Is it biologically possible to mate a cow and a stallion together aside from some differences in physical size.
The disparity in the number of chromosomes is large enough that I doubt you could produce a viable offspring. Cattle have 60 chromosomes, horses have 64. While it is true horses and donkeys have different numbers of chromosomes, Donkeys have 62, they can produce viable offspring, but the offspring cannot reproduce. Also the differences between them, digestive tract and foot structure, are such that an intermediate form is probably not practicle.
I don't know, but at least you could milk your transportation.
But, seriously, you can't mate them naturally, but of course you can with genetic manipulation in a petri dish. They even put jellyfish DNA slice bits in rabbits, to make them glow in the dark.
You could milk a horse if you really wanted to.
@GeorgeRocheleau That's how the Mongolians did it, and Arabs drink camel milk. I should have said, you can do dressage and have a drink of milk on breaks without leaving the room.
@GeorgeRocheleau when my mare foaled, the baby got an upper respiratory infection and couldn't nurse. My poor mare was so full of milk she could hardly walk, and the baby was dehydrated. I milked her several times a day, and taught the little guy to drink out of a bowl, in till he got well and could nurse again. Mommas was very grateful.
@GeorgeRocheleau horse milk tastes like sweet watermellon