Do Horses See Color?

I had a student ask me a couple of weeks ago if horses see in color. I thought about it and said, “Well, as I understand it I don’t think they see all the colors we do, I think they see in shades of color…kinda like cats.” It was a reasonably lucky assumption on my part, but I wanted to know the specifics of if horses can see in color and what colors they do see.

It is a given that horses have a different field of vision than we do simply cause their eyes are built and located differently than ours. Because horses eyes are on the sides of their head (as opposed to the front like cats or like ours) the horse views a much larger field of vision.

In their book The Body Language of Hoses, published in 1980, Tom Ainslie and Bonnie Ledbetter state, “Many authorities have proposed that horses are nearsighted as well as color blind. Experimental findings support both contentions, but not persuasively.” (1)

As time progress our understanding and research progressed. As discussed in Desmond Morris’s book Horsewatching: Why does a horse whinny and everything else you ever wanted to know, published in 1988, he sates that “For many years horses were said to be color blind but we now know that this is not the case, although color vision is much weaker in them than it is in us. They are most responsive to yellows, then greens, then blues, and least of all reds, according to recent experiments.” (2)

William Micklem, in his book Complete Horse Riding Manual – published in 2003 – he says that “Research has shown that horses are dichromates, which means that they have limited color vision. They can distinguish between light and dark, between reds and blues, but not between greens and grays. This is why you will not find green or gray poles used in a grass showjumping arena.” (3)

Cherry Hill, in her book How to Think Like a Horse: The Essential Handbook for Understand Why Horses Do What They Do – published in 2006, she supports Micklem’s assertion that horses are dichromates. “The horse’s eye has two types of cone cells in the retina that are sensitive to color whereas a human has three types of cone cells. Whether horses can see colors as we do is still widely debated. Most researches agree that horses do have more than “shades of gray” discrimination but not the color range of humans. Exactly which colors horses see is sill unresolved.” (4)

“Equine vision expert Dr. Brian Timney, of the University of Western Ontario , explains that horses are like humans with color deficiencies. For example, humans with red-green color vision defects have only two hues (blue and yellow) rather than four. Such dichromates do not see intermediate hues, seeing instead white or gray or a faded form of the two colors.” (5)

“Horses have little difficulty in discriminating red or blue from gray. With respect to green and yellow, the results are mixed,” says Timney. His findings are similar to those from earlier studies but other researchers’ results differ. Exact answers have proven elusive in color vision research because of the difficulty in designing experiments with adequate controls (such as for brightness).” (5)

In the end, there is still debate about what colors horses see. It would be fair to say that there is a general agreement that horses can see colors, yet what colors those are remains to be conclusively confirmed.

End Notes:
(1) Ainslie, Tom & Bonnie Ledbetter. The Body Language of Horses: Revealing the Nature of Equine Needs, Wishes and Emotions and How Horses Communicate Them - For Owners, Breeders, Trainers, ... Other Horse Lovers Including Handicappers. William Morrow and Company, New York. 1980. Page 30.
(2) Morris, Desmond. Horsewatching: Why does a horse whinny and everything else you ever wanted to know. Crown Publishers, Inc., New York. 1988. Page 41.
(3) Micklem, William. Complete Horse Riding Manual. Dorling Kindersley Limited, New York. 2003. Page 46.
(4) Hill, Cherry. How to Think Like a Horse: The Essential Handbook for Understanding Why Horses Do What They Do. Storey Publishing, North Adams, MA. 2006. Page 24.
(5) Hanggi, M.S., Ph.D, Evelyn B. “How Horses See.” http://www.completerider.com/horsemanfeb2003.html. Feb 2003.

What is coggins or EIA?

I am the first person to admit that I don't know everything. So when I heard some staff at the barn talking about a coggins test, I thought to myself "what the heck is coggins?" I've never owned my own horse nor have I ever purchased one, so the massive amount of details, research and planning that goes into such a purchase are a little unfamiliar to me.

After a little snooping around I discovered coggins is actually the name of a test and a person. "The Coggins test (agar immunodiffusion) is a sensitive diagnostic test for equine infectious anemia developed by Dr. Leroy Coggins in the 1970s.” (1) The test actually looks for antibodies developed to fight the disease. (2)

This of course led to my next questions, what is equine infectious anemia? "Equine Infectious Anemia (EIA) is a viral disease for which there is no vaccine and no cure. Though most horses succumb rapidly to EIA a percentage of infected horses appear to recover. However they still harbor the virus and during times of stress may become ill again." (3) There is a vaccine that has been developed in China (2), but to the best of my research I was unable to find any information about its availability in the United States. Similar to HIV, EIA is lentivirus. Also similar is that EIA, like HIV, can be transmitted through blood, saliva, milk, and body secretions. Biting insects tends to be the most common means of transmission. (1) According to J. Warren Evans in his book Horses, 3rd Ed. "The disease affects less than 1 percent of the horse population.”(4)

There are three stages or sets of symptoms of EIA:
Acute: " The acute form is a sudden onset of the disease at full-force. Symptoms include high fever, anemia, weakness, swelling of the lower abdomen and legs, weak pulse, and irregular heartbeat. The horse may die suddenly."(1) "With acute infection the horse also has depression and no appetite. The acute horse may be difficult to diagnose because the symptoms are very general and he will not be positive on the EIA test for a month and a half. Approximately one third of infected horses will die of the acute form within a month."(3)

Subacute: "A slower, less severe progression of the disease. Symptoms include recurrent fever, weight loss, an enlarged spleen, anemia, and swelling of the lower chest, abdominal wall, penile sheath, scrotum, and legs."(1) “Subacute forms are less severe, so the horse survives.” (4)

Chronic: "Horse tires easily and is unsuitable for work. May have a recurrent fever and anemia, may relapse to the subacute or acute form even several years after the original attack." (1) "The chronically infected horse will having recurring acute bouts along with weight loss, ventral edema (swollen belly and legs) and anemia. These horses will be positive on a EIA test. These horses may linger for a year or more before they die." (3)

So what happens to a horse that has EIA? J. Warren Evans sums it up as follows:

“The temperature of an acutely infected animal rises to 105 to 108°F. The horse appears depressed, becomes weak, and loses appetite and weight. Fluid (edema) may collect under the skin, in the legs, chest and abdomen. Membranes lining the natural body openings may be congested and yellow in color. There is a marked drop in the number of red blood cells (anemia). The horse usually dies in a few days.” (4)

What did I learn from my little educational and inquisitive foray into the mystery that is "The Coggins Test"? Buying a horse is a HUGE decision and you should spend at least as much time researching and riding a potential new purchase as you would researching and test driving a car. The more time and research you invest the more likely you are to be satisfied with your equine purchase and well on the way to being a happy horse owner.

End Notes:

(1) : http://en.wikipedia.org/wiki/Equine_infectious_anemia

(2) Evans, J. Warren. Horses, 3rd Edition: A Guide to Selection, Care, and Enjoyment. Holt Paperbacks, New York, NY. 2001. Page 383.

(3): http://www.eqgroup.com/Library/coggins.htm

(4) Evans, J. Warren. Horses, 3rd Edition: A Guide to Selection, Care, and Enjoyment. Holt Paperbacks, New York, NY. 2001. Page 382.