How Big is a Horse's Brain?

Two papers put the weight of an adult horse's brain at 598.63 g and 606.07 g, which is about 1.3 pounds in both cases. University of Padova researchers who weighed the brains of 131 horses describe a "large, convoluted brain, with a weight similar to that of other hoofed species of like mass."

Keeping a horse is similar on certain fronts to other pets, in that it needs care and love. This page covers what researchers have measured inside the horse's head: weight, comparisons with other animals, structure, and the signs a veterinarian looks for.

How Much Does a Horse's Brain Weigh?

The Padova paper, by Bruno Cozzi and colleagues, reports information on the horse brain "obtained by sampling 131 horses, including brain weight (as a whole and subdivided into its constituents)." It gives the result this way: "The mean weight of the fresh brains in our experimental series was 598.63 g (SEM ± 7.65), with a mean body weight of 514.12 kg (SEM ± 15.42)." SEM is the standard error of the mean. In pounds, 598.63 g is 1.32 lb.

A paper from Cornell University's College of Veterinary Medicine gives a second figure: "The adult horse brain weighs on average 606.07 g." It cites Cozzi et al., 2014, the Padova paper, at the end of that sentence. In pounds, 606.07 g is 1.34 lb.

The Padova abstract says "a modern neuroanatomy of this species does not exist and most of the data utilized in textbooks and reviews derive from single specimens or relatively old literature."

The paper also reports an encephalization quotient (EQ) of 0.78 and a cerebellar quotient (CQ) of 0.841, and it compares the horse with other species.

Horse, Chimpanzee, and Human Brain Weights

The Smithsonian's Human Origins Program lists an average weight for an adult chimpanzee brain and for a modern human brain. The chart sets those two figures beside the Padova mean for horses.

A Large, Folded Brain

The Cornell paper says the horse brain "has a highly convoluted and complex pattern of sulci and gyri," the folded surface of the brain. It adds: "The gyrification index for the horse is one of the highest in domesticated animals."

A third paper, an MRI study of the equine brain in the journal PLoS One, says: "The pattern of the equine gyri and sulci is by far more complex than in carnivores and in other ungulates." Ungulates are hoofed animals. The paper's discussion also says: "In general, the equine brain reflects the mammalian blueprint."

Parts of the Horse Brain

The MRI paper describes the brain of one horse, an "eight years old warm blood horse," scanned after death. The authors write: "In this study, we described one individual horse without taking intraspecies variation due to breed, age, sexual dimorphism, reproductive cycle and other confounding factors into account." They also say that "the description of brain morphology in the horse has been somewhat neglected."

Two details from that paper. On the lips: "Sensory information from the lips which are an important explorative organ is processed in the cortex surrounding the diagonal gyrus." On the cerebellum: "A characteristic feature of the equine cerebellum is the deviation of the vermis." The vermis is a part of the cerebellum.

The Cornell team built a brain atlas from nine unfixed equine cadaver brains imaged "within 4 h of euthanasia in a 3-tesla MRI." The atlas outlines these structures: olfactory bulbs, rostral commissure, caudate nuclei, globus pallidus, thalamus, hypothalamus, optic chiasm, pineal gland, corpus callosum, fornix, hippocampi, amygdala, mesencephalon, pons, medulla oblongata, and cerebellum. The atlas is free for researchers to use. The paper says the brains came from horses "previously euthanized for non-neurological purposes unrelated to this study."

Left and Right Sides of the Brain

In the Cornell scans, "All subjects had higher whole brain, GM and WM volumes on the right side, consistent with the well documented right forebrain dominance of horses." GM and WM stand for gray matter and white matter.

The authors cite earlier work for the behavior side: "a strong right forebrain dominance has been identified when horses process stressful, agonistic and social interactions." They also say the horses they scanned "did not undergo motor or sensory laterality evaluations and so correlation between behavior and imaging was not possible." On age, the paper reports: "Alterations in brain volume in relation to age were identified, though these variables were not found to be significantly correlated."

Learning and Behavior

Horses are prey, which is why they are born ready to move.

The Cornell paper says there is "growing interest in the horse for behavioral, neuroanatomic and neuroscientific research due to its large and complex brain, cognitive abilities and long lifespan." It also says the horse can perform "learning, discrimination, match-to-sample and memory tasks commonly used in neurological testing."

A systematic review in the journal Animal Cognition sorts studies of horse cognition into five categories: "Discrimination Learning; Learning Sets, Categorisation and Concept Formation; Spatial Cognition; Social Learning; and Memory."

Horses learn by associating gestures and cues with specific actions and behaviors.

Signs of Brain Trouble

The Merck Veterinary Manual, in a page by Thomas Schubert, DVM, DACVIM, DABVP, of the University of Florida College of Veterinary Medicine, says: "Signs of damage to the cerebrum and brain stem can include mental deterioration, constant pacing, seizures, depression, coma, or a head turn or circling in one direction." It adds: "A head tilt, bobbing, tremors, or other unusual head movements may indicate damage to the cerebellum."

Tell your veterinarian about any of these signs. The Merck page says that "Evaluation of the nervous system begins with an accurate history and general physical examination, followed by a neurologic examination." It lists common tests: "blood tests, urinalysis, analysis of the cerebrospinal fluid, x-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI), and evaluation of the electrical activity of the brain, peripheral nerves, and muscles."

Horse Brain FAQ

Do horses have two brains?

No. A horse has one brain with a left and a right hemisphere. The Cornell team divided the brain volume at the midline to compare the two sides.

Do horses have bigger brains than humans?

A horse brain weighs less. The Padova mean for horses is 598.63 g, and the Smithsonian lists 1,352 g for the average modern human brain.

Can a horse's brain be scanned?

Yes. The MRI paper says "Magnetic resonance imaging (MRI) is more and more used to evaluate intracranial diseases in horses with neurological signs." It also says that "it is unlikely that MR-images with a comparable resolution and contrast can be produced in a routine in-vivo examination" as the images in its study.

Sources

• Cozzi B, Povinelli M, Ballarin C, Granato A. The brain of the horse: weight and cephalization quotients. Brain, Behavior and Evolution (PubMed)
• Johnson PJ and others. Equine Stereotaxtic Population Average Brain Atlas With Neuroanatomic Correlation. Frontiers in Neuroanatomy
• Neuroanatomy of the equine brain as revealed by high-field (3Tesla) magnetic-resonance-imaging. PLoS One (archived copy of the PMC page)
• Smithsonian Human Origins Program, Brains
• Merck Veterinary Manual, The Neurologic Evaluation in Horses (archived copy)
• A systematic review on the effect of individual characteristics and management practices on equine cognition. Animal Cognition (PubMed)

Your world revolves around your horse and you know it. Know your horse, and you can have fun as its parent. You can get some apparels or gifts from the horse collection section to add sass and class to your horse parenting.

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