Anti-diarrheal products for calves contain various substances designed to relieve the symptoms of diarrhea and promote gastrointestinal health. Here is a list of substances, that can be used in prevention or combating diarrheas in calves.

1. Pectins: Pectins are a type of plant fiber found mainly in fruits and vegetables. In anti-diarrheal products for calves, pectin can help maintain proper stool consistency. It acts as an agent to increase the viscosity of the digestive contents, which can help stop excessive flow of digestive contents through the digestive tract.
2. Chestnut tannins: Tannins are plant compounds that are found in a variety of plants, including chestnuts. They have astringent properties, which means they can help fight diarrhea by reducing inflammation and relieving irritation of the gastrointestinal mucosa.
3. Oak bark: Oak bark is a source of tannins, as is chestnut. These substances have an astringent effect, which can help reduce fluid flow through the digestive tract and relieve inflammation.
4. Electrolytes: When diarrhea occurs, the body can lose a lot of fluids and electrolytes, which can lead to dehydration. Anti-diarrheal products for calves contain electrolytes such as sodium, potassium and chloride to help restore the body's electrolyte balance.
5. Glucose: Glucose is a source of energy for the body. In the case of diarrhea, the body can lose a lot of energy with fluids, so the addition of glucose can help provide enough energy for calves.
6. Probiotics: Probiotics are live microorganisms that, when introduced into the digestive tract, can help restore healthy intestinal microflora. They can also compete with harmful bacteria and improve digestion.
7. Prebiotics: Prebiotics are substances that provide food for probiotics. They help probiotics develop and function in the digestive tract. An example of a prebiotic would be fructooligosaccharide.

It is worth noting that anti-diarrheal products for calves often contain combinations of these substances to provide comprehensive support for gastrointestinal health and help quickly relieve diarrhea symptoms. However, they should always be used according to your veterinarian's recommendations to ensure proper dosage and treatment tailored to the individual calf's needs.