What is the number of horses present?

However, researchers from the National Institute of Environmental Health Services assert that,  

rather than five, there are seven horses in the picture  

The photo creates an optical illusion with what appear to be four white and brown horses and a foal huddled  

together and blending into the brown rock and snowy background.  

In this amazing optical illusion, how many horses can you see?  

If you can figure out how many horses there are, you have 20/20 vision.  

A team of NIEHS scientists claim that the image is composed of seven horses, some of which are only parts of horses,  

such as the head and hindquarters.