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Many pregnant animals display symptoms similar to those experienced by pregnant women. But not enough research has been done to determine whether pregnant animals suffer from actual morning sickness.

The nausea and vomiting that two-thirds of women experience during pregnancy could be the body's way of protecting the fetus from food-borne illnesses and chemicals that could be potentially harmful to the baby's developing organs, according to research by Cornell University evolutionary biologists published in a 2000 issue of the journal The Quarterly Review of Biology.

Veterinarians have noted that many pregnant animals similarly display a natural aversion to potentially dangerous foods.

"Dogs and cats are not thought to suffer from morning sickness nor is there any information detailing morning sickness in the reproductive literature of dogs and cats," Ann Hohenhaus, of the American College of Veterinary Internal Medicine at the Animal Medical Center of New York, told Life's Little Mysteries.

Hohenhaus went on to explain that when cats and dogs become pregnant, their ovaries produce high levels of the pregnancy hormone progesterone, which causes them to nest, produce milk and be protective of toys or objects as if they were protecting a litter of puppies.

Nesting refers to the strong urge a pregnant woman sometimes feels to clean, decorate and prepare her home for the baby. Scientists think pregnancy hormones are partly responsible for the seeming spring cleaning. Many animals, including prairie dogs and rabbits, will go into nesting mode before they deliver their young.