What is colostrum and why is it so important?

Colostrum is also called “first milk”, as it is the first milk produced in the mammary glands of a pregnant mammal, including both humans and horses. It appears thick and yellowish and is high in proteins and antibodies to help boost the newborn’s immune system. Colostrum is produced in the days leading up to birth and can sometimes be seen dripping and “waxing” on the teat ends just before a mare gives birth. After the birth and for the rest of the time nursing, the mammary glands produce what we think of as normal milk: full of nutrition, but lacking any antibodies.

This wild filly will deliver her first foal within the next 24 to 48 hours. Notice the ‘wax’ at the end of each teat.

In humans, most people recommend breastfeeding as the healthiest option for a newborn baby, especially in the first few days to make sure the baby gets the colostrum. However, when breastfeeding isn’t an option there are plenty of supplemental formulas which will provide the baby with the proper nutrition.

In horses, this is not quite the case. It is much more crucial that a newborn foal gets colostrum than a newborn human. All due to one little difference between the placentas! The mammalian placenta is basically a food sac for the developing fetus attached by the umbilical cord, through which the mother’s body passes nutrients and out of which the fetus eliminates waste. The mother and the fetus both have arteries that bring blood to the placenta, though their blood streams don’t actually mingle. The arteries of a human mother get close enough to the fetus to allow the passage of antibodies from her blood to the developing fetus. However, the placenta of horses has three extra layers of tissue in between the arteries of the mother and the fetus. These allow for nutrient exchange but are too thick for larger structures like antibodies to pass through. So a foal is born without any antibodies prepared against infection, while human babies are born with protection in the form of their mother’s ready-made antibodies. The only way for the foal to receive its mother’s antibodies is from the colostrum.

Why do new foals need antibodies?

Birth is a traumatic event for the newborn in many ways. It suddenly exposes a body to new sensations and external forces, including any bacteria present in the surroundings. Healthy foals are born with a functional but not yet fully developed immune system. Without antibodies already in place it can take several days after a bacterial infection for the adaptive immune response to kick in and produce enough of its own antibodies to combat the infection.

Almost all foals are exposed to a bacterial infection in their first few days of life. Foals that do receive their mothers’ antibodies from colostrum still often develop diarrhea (called “foal heat diarrhea” because of the timing), but the infection can prove fatal for foals without enough ready-made antibodies. In one study (1) researchers tested the success of newborn foals who received colostrum versus newborn foals who did not. Of the colostrum deprived foals, 7 out of 8 developed septicemia, a serious infection where bacteria enters the bloodstream. Even with intense veterinary treatment only 3 of the foals survived. Of the six foals in the control group which did receive colostrum, none developed septicemia, only one developed diarrhea, and all survived. So clearly the benefits of colostrum are very important for the new foal!

Why is the timing of receiving colostrum so important?

There is yet another complication beyond just drinking the colostrum. Remember when we said that antibodies are too large to pass through the membranes of the horse placenta? Turns out they are also too large to pass through the walls of the intestines where other nutrients are absorbed. But horses have evolved a solution for this. When a foal is first born its intestinal walls are lined with specialized cells that are able to absorb the antibodies and transfer them to the bloodstream. However, the presence of these cells is extremely time limited. The highest absorption efficiency occurs within 8 hours of birth, and even 3 hours after birth the absorption efficiency has drastically dropped. By 24 hours after birth these cells are almost entirely gone. This means that a foal needs to drink as much colostrum as it can within the first few hours after birth, otherwise the benefits are lost.

Up Next – Part III

How is the situation different for a wild foal versus a domestic foal?

A huge thank you to the author of Neonatal Foal Survival, Melissa Thompson! Her expertise, thought, and dedication is beyond inspiring!

References and further reading for Part I:

1 A prospective study of septicaemia in colostrum-deprived foals. Julie A. Robinson, G. K. Allen, Eleanor M. Green, W. H. Fales, W. E. Loch and Christina G. Wilkerson. Equine Vet. J. (1993) 25 (3), 214-219. https://www.ncbi.nlm.nih.gov/pubmed/8508750