The question sounds extraordinary, even ridiculous. However, a study concluded that free-living stallions in the USA preferred mares of a certain coat colour. For example, one stallion preferred buckskin mares while another chose bay mares. And a third favoured very pale-coloured mares. I tried to find this study on Google Scholar but failed. I am therefore reliant upon the reporting of Dr. Desmond Morris.
He writes that the experts do not know for certain why some stallions are in effect racist. I am using strong language but that is pretty well what it comes down to in terms of human concepts. Although it is fair to say that the term “racist” is inapplicable to horses if I’m being totally honest. I am anthropomorphising horses but it is interesting because I don’t think many people realise that horses have preferences or prejudices for and against female horses of different colour. Lionesses like lions with dark manes and unsterilised female domestic cats are selective, perhaps choosing males that she believes will produce healthier offspring.
I know people are unaware that horses can have a color prejudice because when I performed a Google search, Google did not make any suggestions as it normally does on the issue of horses and racism! Perhaps I shouldn’t be surprised.
It is speculated that the reason why some stallions have these prejudices is because they are fixated on their mother’s coat type and colour. Perhaps they have become so attached to their mother when they were being nursed that they carry this fixation into adulthood to where it becomes inconvenient to humans who want to try and mate a highly treasured stallion with a great track record with a mare who is the wrong colour.
It’s a known fact that sometimes stallions simply don’t want to cooperate and mate with a female offered to them. The people managing the stud male and the chosen female, cover the female with a large horse-blanket to hide her coat colour. In fact, the blanket is the colour of the stallion’s mother.
Dr. Morris provides us with an example. The stud male in this instance was the offspring of a Derby winner who point blank refused to mount any grey mare. His name was Little Cloud. He would only perform with females if they were draped in a rug to conceal their ‘offending whiteness’ in the words of Dr. Morris.
Stud males are not given free choice or allowed to meet any females other than those that the organisers provide to him. This is because he will be very valuable being a past winner and the owner and stud manager will be concerned about him being injured by a kick to the chest by the female. It is sad that his life is so constrained and limited.
The female is provided with a ‘tease-stallion’ to get worked up and in the mood for sex. It is hoped, then, that she will stand quietly while the stud male gets on with his business. He is led in and encouraged to mount her straightaway without any courtship.
If there is a possibility that the female may strike out, they cover her rear feet with a protective material to soften any blow that she might deliver or they hobble her so that she is incapable of resisting the advances of the highly valuable stud.
Below are some more articles on horse behavior.