The Dangers of Single Trait Breeding - How Iceland Did It Right

I’ve been recently reading Temple Grandin’s book Animals In Translation. I highly recommend the book as a whole, but there is one concept that she discusses in depth that has stuck with me.

In her chapter on Animal Feelings, she opens with a story about roosters that were accidentally bred to become rapist roosters as a result of single trait breeding. Grandin discusses extensively how genetic mutations happen regularly when animals reproduce due to copying errors in the DNA. Natural selection by an animal’s environment then promotes some traits and eliminates others over time. She goes on to say that, “when it comes to domestic animals, we’re the environment. We create the selection pressures.”

The problem is- we usually have less knowledge than we think we do when it comes to what selection pressures we may be enforcing over the animals we are breeding. We (often and unwittingly) breed for a trait that may very well be linked to another trait we do not find desirable.  In Grandin’s opinion, this is particularly risky when we start to breed for a single trait.

She writes: “It’s when you consciously and purposely breed animals to change one defined physical trait dramatically from what nature intended that you can definitely end up with some major emotional and behavior problems.  Moreover, when you’re trying to change a physical trait you very, very often end up changing an emotional and behavioral trait, too.”

Unfortunately, the horse world is rife with examples of single trait breeding. And Temple Grandin’s above statement rings true in many examples I can think of when it comes to horse breeds.  You have horses bred only for speed, color, specific conformational traits, or movement types. In all of those single traits-focused breeds, there are also emotional, behavioral, and even physical issues abounding.

I often say my liberty pony Cookie sports a trifecta of bad character genetics.  He is a mini - a breed bred primarily for size. He is an appoloosa - a breed bred mostly for color.  And he is a silver dapple which can be genetically linked to eye issues and other behavioral problems when homozygous. I knew from the beginning with Cookie that all these traits could be associated with a difficult temperament, but I never quite recognized the correlation between single trait breeding and these issues before reading Grandin’s book.

On the other hand, contemplation of this topic has led me to recognize that Icelandic horse breeders in all their glorious nerdiness dodged the single trait breeding bullet by a long shot.  Icelandic horses are often lauded for their great character and physical health/longevity. I now believe that this is less a breed coincidence and more a result of the fact that we breed for over 15 different conformational, gait, and temperament traits.

There are of course disadvantages to our multi-trait breeding system, and I think these should be recognized. Our breeding results are often unpredictable and inconsistent. Only a small percentage of horses consistently end up with the “whole package.” It takes more generations to work our way towards our breeding objectives- and lots of trial and error.

That said, I would take those challenges any day over the accidental development of chronic temperament and behavioral issues. I have so much gratitude for the earlier developers of our Icelandic breed assessments and the thought they put into considering the whole horse, as opposed a single trait.  And I have appreciation for our communities who continue dedication towards data collection and analysis as we consider all of the Icelandic horse traits moving forward.

I’ll leave you with one question that may be good for discussion. Would you consider breeding only for “good character” single trait breeding?