A balanced feeding program is key for yearling horses, as it sets the foundation for their growth and development into adulthood. Yearlings are transitioning from foals to young horses, and their nutritional needs are unique during this stage of life.

Yearlings require higher energy and protein levels compared to mature horses to support healthy growth and muscle development. They also need a balanced intake of essential vitamins and minerals, like calcium and phosphorus, for sound bone development.

The best way to meet these needs is with good quality forage and appropriate supplementation. Adding alfalfa hay and/or soybean meal is often sufficient to meet the increased protein needs of yearlings. Feeding a balanced vitamin and mineral supplement can also help to avoid nutrient deficiencies that can impair growth.

For additional support, you can consult with an equine nutritionist to ensure your horse’s diet is well-balanced. Working with a qualified nutrition is especially important if you plan to develop your yearling for athletic disciplines, helping to set them up for success in the performance arena.

Growth in Yearling Horses

Horses between the ages of 12 and 23 months old are called ‘yearlings’, and those that are 18 months and older are often referred to as ‘long yearlings’.

During this stage of life, yearlings undergo rapid growth, with noticeable changes in height and body proportions. Regularly monitoring your yearling’s growth rate is critical for supporting their overall health and future performance goals.

Growing too slow can result in failure to achieve their optimal mature size, whereas growing too fast increases the risk of developmental orthopedic diseases and joint issues in later life. [2]

Yearlings typically reach 65% of their mature weight by one year old, and 80% of their mature weight by 18 months old. [2] For a growing horse that is expected to reach a mature weight of 1,100 lbs (500 kg), this equates to:

  • 12 months old: 715 lbs (325 kg)
  • 18 months old: 880 lbs (400 kg)

Consider the breed of the yearling’s sire and dam to estimate their mature weight.

Growth Rate

Your yearling’s growth rate depends largely on their genetics, feeding program, and level of exercise. [2] Foals grow most rapidly during the first few months of life, and their growth rate slows down towards their yearling year and beyond.

This is not a linear decline, but resembles a wave pattern that is influenced by external factors such as: [2]

  • Length of Day
  • Temperature
  • Forage availability

Smooth Growth Rate

The goal of feeding programs for yearlings is to achieve a smooth rate of gain throughout the growth phase. Periods of suboptimal nutrition can temporarily slow down the growth rate due to nutrient restriction.

When nutrition is improved, periods of more rapid growth can follow, known as compensatory gain. [2] While compensatory growth can effectively get a horse caught up in terms of overall body size and weight, it may not result in uniform skeletal development. This can lead to orthopedic issues, including developmental orthopedic diseases (DOD).

When formulating diets for yearlings, we aim to avoid or minimize compensatory gain to promote long-term soundness. This can be accomplished by adjusting the diet in response to forage quality and availability to provide consistent nutrition.

Average Daily Gain (ADG) for Yearling Horses

Mature Weight 12 Months Old 18 Months Old
400 kg (880 lb) 0.36 kg (0.79 lb) 0.23 kg (0.51 lb)
500 kg (1100 lb) 0.45 kg (1 lb) 0.29 kg (0.64 lb)
600 kg (1320 lb) 0.54 kg (1.2 lb) 0.34 kg (0.75 lb)


Average Daily Gain Calculator

Enter your horse’s predicted mature weight and their current age in months below to calculate their expected Average Daily Gain (ADG).

Calculate Average Daily Gain (ADG)


Average Daily Gain:


This calculator estimates your yearling’s average daily gain using the following equation, where M is the predicted mature body weight (kg) and A is the yearling’s age in months: [3]

ADG (kg) = M x 6.97 x (e(-0.0772xA))/3040

Monitoring Growth

To effectively monitor your horse’s growth rate, you can use the following measures:

  • Body weight
  • Wither height
  • Hip height
  • Body length
  • Heart girth

At a minimum, body weight and wither height should be regularly measured using a scale and weight tape. Record these measures over time to inform feeding decisions, particularly in situations where growth rate needs to be limited or increased.