Equine Fetal Development Stages Explained!

Last Updated on November 18, 2022

The equine fetal development stages are a fascinating topic, as we now understand a lot more about what occurs throughout the pregnancy of a mare. Let’s find out everything you need to know about the horse fetus stages!

What Are The Equine Fetal Development Stages?

When a mare is pregnant, she carries a fetus in her uterus that grows from just a cluster of cells into a healthy foal. Different organs and body parts form at certain horse fetus development stages, and the foal will grow at different rates according to how far along the pregnancy is.

The gestation period of a horse lasts for an average of 11 months, and the horse fetus stages can be split into three main sections:

First Trimester – Equine Fetal Development Stages

The first trimester consists of the first three months of pregnancy in a mare following a successful conception. For the first 40 days, the growing foal is referred to as an embryo, as it is a growing collection of cells. Following this, it becomes a fetus.

First Trimester - Equine Fetal Development Stages

Here are some key equine fetal development stages that occur during the first trimester of pregnancy:

Month 1

The embryo grows to the size of a pea during the first month of pregnancy. For the first 16 days, it moves freely around the uterus, and following this, it settles in place. A heartbeat is detectable by the 24th day of pregnancy, and the basic body structures are also developed by this point.

Month 2

During this month the fetus grows to the size of a caterpillar and starts to develop facial features. The elbow and stifle joints become more defined.

Month 3

In the final month of the first trimester, the fetus grows to the size of a chipmunk. Hooves start developing and the fetus becomes much more active.

Second Trimester – Equine Fetal Development Stages

The second trimester consists of the fourth to seventh months of an equine pregnancy. At the start of this stage, the mare will not look obviously pregnant, as the fetus is still relatively small. During the seventh month the growth rate increases, in preparation for a big growth spurt during the third trimester.

Month 4

During the first month of the second trimester, the fetus will grow to the size of a kitten. Fine hairs start to grow on the face of the foal, particularly around the muzzle. The foal is still quite active, but its movements are more confined as space becomes restricted.

Month 5

The foal grows to the size of a rabbit and develops clearly visible eyelashes. It now fills a large part of the sac in which it grows, restricting movement still further.

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Month 6

By the end of the sixth month of pregnancy, the developing foal is the same size as a groundhog. The mane and tail start to develop.

Month 7

During the final month of the second trimester, the foal grows to the size of a raccoon. The mane and tail are clearly visible, and the foal’s position changes in preparation for the rapid growth during the final trimester.

Third Trimester – Equine Fetal Development Stages

In the third trimester, the growth rate of the foal accelerates rapidly, and the mare’s nutritional needs will increase as a result of this. She will need higher protein levels to meet the demands of the growing foal. The mare will also start to look obviously pregnant, with an enlarged abdomen.

Month 8

In the first month of the final trimester, the foal grows to the size of a Beagle. It will develop more hairs on the face, poll, muzzle, and throat.

Month 9

This is a month of rapid growth, where the foal gains around one pound in weight every day! By the end of month 9, the foal will be the size of a Dalmatian. Longer mane and tail hair will be visible at this stage.

Month 10

The foal is getting very large at this stage and will be around the size of a newborn Jersey calf by the end of month 10. The hooves will have extended to the tip of the uterine horn.

Month 11

This is it – the final month of pregnancy! By the end of month 11, the fetus will have grown to the size of a newborn foal, and its body systems and internal organs will be fully prepared to survive in the outside world. The foal may roll and turn during this final month, in an effort to get in the correct position for birth.

When Does Foal Turn Before Birth?

Once the foal is fully formed, it needs to move into position for delivery. During the final trimester, the foal is normally positioned on its back, and it needs to roll over in order to exit the birth canal successfully. It will move around considerably during the final month of pregnancy, but the final positioning takes place during the first stage of labor.

At this point, the foal will extend the head and front limbs towards the birth canal, which has been in a flexed position up to this point. The foal will then rotate its body, taking it from lying on its back to becoming the right way round. The foal should end up in a diving position, with the head and forelimbs ready to exit via the birthing canal first.

As this turning often takes place just before birth, it can be very difficult for veterinarians to assess if a foal is in the right position for delivery. This is why it is important to be vigilant when a mare is foaling so that any issues can be quickly corrected.

Summary – Equine Fetal Development Stages

So, as we have learned, there are several important equine fetal development stages. These are split into three trimesters, with a total pregnancy period of 11 months. The foal grows slowly during the first two trimesters, with a period of rapid growth during the final trimester in preparation for birth.

We’d love to hear your thoughts on the key equine fetal development stages! Do you have a mare that is in foal and you are wondering at what stage her fetus is at? Or maybe you’ve got some questions about monthly foal development in the womb? Leave a comment below and we will get back to you!