Together, we will explore:

• what equine connective tissue is and its different categories and sub-categories. 
• functions of connective tissue, what it is made of, and where it can be found in your horse.
• its importance and the benefit it can bring when functioning properly.
• what can happen when it is subject to disease and disorders and the impact this can have on your horse, with a nod to the human impact also.
• some tips on what you can do to help keep your horse’s connective tissue system healthy.

The horse has four basic kinds of tissue:

1. Nervous tissue (as found in the brain, spinal cord, and nerves).
2. Muscular tissue (as found in skeletal, cardiac, and smooth muscle).
3. Epithelial tissue (as found in skin, lining of intestines, and lining of the respiratory tract).
4. Connective tissue (as found between other tissues everywhere in the body).

Connective tissue is our focus here and is the most abundant, widely distributed, and varied type of body tissue. Whilst diverse, they do share multiple structural and functional features which brings them together under the term “connective tissue”.

Equine connective tissue binds the horse’s body together, connects to other tissues and provides support. This means it provides a range of essential and specialist roles in many locations throughout your horse.

The three components of connective tissue are cells, ground substance and fibres, with the latter two making up what is termed the extra cellular matrix (ECM). Refer to Table 1 for a further overview of these components.

Main Categories of Connective Tissue

The two main categories of equine connective tissue are Connective Tissue Proper and Specialised Connective Tissue, each of which then have their own sub-categories. Refer to Diagram A to help illustrate.

Connective tissue proper: 

– Loose

– Dense

Specialised connective tissue:

– Cartilage

– Bone

– Blood and Lymph

– Adipose

– Reticular

So, let’s look at each of these categories in more detail:

Equine connective tissue proper

Connective tissue proper  helps connect tendons, ligaments, muscles, skin, and bone. It is sub-categorised into loose and dense tissues.  

a) Loose

Loose, or areolar, tissue:

• holds organs, anatomic structures, and tissues in place.
• is made up of collagen fibres loosely scattered in the ECM.

An example of loose connective tissue is lamina propria. Lamina propria is found beneath the epithelium of mucosal membranes, such as that of the intestinal and respiratory tracts. 

b) Dense

Collagen fibres heavily packed in the ECM either in parallel order (dense regular), or randomly interlaced (dense irregular), or elastic:

1. Dense Regular (in parallel order), such as that of tendons, ligaments, and deep fascia.
2. Dense Irregular (randomly interlaced), such as that of the pericardium in the heart.
3. Elastic, such as that of arteries.

Specialised equine connective tissues

Specialised connective tissues are composed of various specialised cells and ground substance. These diverse but specialised connective tissues include cartilage, bone, blood, lymph, adipose and reticular tissues.

a) Horse cartilage

Cartilage provides protection, flexibility, cushioning, and support.

Chondroblasts cells make up cartilage and secrete a matrix composed of collagen, elastic fibres and glycosaminoglycans. These cells mature into chondrocytes, which make up the cellular component of cartilage. Cartilage acts as a shock absorber and reduces friction to protect the horse’s joints and bones.

Fibre types found in cartilage are Collagen II (hyaline cartilage), Elastic Fibres (elastic cartilage), and Collagen I (fibrocartilage).

Examples of where cartilage can be found are in:

1. Knee joints.
2. Ribs.
3. Stifle joints.
4. Between the vertebrae of the horse’s spine.
5. Hock joints.

b) Equine bone

Bone is specialized for structure, support, and protection of organs. It is made up of osteocytes, which secrete a hard mineralized matrix. The hard exterior surrounds a softer bone marrow interior, which houses stem cells that produce blood cells for the horse. Osteoblasts and osteoclasts are special cells that help horse’s bones grow and develop. Osteoblasts form new bones and add growth to existing bone tissue. Osteoclasts dissolve old and damaged bone tissue, meaning it can be replaced with new, healthier cells created by osteoblasts.

The skeleton of the horse includes, but is not limited, to the following bones by way of examples:

1. Cannon bones.
2. Skull.
3. Vertebrae.
4. Sesamoid bones.
5. Navicular bone.

c) Blood and Lymph

Blood and lymph connect all systems of the horse’s body.

Blood:

• transports oxygen, nutrients, and wastes.
• helps regulate body temperature.
• plays a significant role in fluid and electrolyte balance.
• has a protection function due to clotting of wounds to prevent blood loss, helping against microorganism invasion (e.g., white blood cells) and disease prevention (e.g., antibodies).

In addition, Lymph maintains fluid levels, transports substances, and participates in the immune response.

d) Adipose tissue

Adipose tissue is well known for fat storage, which involves cells called white adipocytes. Adipose tissue has a thermoregulation role but, as horses only have low quantities of the brown adipocyte cells linked to this, it is not a well documented area. However, an evolving area of research is the role of adipose tissue as an endocrine organ, which will be interesting to track for horses with obesity.

e) Reticular tissue

Reticular tissue has a branched, mesh-like pattern (often called reticulum) due to the arrangement of reticular fibres (reticulin). These are  Type III Collagen Fibrils organised in delicate networks. You can find reticular tissue in highly cellular locations, such as the liver.

Connective Tissue Disease and Disorder

Whilst muscle and neural tissue topics may be more familiar to many, connective tissue has the important function of ensuring all the other body systems work in harmony. Meaning that healthy connective tissue allows for more harmony throughout the horse. Whereas, when connective tissue is subject to disease or disorder the balance of harmony is disrupted. As a result, a rider (or trainer) may feel that something isn’t quite right in the horse’s way of going.

Examples of connective tissue diseases and disorders in the horse include but are not limited to:

• Osteoarthritis / Degenerative Joint Disease (DJD).
• Sidebone.
• Bucked (sore) shins.
• Splints.
• Chip fragments of bone and cartilage.
• Fractures.
• Tendon injuries.
• Ligament injuries.
• Tendon inflammation.
• Ligament inflammation.
• Degenerative Suspensory Ligament Desmitis / Equine Systemic Proteoglycan Accumulation (ESPA)
• Osteochondritis dissecans.
• Sacro-iliac disease.
• Fascia adhesions.

The impact of which to the horse can range across, depending upon the nature of the issue:

• Horse lameness.
• Changes in horse behaviour.
• Pain and welfare concerns.
• Reduced range of motion.
• The need for corrective shoeing and trimming.
• Postural issues.
• Gait restrictions and abnormalities.
• Compensatory issues.
• Poor performance.
• Decreased quality of life.
• Proprioception challenges.

Consequently, there can be a human impact of:

• Increased veterinary, farrier, medicine, and care costs.
• Loss of training time for horse and rider.
• Missed qualifications.
• Missed competitions for the horse and rider combination / horse owner.
• Confusion and frustration in trying to determine a root cause.
• Stress and upset.

Therefore, the benefits of looking after your horse’s connective tissues are as plentiful as the types of connective tissues themselves.

Opportunities to care for them (for non-inherited connective tissue scenarios) include, in no particular order:

• Preventing exposure of your horse to toxins.
• Providing an appropriate exercise program, with sufficient warm up and cool down periods.
• Avoiding long periods of stable confinement.
• Giving access to turn out for freedom of movement.
• Engaging professionally qualified equine care services for your horse when needed (e.g., equine vet, farrier, horse chiropractor, equine behaviourist).
• Using well fitting tack (e.g., saddle, bridle, girth etc.).
• Carrying out appropriate stretching techniques.
• Keeping your horse well hydrated.
• Not using training gadgets that may cause harm.
• Continually improving your riding technique with the use of an experienced / qualified coach.
• Expanding your knowledge of connective tissues.
• Ensuring quality nutrition tailored to the needs of the horse.

Horses in training and competition, as well as leisure horses, invariably face stressors such as:

• increased stable confinement.
• reduction in pasture turn-out.
• increased exercise intensity.
• travel.
• competition venue stabling.
• A heightened risk of exposure to pathogens (disease-causing organisms).

These stressors tax the connective tissue system of the horse, meaning a horse can no doubt benefit from additional support.

Feel the difference.

The CONNEXION formulation is for nutritional support of the connective tissues of the horse. You can find it online for your horse via the shop page: CONNEXION® – Equine-X

Some additional interesting reading and resources you may want to check out are:

A 3D poster of the hoof palmar systems, showing bones, ligaments and tendons from The Equine Documentalist (T.E.D.): https://www.theequinedocumentalist.com/product-page/ligaments-and-tendons-3d-digit

Understanding the role of Adipose Tissue as an endocrine organ with a central role in obesity pathology is an emerging area. This British Equine Veterinary Association (BEVA) article may be of interest: Bringing equine adipose tissue into focus – McCullagh – Equine Veterinary Education – Wiley Online Library

A quick read on fascia and equine health: Fascia and Equine Health: An Integral Connection – GRASSROOTS GAZETTE (thegrassrootsgazette.ie)