What Is Horse Serum? Composition, Uses, and Benefits

Horse serum (HS) is the liquid fraction of horse blood that remains after clotting, once the cells and clotting factors are removed. In the lab it is used as a supplement in cell culture media, where it supplies the growth factors, hormones, attachment factors, and nutrients that many cell types need to grow and stay healthy. Along with fetal bovine serum (FBS), it is one of the two most widely used animal sera in cell culture.

Where horse serum comes from

Horse serum is collected from healthy donor horses. Blood is drawn, allowed to clot, and centrifuged so the straw-colored serum can be separated from the cells and fibrin. It is then sterile filtered and tested before release. Depending on the source animal, you will see fetal horse serum, newborn or donor horse serum, and adult horse serum, each with a slightly different profile.

What is in horse serum?

Horse serum is a complex, undefined mixture. Its main components include:

• Proteins such as albumin and globulins, which carry nutrients and support cell attachment
• Growth factors and hormones that signal cells to grow, divide, or differentiate
• Lipids, cholesterol, and fatty acids
• Amino acids, vitamins, and trace elements
• Transport proteins that shuttle iron, hormones, and other molecules

Compared with FBS, horse serum tends to be lower in some of the potent mitogens that drive rapid proliferation. That single difference is the reason it is preferred for several important applications.

What is horse serum used for?

Horse serum appears across cell biology, but a few uses stand out:

• Muscle cell differentiation. This is the classic use. Skeletal muscle myoblasts (for example the widely used C2C12 line) are expanded in FBS, then switched to low-serum media containing horse serum to trigger fusion into myotubes. The lower mitogen content helps push cells out of proliferation and into differentiation.
• Neuronal and glial cultures. Horse serum is used in a number of primary neuronal and glial protocols.
• Routine maintenance. For many cell lines it is a reliable, and often more economical, supplement for general culture.
• Immunology and hybridoma work. Horse serum has a long history in immunology, including use as a supplement and, historically, as a complement source.

Horse serum vs. FBS

The short version: FBS is richer in growth factors and is the default for rapid proliferation, while horse serum is lower in mitogens and is favored when you want cells to slow down and differentiate, or when you want a more economical and consistent supplement. Neither is universally better; the right choice depends on your cells and your goal. For a full side-by-side, see our guide on Horse Serum vs FBS.

Types of horse serum

Horse serum comes in several forms so you can match it to your protocol:

• Fetal, donor, and adult horse serum, which differ in growth-factor profile
• Heat-inactivated horse serum, treated at 56 degrees C to reduce complement activity
• Specialty grades such as endotoxin-depleted, dialyzed, lipid-depleted, and charcoal-stripped, for work that needs a more defined background

PurMa Biologics manufactures a full range, including premium, ultra-premium, and specialty horse serums, all made in the USA with a Certificate of Analysis on every lot.

Benefits of horse serum

• Promotes differentiation in muscle and other cell types
• Often more consistent lot to lot for its intended uses
• Frequently more economical than FBS
• A well-characterized, decades-proven supplement

How to choose and use it

Reach for horse serum when your protocol calls for differentiation (especially skeletal muscle), when you want a lower-mitogen background, or when cost and consistency matter for routine maintenance. Choose FBS when you need maximum growth. Store serum frozen at -20 degrees C, thaw it gently, and heat-inactivate only if your protocol requires it, since unnecessary heat inactivation can reduce performance. Keep the same lot across a set of experiments for the most consistent results.