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Skeletal development of foals in utero & throughout growth

How early should we consider bone health?

It is never too early to start thinking about optimising the quality and strength of the young equine skeletal system as playing catch up with any aspect of development is not ideal. When in-utero, the skeleton develops as cartilage and is converted to bone gradually throughout pregnancy and also after the foal is born. In order to optimise bone development, it is important to consider how we can affect bone health through providing the correct nutrients to pregnant mares and also feeding our foals on the ground appropriately. Feeding adequate levels of vital nutrients is essential for bone development in any horse. However, one of the biggest challenges for breeders is trying to manage diet plans to avoid common problems associated with bone development in youngsters.

 What issues can occur that affect bone health?

As the youngster grows, the increase in bone size and bodyweight is coupled with increasing bone mineralization, muscle mass and the maturation of tendons, ligaments and cartilage. The delicate balance between bone development, muscle mass and bodyweight in these early years makes it one of the most common times for skeletal abnormalities to occur. These abnormalities are classified as Developmental Orthopaedic Disorders (DODs). DOD is an umbrella term used to describe a number of conditions associated with bone development in young, growing horses. The incidence, severity and treatment of DODs varies substantially and will most likely require veterinary and nutritional intervention.


Two commonly seen DOD conditions affecting youngstock are:

  • Physitis or epiphysitis: effusion around the knee and/or fetlocks, with or without associated pain, radiographs may be necessary. Treatment is often conservative and nutrition will play a key role
  • Osteochondrosis Dessicans (OCD): means the process of ossification is disrupted and damage to the cartilage occurs, the underlying bone is then vulnerable to further injury. Flaps of cartilage can become loose (dissected) and these will cause pain and inflammation around the affected joint as a result of excess fluid in the synovial space

Nutritional management is particularly important for any youngsters prone to or suffering with DODs. It is vital that these horses receive elevated levels of essential vitamins and minerals to aid their bone health.

Supplement to support bone health:

Cal-Gro is a pelleted supplement designed to support skeletal development in-utero and throughout growth. Therefore, Cal-Gro can be fed to either the pregnant mare, foal at foot or growing weanling/yearlings.  Cal-Gro contains specific ingredients to suit the needs of foals and youngsters in order to support that all-important bone development that everyone talks about so much.

Beneficial ingredients:

Calcium and phosphorus levels must be maintained within narrow limits for optimal bodily function. Therefore, when dietary intake is insufficient (which is likely in horses suffering with or prone to DODs), the body will draw upon its reservoirs to replenish these levels. This will essentially draw calcium from the bone to rectify the balance and as a result, the calcium levels within bone can fall below optimum and result in reduced bone density, bony malformations and vulnerability to fractures. To meet the carefully balanced requirements of calcium and phosphorus, it is advisable to supplement young, growing horses with an appropriate product such as Cal-Gro. Calcium and phosphorus are provided in the ideal ratio of 2:1 in Cal-Gro and is therefore beneficial in maintaining the correct balance of these minerals in the body. Vitamin D is also provided in Cal-Gro to help support the absorption of these minerals.

Silicon has also been demonstrated in research as having significant importance in skeletal health. Studies have shown that supplementation of silicon in the diet has resulted in decreased skeletal injuries and better training performance in young racehorses. Silicon also facilitates the absorption of various minerals and acts to enhance their activities within the body. Cal-Gro contains silicon to support bone, tendons and ligaments as they are put under additional stress when youngsters begin to load these structures. Loading these structures is initiated when foals are first turned out and continues as young horses are put into training and undergo stricter exercise regimes.

Copper and Zinc are also important mineral for bone, joint and connective tissue development. Feeding inadequate copper to the pregnant mare has been shown to increase the risk of DOD in the offspring, and unfortunately, supplementation of the foal after it is born does not mitigate this risk. Manganese is another mineral that has shown to be beneficial for bone health in horses as it is responsible for the synthesis of chondroitin sulphate, vital for healthy joints. Copper, zinc and manganese levels in forage, even lush spring grazing, are often inadequate to meet the young, growing horse’s requirements. Therefore, these minerals can be provided in the form of a suitable supplement such as Cal- Gro as it contains highly bioavailable sources of chelated copper, zinc and manganese.

Vitamin K plays a role in bone and cartilage metabolism and it is thought that deficiencies may affect bone metabolism. Whilst dietary requirements for vitamin K have not been fully established, there is evidence that vitamin K supplementation can be helpful for young horses, as it is necessary for the production of osteocalcin; the hormone responsible for facilitating bone metabolism and mineralisation.

Essential amino acids such as Lysine and Methionine have shown to play a key role in the development of strong, healthy bones and as they cannot be generated within the body, they must be provided to the horse in the diet. The inclusion of these amino acids in Cal-Gro helps to support collagen formation, a structural component of bone and therefore crucial aspect of healthy bone development.

The combination of ingredients in Cal-Gro gives owners and breeders the confidence that a well-formulated product can help support skeletal development for foals in-utero and and manage associated problems throughout their growth as they naturally undergo increased levels of exercise and enter training.

Want to know more about supplements that support skeletal growth and mobility? Speak with one of our equine nutrition experts.


O’Connor, C.I., et al., Mineral balance in horses fed two supplemental silicon sources. Journal of Animal Physiology and Animal Nutrition, 2007.

Logan AA, Nielsen BD. Training Young Horses: The Science behind the Benefits. Animals (Basel). 2021 Feb 9;11(2):463

Nielsen BD, Potter GD, Morris EL, Odom TW, Senor DM, Reynolds JA: Training distance to failure in young racing quarter horses fed sodium zeolite a. J Equine Vet Sci. 1993, 13: 562-567. 10.1016/S0737-0806(06)81526-1.

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