by the age of the animal it comes from. In addition to FBS, newborn calf serum, calf serum, and adult bovine serum are also used in life science applications. Each type of serum has distinct characteristics that influence its use and utility in different applications.
1) Fetal bovine serum
FBS is collected from bovine fetuses when pregnant cows are slaughtered. It supports a wide range of cell types, including sensitive primary cells, stem cells, and hybridomas. Because of its ability to stimulate cell proliferation and reduce immune reactions, it remains the most widely used serum supplement in mammalian cell culture applications.
2) Newborn calf serum (NCS)
ISIA defines NCS as serum from the blood of healthy calves that are no more than 20 days old. The exact age of the calves varies by manufacturer, for example, HyClone™ newborn bovine calf serum is typically sourced from 10-day-old calves. Compared to FBS, NCS contains higher levels of antibodies and lower levels of growth factors.
NCS is often used when cell growth is robust and when cost is a consideration. While it is more affordable, its higher antibody content can sometimes interfere with sensitive or primary cell lines.
3) Adult bovine serum
Adult bovine serum is collected from cattle that are at least 12 months of age. This serum is characterized by higher levels of immunoglobulins, complement proteins, and other immune components than FBS, as well as a lower concentration of growth factors. Like fetal calf serum, adult bovine serum is used primarily for robust, well-established cell lines that are less sensitive to antibody interference. It is typically the most cost-effective option among bovine sera.
Uses of fetal bovine serum
As we’ve described above, FBS is a key growth medium supplement in mammalian cell culture, so it is used widely across life-science research and biopharma development and manufacturing. Some uses include:
- Vaccine production: Enhances viral yield and stability by supporting cell line health and productivity.
- Biopharmaceutical manufacturing: Supports growth of mammalian cells producing therapeutic proteins, monoclonal antibodies, and other biologics.
- Tissue engineering and regenerative medicine: Promotes proliferation and differentiation of stem and progenitor cells.
- Toxicology and drug development: Supports assays for cytotoxicity, pharmacodynamics, and cellular responses.
What to know about using FBS in cell culture
- Batch variability: Even with stringent quality control and regulations regarding its collection and processing, FBS is subject to batch-to-batch variation. Pre-testing and screening of new serum batches can help support consistent experimental outcomes.
- Ethical and scientific considerations: Because FBS is a by-product of the meat industry, its use in cell culture has raised concerns about long-term environmental sustainability and animal welfare. Moreover, the variable composition of FBS can influence the results of cell culture experiments.
- Serum-free alternatives: Serum-free or chemically defined media offer a more controlled and ethically sound option for certain applications. Nevertheless, many cell types continue to require FBS for optimal growth and viability.
- Contamination risks: FBS carries the potential for contamination with viruses, mycoplasma, or endotoxins. Regulatory requirements for testing are designed to help mitigate these risks, with more rigorous testing required for products intended for use in biopharma manufacturing. Viral contamination risks vary by geographical source, so different tests are required for sera from different parts of the world.
- Heat inactivation: Protocols may call for heat inactivation to neutralize complement proteins harmful to cells. However, this process can also diminish beneficial components, making it essential to weigh the benefits against potential drawbacks based on experimental needs.
- Storage and handling: Proper storage is crucial to preserve FBS activity. Repeated freeze-thaw cycles should be avoided to maintain quality and performance. Always read and follow the manufacturer’s instructions on handling and storage.
- Concentration optimization: FBS is typically used at concentrations between 5% and 20%, depending on the cell type. Both insufficient and excessive supplementation can negatively impact cell behavior and data reliability.
- Regulatory compliance: In clinical and pharmaceutical contexts, FBS use must align with regulatory standards to ensure product safety, traceability, and ethical sourcing.
How is FBS collected and manufactured?
Fetal bovine serum (FBS) is collected and manufactured through a highly controlled process to ensure purity, safety, and biological activity. It starts with sourcing fetal blood from bovine fetuses at slaughterhouses during the processing of pregnant cows.
Blood is collected under strict regulations to minimize both animal suffering and contamination. Sterile cardiac puncture is used to draw blood directly from the fetal heart, providing high volume with minimal contamination.
The blood is allowed to clot, and serum is separated by centrifugation. It is then filtered to remove particulates and microbes. Heat inactivation and/or gamma irradiation may also be used.
The serum is tested for sterility, endotoxins, viruses, and biochemical profile to ensure safety and consistency. It is aliquoted into sterile containers and rapidly frozen to preserve activity. Each batch is required to meet regulatory and quality standards.
How is FBS stored and handled?
Proper storage and handling are essential to maintain the quality and biological activity of fetal bovine serum (FBS). Upon receipt, FBS should be frozen at -20°C or -80°C to preserve sensitive components such as growth factors and hormones.
To prevent protein degradation, freeze-thaw cycles should be minimized by aliquoting serum into smaller volumes. Thawing should be done gradually, preferably in a refrigerator or cold water, and the serum gently mixed to ensure consistency without introducing air bubbles.
Once thawed, FBS should be stored at 2-8°C and used within 4-6 weeks. Aseptic handling is crucial to avoid contamination, and proper labeling ensures traceability and quality control. Adhering to these practices supports the reliability of cell culture experiments.
Regulation of fetal bovine serum collection and manufacturing
Regulation of FBS is complex and varies by country. Key regulatory bodies include:
- US Department of Agriculture (USDA)
Oversees animal welfare during FBS collection and regulates import/export controls to prevent disease spread.
- European Medicines Agency (EMA)
Regulates the use of FBS in pharmaceutical manufacturing, ensuring compliance with safety and quality standards.
- International Serum Industry Association (ISIA)
Sets global standards for ethical sourcing and traceability of FBS within the industry.
- US Food and Drug Administration
Issues regulations to ensure consistent quality, safety, and regulatory compliance during manufacturing.
Conclusion
Fetal bovine serum (FBS) has been a cornerstone of cell culture for decades, offering a rich and complex blend of nutrients, growth factors, and bioactive molecules that enable robust cell growth and maintenance. Its unique composition and reliable performance make it indispensable for a wide range of applications, from basic research to pharmaceutical manufacturing.
However, the use of FBS is accompanied by important ethical, scientific, and practical considerations. These include concerns about animal welfare, batch variability, and the risk of contamination, which require careful management through rigorous quality control and regulatory oversight.
Looking ahead, while emerging alternatives offer promising options, FBS continues to play a vital role in advancing biological and medical research. Responsible sourcing, improved manufacturing practices, and ongoing innovation will ensure that FBS remains a key resource, bridging the gap between traditional methods and future cell culture technologies.
Frequently asked questions
1. What is the purpose of bovine serum?
Bovine serum provides essential nutrients, hormones, and growth factors that promote the survival, proliferation, and differentiation of cultured cells. It supports physiological conditions in vitro.
2. What is the difference between BSA and FBS?
BSA (bovine serum albumin) is a single purified protein found in bovine serum, while FBS is a complex mixture of proteins, hormones, lipids, and other nutrients. BSA is often used as a stabilizer or blocking agent, whereas FBS is used as a complete cell culture supplement.
3. What is the composition of FBS?
FBS contains proteins (albumin, globulins), growth factors (IGF, FGF), hormones (insulin), lipids, vitamins, minerals, amino acids, and other nutrients. The exact composition varies by batch and source.
4. Why is fetal bovine serum used in vaccines?
FBS supports the growth of virus-producing cells during vaccine development. Its nutrients and low immunoglobulin levels make it ideal for cultivating viruses without interfering immune components.
5. What is the difference between FCS and FBS in cell culture?
The terms FCS (fetal calf serum) and FBS (fetal bovine serum) are often used interchangeably, but FBS is more precise, as “calf” and “fetus” describe different developmental stages.