Final answer:
The world's largest ruminant by weight with females called 'cows' is the giraffe. Ruminants like giraffes have specialized stomachs and are ungulates, which means they have hooves to support their body weight, unlike elephants, hippos, or blue whales.
Step-by-step explanation:
The world's largest ruminant by weight, whose females are called 'cows,' is the giraffe. Contrary to the other options listed—elephant, hippopotamus, and blue whale—the giraffe is actually a ruminant, which means it chews cud regurgitated from its rumen.
Elephants, hippos, and blue whales do not chew cud; elephants and hippos are not even ruminants, and while blue whales are mammals, they are aquatic and have a completely different feeding mechanism involving baleen plates for filtering food from the water.
Ruminants are characterized by their specialized stomachs, which have multiple chambers to aid digestion. Giraffes, being ungulates, also possess hooves that sustain their whole body weight. This is a trait they share with other ungulates like deer, sheep, goats, and elephants. However, only the giraffe meets the criteria of the largest ruminant by weight with females referred to as cows.