I'm not an expert with grades, but I can talk about crossbreeds!

With CBs, most people like to have a horse with a breed name, not something random,

 if you have a crossbreed you like working with, like one or two, breeding lots of them, selling them, showing them, etc! Like known crossbreeds, like the Cobbalstan, Cheyenne Trail Pony, and lots more!

You can also start a Crossbreed, and make it known by growing the numbers, and getting a second person that is interested in the new breed!

Just make sure you have alot  of ingots! Oh! And one more thing... make sure your new breed is not already made! If it is, you can always join!

To find these clubs, go to Town -> Clubs.

Hope I was helpful!

Grades are horses with an unclear lineage. Most players grade their horses if they want a specific gene on a specific breed; to do this, they have to crossbreed the breed that they are trying to grade with a horse that carries gene(s) of their desire. After that you continue breeding back to the breed of your choosing until you get a grade.

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For example: 

A player wants to breed a spotted Arabian, but they don't naturally carry those genes. They have to grade the Arabian instead.

Arabian x Knabstrupper = 50% Arabian (Crossbreed)

50% Arabian Crossbreed x Regular Arabian = 75% Arabian (the horse is still a crossbreed)

75% Arabian Crossbreed x Regular Arabian = 87% Arabian (crossbreed)

87% Arabian Crossbreed x Regular Arabian = 93.75% Arabian (crossbreed)

93.75% Arabian Crossbreed x Regular Arabian = Grade Arabian

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The only downside to grade horses is that they cannot be registered in the in-game registries, meaning that a grade would have to be registered in a club instead.

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Hopefully this helps! 

sorry if I was confusing

Thank you very much. You were both very helpful!

Of course!