The Brain of the Horse: Weight and Cephalization Quotients

Abstract

The horse is a common domestic animal whose anatomy has been studied since the XVI century. However, 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. Here, we report information on the brain of Equus caballus obtained by sampling 131 horses, including brain weight (as a whole and subdivided into its constituents), encephalization quotient (EQ), and cerebellar quotient (CQ), and comparisons with what is known about other relevant species. 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). The EQ was 0.78 and the CQ was 0.841. The data we obtained indicate that the horse possesses a large, convoluted brain, with a weight similar to that of other hoofed species of like mass. However, the shape of the brain, the noteworthy folding of the neocortex, and the peculiar longitudinal distribution of the gyri suggest an evolutionary specificity at least partially separate from that of the Cetartiodactyla (even-toed mammals and cetaceans) with whom Perissodactyla (odd-toed mammals) are often grouped.

Mapping of the Early Intrauterine Morphogenesis in the Alpaca (Vicugna pacos): External Features and Development of the Cephalic Vesicle in Comparison with the Progressive Carnegie Scale

“…The alpaca is a species with considerably long gestation (340 days) and possesses a gyrencephalic brain (presenting sulci and gyri). These morphological and gestational characteristics are closer to other Cetartiodactyla, such as pig ( Sus scrofa ), bovine ( Bost taurus ), sheep ( Ovis aries ), giraffe ( Giraffa camelopardalis ; Ballarin et al, ; Graïc et al, ); Perissodactyla, as the horse (Cozzi et al, ); and apes. The specimens that we used in our experimental set were accompanied by notes referring to the age (in days) of the embryos and fetuses.…”

“…This stratification reflects the process of differentiation and migration of the germinal neuroepithelium cells that will eventually form the cortical columns of the neocortex (Gilbert, ), here organized in five layers as typical of large herbivores (Cozzi et al, ; van Kann et al, ). However, here we note that adult Cetartiodactyla and Perissodactyla, contrarily to rodents and primates, are generally considered to be endowed with a five‐layered cortex, for further discussion see (Cozzi et al, , ).…”

The Brain of the Giraffe (Giraffa Camelopardalis): Surface Configuration, Encephalization Quotient, and Analysis of the Existing Literature

“…The giraffe seems to have not only the biggest brain among terrestrial Cetartiodactyla in absolute mass, together with the hippopotamus, but also the largest EQ (Table ). It is notably lower than that of the odd‐hoofed horse, with 0.78 (Cozzi et al, ).…”

“…First of all we emphasize that our values originate from a direct calculation of brain and body weight derived from captive, but well housed, fed and groomed, mature specimens. Second, intraspecific variation may sometimes yield huge differences: In a recent study of our group (Cozzi et al, ), 7 out of 131 horses showed an EQ in the cat or primate range. An EQ of 0.76 for the giraffe is also more consistent with the Ruminantia clad (0.86, Boddy et al ; Ballarin et al ).…”

“…On the whole, the brain of the giraffe is comparable to that of other terrestrial Cetartiodactyla, and shows a high degree of gyrification, without the rotations and compressions found in more distant Cetartiodactyla such as the bottlenose dolphin (Cozzi et al, ). High folding adaptation of the brain ontology suggests surface enhancement in a relatively smaller space, compared to species with a similar brain weight (Pillay and Manger, ).…”