OK, I'll bite.
The gestation and birth of a foal (baby horse). The foal during its gestation from the fertilized egg is protected from infection by the placental barrier. As the mare (that's a mother horse) is exposed by her environment to various organisms, she creates appropriate antibodies to the infectious agents. The foal, however, is not exposed to these infections or anti-bodies as this might interfere with the correct genetic instructions to insure the foal does not develop deformed.
When the foal is born, it has no immunity. It's first suckle from its mare, called collustrum has all the antibodies the mare has evolved during gestation. The colts (male) of filly's (female) first drink is its vaccination.
During the birthing of horses, I am always aware of the wonder of this beautiful design for the foal to grow in a secure environment while the mare manufactures the vaccines appropriate to the environment the foal will be exposed to once born. It is a miracle to me, as many times as I have seen it. I know it is science, but I feel the presence of God in the stable when a foal is born and receives its first blessing from the miracle of collustrum.