Lots of important points around this topic - and lots of different ideas about what to do and what works! And, there are many different diets and ways of feeding that work well, if the fundamentals are covered.

For weanlings, the diet fundamentals are protein and minerals – the raw materials needed to build muscle, bone, blood cells – in fact, all the tissues in the body.Not to overuse the term, but the ‘fundamental’ consideration that needs to be foremost in our minds is soundness, so proper bone growth must be of paramount (and fundamental!!) importance.

The most important system at this age is the skeleton – more so than muscle development, body weight or size. This is because the musculoskeletal system doesn’t grow evenly – the skeleton grows first and then muscle is laid down, ie bone and muscle have their own windows of growth. The 3 periods of most rapid growth for bone are:

•         from 4 months before, until one month after birth

•         between 6-12 months of age – the weanling

•         just after puberty

On the other hand, maximum muscle growth - when the cells increase in size and number to their genetic potential – occurs between 2 and 24 months of age. These periods of intense growth are similar under different climatic conditions and the same pattern occurs regardless of breed.The second important consideration is that when growth rate is high, the risk of developmental abnormalities is high. Often not obvious until horses are in training, weaknesses and unsoundness in bones and joints develop primarily when horses are foals and weanlings!

The term ‘developmental orthopaedic disease’ (DOD) is used to describe any orthopaedic problem involving tendon, joint or bone tissue in growing horses - including osteochondrosis (OC), physitis, epiphysitis, angular limb deformities (ALD), flexural deformities (including contracted tendons) and wobbler disease.Achieving optimum growth requires thought and study so that genetic potential is reached without inducing bone diseases. Because of the link between above average weight gains and onset of bone diseases, weanlings should be kept in a lighter body condition. Muscle growth and fat (body condition) should not be allowed to get too forward while the bones and joints are vulnerable. A lighter, leaner weanling with appropriate height (remember height is an indication of bone growth, not muscle) is the ideal.

Whether a young horse develops muscle and bone or becomes too forward is determined by the quality and quantity of protein in the diet. The number of new cells the body builds – whether blood, muscle, bone or fat cells – depends on the amount and the amino acid profile of the protein in the diet. Most prepared feeds for growing horses contain 14-16% protein. But, horses don’t need a % protein, they need a number of grams of protein each day. For example, a horse fed 3kg of a 10% protein feed, or 1½ kg of a 20% protein feed gets 300g of protein in both cases.

Whether this protein is ‘useable’, depends on its amino acid profile. Proteins are made of chains of amino acids – good quality protein is high in essential amino acids. Of the 22 amino acids in nature, 10 are essential, cannot be synthesized in the body and must be provided by the diet. All the different feeds and all the different tissues in the body have their own formula or recipe of amino acids. Body building progresses until it runs out of amino acids – so a dietary deficiency of any single amino acid will limit new cell production – the remaining amino acids in the ‘recipe’ can’t be used . Unusable amino acids convert to fat. So % protein is not useful in terms of knowing how much usable protein the diet provides.

At no other age have we greater opportunity to guide growth and development. If nutrition is unbalanced or incorrect during these periods, the opportunity to achieve optimum muscle and bone development and to minimize the risk of future unsoundness, will be missed. As long as the diet meets amino acid requirements and doesn’t have too much energy, a strong, sound weanling will be the outcome – regardless of the feedstuff used.

EQUINE CLINICAL NUTRITION
Dr Jennifer Stewart