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The Brain Size of a Cow

i David De Lossy/Photodisc/Getty Images

A human's brain consists of more than 2 percent of his body weight. A mouse's brain is more than 3 percent of his total weight. The brain of a cow, in contrast, equals only 0.1 percent of her body weight. It is roughly the size of a baseball.

Average and Estimated Brain Size

The average cow's brain weighs 450 to 500 kilograms -- just under 1 pound. A cow's brain size increases from birth over the course of her lifetime; various breeds exhibit slight differences in brain size. Steer brains weigh in between 92 to 94 grams per 100 kilograms of body weight, while bull brains range from 85 to 97 grams per 100 kilograms of body weight. Cows weigh less than bulls and have brains weighing less than 85 grams per 100 kilograms of body weight.