Heritability of temperament in horses

Is temperament mainly genetic or due to the environment? Before answering this question,
we should be clear about what is meant by ‘temperament’, says Dr Mac.

Heritability of temperament in horses
The Quarter Horse, traditionally used on cattle ranches, is known for its calm temperament. Photo: Dr Mac
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Both genetics (genotype) and the environment determine how a horse will look and behave (phenotype). Heritability is the proportion of the horse’s conformation and behaviour that results from its genotype. It is only three years since the genome of the horse was fully described, but the inheritance of colour is now well understood. The colour of a foal can be accurately predicted by knowing the colour of both its parents. By contrast, the heritability for temperament in horses is not as well understood.

Part of the reason is possibly that ‘temperament’ is not well defined. What a novice rider would consider to be ‘far too hot’ may be the kind of horse desired by an experienced rider. Arabian breeders breed for ‘presence’, while some riders may consider an Arabian with ‘presence’ to be a ‘spooky’ horse.

Is a horse that moves slowly and steadily ‘good- tempered’ or a ‘lazy slug’?

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Different findings
The heritability of temperament varies from below 1% to more than 60%, depending on which authority one reads; this is probably because different criteria are measured. The way a horse reacts to an unexpected noise or movement is one of these criteria. Would a horse react negatively to an unexpected stimulus by shying or by showing a startle reflex?

It was found that breeds with Arabian and English Thoroughbred bloodlines were the most reactive, while Fjord ponies and Quarter Horses were lowest on the breed reactivity scale. Temple Grandin, widely regarded as a guru on animal behaviour, states bluntly that fine-boned light horses with high heads are far more spooky than solidly built horses with low head carriage. This echoes the ancient classification of horses into ‘hot-blooded’ and ‘cold-blooded’ types.

Despite this, Arabian horses are very easy to break in, while warmbloods, which are far more stocky, often need a lot more work before they will carry a rider. Anxiety in horses is often correlated with wind sucking and cribbing, and researchers have found a high level of breed-related heritability, but anxiety is also known to be associated with high grain levels in the diet, so this result may be biased. British ponies hardly ever windsuck, but because they put on weight easily, they are seldom fed concentrates.

Cortisol and carbohydrates

Other researchers conducted an experiment on two sets of geldings used in a riding school environment that had been grouped as excitable or calm by experienced riders. The type of temperament in each group was measured by the cortisol level in the saliva and increased heart-rate. The calm group showed an increase in heart rate and cortisole only at feeding times.

Irrespective of the breed of horse, it has been confirmed that diets high in easily digested carbohydrates, such as maize, increase reactivity in horses. Underfed horses on low carbohydrate or unbalanced rations are calmer. Horses learn by imprinting and habituation. If a mare is handled gently and calmly when it has a foal at foot, the foal is likely to be easy to handle.

The question remains: can the pedigree of a horse reliably predict its temperament and are breeders able to breed horses with desirable temperaments?

The answer is yes. But as a purchaser, you should be sure that you and the seller mean the same thing when you talk about ‘temperament’.

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