OCD AND NUTRITION FOR YOUNG HORSES: Latest Findings

Intro:

At the KER Equine nutrition conference in Lexington KY May 1st, Dr Joe Pagan presented some very interesting findings into the possible causes of DOD and its relationship with nutrition.

Development Orthopedic Disease (DOD) is a term that encompasses a group of conditions that affect young horses. These include Physitis (often mistakenly called Epiphysitis), Osteochondrosis, Osteochondritis Dissecans (OCD). Wobbler Syndrome, and acquired flexor deformities. It used to thought that these were caused by imbalance or deficiencies in mineral nutrition, and yet even when the mineral status of young growing horses was drastically improved the condition, though it got less frequent did not go away.

In 1994 Glade et al., and in 1995, Sarah Ralston of Rutgers University implicated high blood glucose and the corresponding insulin response to incidence of OCD. Following up on this research, KER presented at the 2001 conference a paper on incidence of OCD and Glycemic Response in Thoroughbred yearlings.

Background:

Firstly a little background.

How bones grow: The long bones of the skeleton grow by first forming a kind of cartilage, then the cartilage changes in nature (matures) by forming a collagen protein matrix into which minerals are deposited to form the crystalline structure of bone.

The growth of the cartilage is controlled by growth hormone and is genetically determined. The collagen matrix has to strengthen itself by forming cross linkages, and this cross-linking involves an enzyme, which contains copper ions. It has been shown that very high levels of zinc, phosphorus or energy can interfere in this process. Low copper levels also interfere with this step.

After the collagen matrix has been produced it has to mature before it can be mineralized. This maturation process is controlled by thyroid hormone, thus in hypothyroid foals bone maturation is impaired.

Once the collagen has matured, it is mineralized. For this process Calcium, Magnesium, Phosphorus & Vitamin D (Cholecalciferol) are all required if varying amounts. Very high levels of one mineral may interfere with the use of the others hence very high phosphorus will interfere with calcium and may cause a mal-formation of the bone. Low calcium levels will also cause malformation.

As the bone becomes mineralized it does so in a pattern of where the cells surrounding the blood vessels into the cartilage become ossified first. If there are insufficient blood vessel going into the cartilage then there will areas of insufficient ossification, called osteochondral lesions (OCD lesions).

Osteochondral lesions can occur in two ways.

The first reason is when the matrix fails to form properly, and hence cannot support the normal formation of bone. This may have a nutritional cause such as copper deficiency, excess energy intake, and calcium or phosphorus imbalance.
Also problems with the amounts of growth hormone or thyroid hormone may be involved here.

The second reason for osteochondral lesions may be if the normal blood supply to the growing cartilage is impaired. If the nutrient supply is interrupted proper bone formation may not occur.

A paper in 1997 by Henderson et al., on the effects of insulin and insulin-like growth factors on the growth of fetal and neonatal chondrocytes, showed that insulin affected the maturation of the cartilage at the pre-mineralization stage.

Carbohydrate digestion and Glycemic response

Carbohydrates occur in feed stuffs in several forms the simplest of these are the sugars and starches. Sugars and starches are digested and absorbed in the small intestine and are referred to as NSC (Non Structural Carbohydrates) as the sugars are absorbed across the small intestine wall the amount in the blood stream (blood sugar) goes up. As the blood sugar rises, the body releases insulin from the pancreas. The insulin controls the amount of sugar in the bloodstream by causing the various cells of the body to absorb it and to store it. Thus the rise in blood sugar is followed shortly by a rise in insulin levels.

The glycemic response is a measure of how much the blood sugar rises in response to a meal, and thus an indicator of how much of that feedstuff is NSC. IF one takes a known foodstuff as a baseline and calls it 100 then by comparing all the other feeds to this, it is possible to calculate a Glycemic Index, EG. How much (or little) a feed will raise the blood sugar as compared to the baseline feed. In horses the baseline feed in usually whole oats.

Part of a KER study was to make a glycemic index for several common horse feeds. Most glycemic indices used in the past were based on human studies and thus not always applicable to horses, which not only digest a little differently but also eat very different feeds.

Glycemic Response of some common horse feeds:

Whole Oats 100
Sugar Beet (hydrated) 72.2
SB rinsed 34.1
Dry SB w molasses 94.8
Corn 104
Sweet Feed 107
Alfalfa 52
Sweet Feed w/oil 52
Timothy Hay 32

An important observation done here is that forages, hay, old grass (not new spring grass) alfalfa etc do not have high glycemic indices, e.g. they don't raise the blood sugar much.

Another important point is that in the KER study addition of fat to a grain ration lowered the glycemic response. So the same amount of sugar was slowed in digestion by addition of fat.

KER recently did a large study of TB weanling/yearlings, looking at their response to carbohydrate feeding (Oral glucose tolerance test) and incidence of OCD. They also tested the Glycemic response to the feeds being used at the various farms in the study, using mature horses at their own research facility (see earlier).

In this study they compared the glycemic response of the yearlings to a meal and compared that with the incidence of OCD. They also compared incidence of OCD to bodyweight and to body scores of the weanlings.

On a farm by farm basis, they found considerable difference in incidence of OCD, one farm having zero cases and one farm 33% OCD.
They also found a very high correlation between yearlings with a high glucose (and hence insulin) response and incidence of OCD.
There was a high correlation between each farms mean (average of all the yearlings) glycemic response and the farms incidence of OCD. There was also a high correlation between the GI (Glycemic Index) of the farms feed (as measured on KER's own horses) and the incidence of OCD.
There was also a high correlation between the body score of the yearlings and incidence of OCD.

What does all this mean?

Bottom line appears to be; Feed feeds that have a low glycemic index to weanlings and yearling that might be at risk of OCD. This in a practical sense means forages, or feeds based on forages, minimal grain. If grain has to fed, take advantage of the effect of added fat in lowering GI, and add oil to the feed.

Keep the babies lean! Remember that body score index!
Keep the minerals up and balanced and keep the carbs low.

No doubt even as we speak/write the nutrition companies are hard at work formulating rations low in glycemic index for growing babies, but until they have them ready for the market, stay away from high GI feeds for your babies.


A number of companies now offer 'forage balancers' a low volume feed designed to fed with hay only, which supplies all the protein, minerals and vitamins that hay may lack. It might be wise to switch the babies and the pregnant broodmares over to a diet based on forages with a balancer like LinGro.

Dr. Melyni Worth Ph.D. - 2006 (c)

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