Why are only horses used for serum production?

by Butantan Team

Published: October 14, 2021

In the late 1890s, the discovery of serum therapy brought a cure for diphtheria, a disease that spread rapidly among children and killed half of those who fell ill. To elaborate these drugs, antibodies produced by animals were used. As cases of diphtheria in the 19th century were numerous, large quantities of serum production became necessary, and scientists realized that they needed to use a robust animal for the job. And the question remained: which animal could be used for this purpose? That’s where the horse enters the story.

Mammals, which have an immune system very similar to each other, have a greater capacity to produce antibodies and end up being more resistant. There is also a simple matter of size: the more blood the animal has circulating in the body, the greater the amount of plasma (part of the blood in which the antibodies are located) and, therefore, the greater the production of serum.

Horses have the size and strength necessary to tolerate the entire process of obtaining plasma well. What’s more, they are calm and easy to control, and can be trained for the activity that scientists need.

The process begins when small doses containing the poison, virus or bacteria to be fought by the human body are applied to the horse; the horse produces the antibody against the disease or the toxins from the poison; the animal’s antibody-rich plasma is collected. This plasma undergoes chemical and physical procedures until it becomes a serum that can be used to treat people’s health.

Butantan produces 13 different types of serum, including anti-venom (against snake venom), anti-scorpion (scorpion), anti-arachnidic (spider and scorpion), antilonomic (caterpillar), antidiphtheria (diphtheria), anti-tetanus (tetanus), anti-botulinum (botulism) and rabies (rabies), in addition to combined versions. And since 1901 he has had the help of horses for that. They stay at the São Joaquim Farm, owned by Butantan in the interior of São Paulo, and work as if they were donating blood, only a quantity of plasma being removed that does not harm the animal. After all the process, they spend 40 days just resting and eating.

In 2018, the collection of plasma from horses was automated, improving the quality of the raw material. Currently, it is done through plasmapheresis, a process in which veterinarians use equipment that collects blood, separates the plasma containing the antibodies and returns the red blood cells, platelets and other elements to the animal, all done in a continuous cycle. , so that the horse is not weakened by the removal of the plasma.

Horses work in groups and each group works to produce a specific serum. If, for example, a collection was made for anti-rabies serum, these animals will always be used for this purpose.

Generally, Butantan horses are not of a specific breed. Horses go through an approval process (criteria such as minimum height, proportional weight, blood tests and veterinary care are also important at this time) and it is up to Butantan to select these future plasma donors.

Horses start donating plasma from the age of five and retire at about 20 years of age. And they are very well cared for: they are always brushed, vaccinated, well fed and monitored so they don’t have worms or parasites.

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