• Sara Lasseter

Development Phases of Foals and Young Horses

There are 4 factors to development in a horse:

1. Genetics

2. Environment

3. Management

4. Nutrition

We’ve listed this timeline of the development process so you can see how the 4 factors play a role during certain phases of development.


First 24 hours:

· Standing within 1-2 hours.

· Nursing within 2 hours after standing.

· Within 24 hours the gut “closes” to large molecules, which is what makes the need for colostrum so important during that time frame.

· Passes first manure (meconium) shortly after nursing.

· At birth, the coffin bone is the only bone fused, the remainder will take up to 6 years.

· Within 24 hours we recommend having your foal check done and dipping the umbilical stump in chlorhexidine at a 1:4 ratio. A vet check will usually include checking IgG levels to verify good colostrum intake, checking the mare for placenta passing, milk production, and checking the foal over for any abnormalities or deformities.


First week:

· Body is trying to regulate respiration, circulation, and digestion.

· Acclimating to fluctuations in light, temperature, and sound.

· Nurses two to three times per hour.

· Spends about 1/3 of the day resting usually on their sternum or side.

· Will start to wander further from mom, breaking into first canter around day 2 or 3.

· Should be gaining 1 to 3 lbs. per day

· Cannot regulate body temperature as well as an adult horse, in extreme weather make sure foal has shelter.


First Month (Dependence Period):

· Dependent on the mare for nourishment and protection.

· Has little to moderate interaction with other members of the herd.

· Most play is with the mare, playing with her tail, mane, ears, and halter.

· At 10-14 days will start to pick at mare’s feed and hay.

· Coprophagy of mother’s feces is normal at this age and provides essential nutrients.

· Flehmen happens about once an hour for colts and about once every 5 hours for fillies. Usually driven by urination from one of the herd mares.

· Have a farrier check your foal’s feet and limb conformation (hoof trimming will usually begin at 6-8 months.)


Month 2 to 3 (Socialization Period):

· Will begin to explore and leave mare’s side. Investigating the rest of the herd and creating play groups with other foals.

· By 8 to 12 weeks mare’s milk is no longer an adequate nutrition supply alone.

· Will begin learning social and behavioral lessons from herd society. For example, often kicked and not played with for a while, colts will learn quickly playing too hard is not acceptable. Mares or other adult horses who get pestered will correct young foals.

· Play increases: Fillies will tend to run, buck, and jump while colts instinctively tend to develop more combat skills in their play.

· Coprophagy and Flehmen continue during this time.

· Allogrooming (mutual grooming) peaks during this age. Fillies will allogroom about twice as much as colts.

· Time to begin a deworming schedule depending on your current program or the program your vet recommends.


Month 4 (Stabilization and Developing Independence Period):

· Increase in adult behaviors and a decrease in foal mannerisms and behavior.

· Nursing will happen about 1 to 2 times per hour, however, the amount of nutrients received are small at this point.


Month 6 to 12:

· Environmental transition into maturity begins at weaning.

· Reach approximately 46% of mature weight by 6 months, 65% by 12 months.

· Reach approximately 84% of mature height by 6 months, 94% by 12 months.

· Most lower limb growth is complete by 12 months.

· Long pastern bone fuse by 6 months, the hock by 12 months.

· Vaccination schedule should begin between 4 and 6 months depending on mare’s vaccination during third trimester.

· Check teeth every 6 months during the next two years as teeth are changing frequently, looking for retained caps, sharp points.

· Begin a farrier schedule if you haven’t already. Even if a young horse is not in training, regular trimming will help bones and hooves grow and form correctly and can often help correct any deformities if caught early on.

Months 12 to 18:

· From weaning to 2 years a foal will nearly double its weight. Nutrition and environment are critical to bone, muscle, and mass development during this time.

· Cannon bone fuse by 18 months.

· Yearlings go through a lot of growth spurts and hormone changes like teenagers. They can look gangly and drive you mad but don’t give up on them, it doesn’t last forever.


Months 18 to 24:

· Reached approximately 97% of mature height by 22 months.

· Reached approximately 90% of mature weight by 22 months.

· The knee bone fuse between 18 months and 2 ½ years.

This graphic, created by Naomi Tavian (@equinaomi), is a great image illustrating how long it takes for a horse to become fully mature — essentially not until they are six.


Other Milestones:

· Fully grown and physically mature at 4 to 6 years.

· Emotional maturity about 5 to 7 years.

· Between birth and 6 years a horse will erupt / develop 60 to 64 teeth. With the Deciduous (baby) set coming in during the first 9 months and the permanent set coming in from 12 months to 6 years.

· Bottom of Radius-Ulna fuse at 2 to 2 ½ years.

· Tibia and top of Radius fuse at 2 ½ to 3 years.

· Femur and Humerus fuse at 3 to 3 ½ years.

· The Scapula and Pelvis fuse at 3 to 4 years.

· The vertebrae fuse between 3 ½ and 6 years.


This is a good guide packed with information we have pulled from several medical journals, articles, and veterinarians, please remember these are suggestions only and no foal is exactly the same. Larger breeds develop differently than smaller breeds, and so on. There is also a long list of factors, conditions, and genetics that can change these phases and patterns. Please contact your veterinarian if you have any concerns or questions about the development of your foal.

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