Can You Breed for Disposition?
By Dr. Jim and Lynda McCall
"That colt is just plain crazy!" Is it because he ran with a bad crowd? Was abused as a youngster? Had a poor home environment? Or was it because "the apple didn't fall far from the tree." This last statement is frequently used to explain human behavior but just how valid is it in a discussion about the temperament of horses.
Trying to identify the nature of a horse is not a simple task. Its disposition is a composite of traits. An evaluation of temperament demands that we sum all the physical, mental and emotional qualities of an animal and then come up with words to describe him . Commonly used words are hardheaded, mean, spirited, kind, crazy, nervous, gentle and dumb.
The very nature of this process leads to tremendous variations. A horse that one person describes as spirited, might be called nervous or hard to control by someone else.
So it comes to pass that selecting an animal for disposition is a selective measurement determined on a personal level - at least until that horse is ready to market. Then you are faced with the general buyer's evaluation of disposition which may or may not be the same as yours. (With the present horse market becoming more naive it appears that docile is becoming a more sought-after temperament than spirited)
Whatever the sum of the horse's character, how does it apply to breeding better horses? How much of a horse's disposition is due to environment and how much is due to his breeding or genetics?
Because disposition is hard to measure quantitatively, getting an exact measurement for the heretability of this trait is difficult and not without controversy. The range of heretability estimates falls between 40% to 60% with 50% being the average. This puts disposition in the medium heritable range - the same as milk production. Basically, this means that we can influence about 50% of the disposition of the horses that we raise by selective breeding. Environment influences the other 50%.
We once conducted a landmark study to determine the influence a mare had on the character of her offspring. In this study all the offspring had the same sire and we defined the measurable character of disposition as position in the pecking order at feeding time - who ate first, second, third, and so on. We found there was a 70% correlation between the pecking order of the mares in relation to the pecking order of their yearling offspring. Those apples surely did not fall far from the tree.
The results of this kind of study make you wander about the wisdom of a breeding program in which a mare is placed in the brood mare band because she has such a bad temperament that no one want her as a riding horse - in spite of the fact that she has great conformation and a fashionable pedigree.
In our study, we did not look at the influence the sire had on an offspring's disposition. But if you assume disposition is 50% heritable, then 25% comes from the sire and 25% comes from the dam. We concluded that the reason we got the 70% correlation to the mother's peck order was due to the influence the mother had through the environmental conditioning of her foal.
These figures add creditability to what life-long breeders of horses have traditionally expounded. They believe that a mare contributes somewhere between 60% to 80% to the physical, mental and emotional abilities of her foals.
So, before you decide which mares will form the foundation for the horses of the next millennium, give weight to the idea that, in horses, the apple rarely falls far from the tree.
Copyright, 1999, Dr. Jim and Lynda McCall
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