Hormone

They are substances that travel through the animal's body in order to regulate and coordinate its multiple functions. These biochemical substances are produced in endocrine glands and transported by the circulatory system, causing specific activation or regulation effects in other organs or parts of the body. For instance, when the sow becomes pregnant, there is an increase in the production of a hormone that tells the body: "I am pregnant." This situation causes a series of changes as, for example, the interruption of the oestrous cycle, the non-acceptance of the boar, etc.

There are also synthetic hormones which may be administered to the animals for controlling their oestrous cycle, inducing farrowings, stimulating milk production, etc.