Although this might sound like a myth, when we look at this statement from a scientific point of view it isn't too surprising. First of all, stairs aren't found in nature. They are man-made and are thus designed to suit human legs. The average slope of most staircases is around 35 degrees, which corresponds to a very steep hill. This, in combination with the human-sized steps, makes it incredibly difficult for a cow to walk down a staircase. However, as can been seen in the video below, some cows are able to tackle very short flights of stairs 🐮🐮🐮.
If you're interested and want to know more about cows, click here.
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Source
http://www.sciencefocus.com/qa/walking-down-stairs-impossible-some-animals
Picture taken from pixabay.com and edited by myself