The ideal time to transition a younger horse to an adult horse feed depends on many factors. There needs to be a balance between ensuring your horse is receiving enough nutrients to support continued growth, while also ensuring that you are not overfeeding them. Once horses hit their second year of life, it is wise to monitor their growth and weight to ensure continued support. Generally, most young horses can transition from their growth-centered diets to their adult diets between their second and third year.

Horse Growth Explained

All horses go through spectacular growth in their first year of life, which continues into their two-year-old year. Most horses reach about 50% of their mature adult weight and 90% of their adult height by the end of their first year (12 months old).  By the end of their second year (24 months old), most horses will be about 90% of their mature body weight and 95% of their projected height. Factors that influence this are:

  • Genetics/Breed. Individuals within a breed may vary, but generally are similar. Due to selection for quicker growth, light horse breeds, like Thoroughbreds and American Quarter Horses, grow quicker than larger horse breeds like our draft horses.
  • Season. Foals born in the winter tend to initially grow slower than foals born in the spring. With spring grasses, winter-born foals catch up with growth spurts. Growth can slow in late summer and early fall due to poorer quality pastures.  
  • Exercise. For bone to grow properly, foals need exercise. Withholding exercise or keeping foals stalled for long periods can slow growth. Free-choice exercise is always recommended.
  • Nutrition. Foals and yearlings need careful dietary management to ensure proper growth. You can learn more HERE and HERE.

Once most horses reach their second year of life, they are considered “adolescents.” This is when their growth has slowed considerably. Slower growing breeds, like draft horses, may still experience some substantial growth spurts.

It is estimated most light horse breeds reach their full mature weight and height between 4 and 5 years old. This is when they are considered an adult and when most of their growth plates have fused and become bone. For slower growing horses, (i.e., draft breeds) this doesn’t happen until they are about 7 or 8 years old.

When to Transition the Adolescent Horse to an Adult Horse Feed

It does get confusing and somewhat tricky on the question of when to transition a young horse off its nutrient-dense growth feed to a more suitable and less nutrient-dense adult horse feed. The answer lies in the growth of that individual horse. How much have they already grown and how much growth will they experience over the coming two to three years? This means owners need to continue to monitor their young horses until they reach their optimal height and weight.

Nutrient requirements for an adolescent horse do differ from those of a fully mature horse.   Below are some of the nutrient requirements of a 2-year-old horse (weight 950 lb/430 kg) with light exercise compared to an idle, mature horse (weight 1100 lb/500 kg) provided by the National Research Council (NRC, 2007):

  • Energy: 21.8 Mcal/day versus 16.7 Mcal/day
  • Crude Protein: 11.3% of total diet versus 8.0% of total diet
  • Lysine (limiting amino acid): 35.7 grams/day versus 27.1 grams/day
  • Calcium: 36.7 grams/day versus 20 grams/day
  • Phosphorus: 20.4 grams/day versus 14.0 grams/day
  • Vitamin E: 858 IU/day versus 500 IU/day

Clearly, the NRC recommends more nutrients for two-year old horses compared to adult horses. However, the NRC does not specifically address nutrient requirements for 3- and 4-year-old horses. It can be assumed that a two-year old’s daily nutrient requirements gradually decline to match those of an idle, adult horse. Thus, during their second and into their third year of life, horses do need some extra nutritional support.

It is generally recommended that an adolescent horse that has reached 90% of its ideal weight and 95% of its ideal height can transition off a growth feed to an adult, mature horse feed. However, they will likely need extra nutrient support until they reach full maturity.

So, What Do You Feed the Adolescent Horse?

Once a horse reaches two-years of age, the best way to monitor their growth is through the Henneke Body Condition Scoring System.  Very similar to adult horses, the ideal body condition score for an adolescent horse is 5 to 6. Owners will also want to continue to monitor their young horse’s height and weight to evaluate when they reach their ideal size.

Generally, horses transitioning from a yearling to 2-year-old diet should be given access to quality pasture or provided a high-quality hay, either free-choice or at 2.5% of their body weight per day. You can also safely transition the young horse off a growth-specific feed, such as Growth Pellet, to a more appropriate feed formulated for adults, such as Kalm ‘N EZ® Pellet. It is always advised to follow the manufacturer’s feed recommendations or contact the feed manufacturer directly if you are unsure of feeding rates.

An example of an appropriate feed for an adolescent horse is Essential K®. This is a low NSC (non-structural carbohydrate), nutrient-dense feed. Feeding rates will vary based on weight, but assuming your adolescent horse will eventually be 1100 pounds, you could feed:

  • Young, growing horse (900 lb): 3 pounds of Essential K® per day.
  • Adolescent horse (950 lb): 2.5 to 3 pounds of Essential K® per day.
  • Adolescent horse (1000 lb): 2 to 2.5 pounds of Essential K® per day.
  • Adult (idle) mature horse (1100 lb): 1 to 2 pounds of Essential K® per day.

Of course, any adolescent horse that enters training or is being used as a breeding animal, their nutrient requirements will be higher than those recommended for a fully mature, adult horse. Even though they are under similar conditions, like exercise or breeding, our adolescent horses need extra support for continued growth. It is also worth noting that our slower growing horses may need to continue a growth feed through their third year of life.

Summary

When to transition your young horse to an adult horse diet depends on many variables. Much of it will boil down to that individual horse’s genetics. However, in broad terms, most two-year-olds that have reached 90% of their ideal weight and 95% of their ideal height can transition to diets more suitable for adult horses. However, they will need extra nutrient support until they reach 100% of their ideal weight and height. If you have questions or concerns, please contact us for a free, personalized feeding plan.

Chris Mortensen, Ph.D.