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  Discussion on Influence of starch intake on skeletal development
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DrO

Posted on Tuesday, May 17, 2005 - 12:09 pm:

The idea that too much protein was largely responsible for developmental orthopedic problems was shot down in the 90's with a very large long term study that showed growing foals on a diet composed of 30% protein, but balanced to prevent excessive energy intake, did not effect their growth. More recently the idea of excessive intake of rapidly digestible carbohydrate was responsible for this and a host of problems in horses. As a result we have seen many prepared foal diets start to include higher fat contents. However, a brand new study does not support the idea. When large amounts of starch were added to the growing foals diet and compared with low starch diets that again were balanced for energy intake no difference was found in developmental bone defects. Interestingly was that the high starch diets seem to condition the growing horses system to better process glucose.


J Anim Sci. 2005 May;83(5):1033-43.
Influence of starch intake on growth and skeletal development of weanling horses.

Ott EA, Brown MP, Roberts GD, Kivipelto J.

Department of Animal Sciences, University of Florida, Gainesville, 32611-0910, USA.

Forty-four weanling horses were used in two experiments to evaluate the effect of starch intake on growth and skeletal development. In Exp. 1, the weanlings were fed either a grain-based, high-starch (31.1%, DM basis) concentrate or a by-product-based, low-starch (0.0%) concentrate with coastal bermudagrass (Cynodon dactylon) hay. Corn oil was used to equalize the energy concentration of the concentrates. The concentrate:hay ratio was 64:36 (as-fed basis), and intake was the same for both diets. Body weight gains were greater by the weanlings consuming the high-starch concentrate (0.81 vs. 0.67 kg/d; P = 0.01). Total body length gain also was greater for the weanlings consuming the high-starch concentrate (15.5 vs. 13.2 cm; P = 0.045). Other body measurements and bone mineral deposition were not influenced by diet or gender. At the end of the experiment, postprandial blood glucose concentrations suggested that the horses on the low-starch diet were less efficient in metabolizing blood glucose than were those that had been consuming the high-starch diets. In Exp. 2, the weanlings were fed either a high-starch (34.7%) or medium-starch (17.0%) concentrate plus coastal bermudagrass hay. Corn oil again was used to equalize the energy content of the medium-starch concentrate to that of the high-starch concentrate. The concentrate:hay ratio was 64:36 (as-fed basis), and the intake was the same for both diets. The diets did not influence rate of gain (0.75 kg/d; P = 0.98), body measurements (P = 0.11 to 0.93), or bone mineral deposition (P = 0.66). Animals on the medium-starch diet tended to have blood glucose concentrations that peaked earlier and were lower at later times than those consuming the high-starch concentrate. Bone osteochonDrOtic lesions were not related to the diet and were found to decrease during the course of the experiment for both the high-starch and the medium-starch diets (P = 0.006 and 0.016, respectively).

The mechanism by which naturally occuring OCD develops still remains a mystery. We know that mineral deficiencies and imbalances can cause it, but is this happening in our horses at pasture? Still there seems to be a high correlation of rapidly growing foals and clinically significant OCD. Recent work on the importance of stress in remodeling joint cartilage in foals strongly suggests that rapid changes in exercise level may also be responsible for some OCD lesions. Our best protection still seems to be keep the growing foals slightly ribby with well balanced feeds and allow plenty of free choice exercise. The nutritional goals might be a bit more difficult with the higher energy density of some of the new high fat foal feeds.
DrO
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