Question

how did the john byro react on seeing the white horse?

Answer 1

He was very happy as he found that his horse was strong than before

Answer 2

Mourad had stolen John Byro's beautiful white horse. John knew that who stole his horse but kept silent. 

When after three and a half months Mourad returned the horse to its actual owner, John declared that his horse was stronger than before. He was also better tempered than what he was three months ago.