How does Zhao know that the cow egg is his own?

Through Chou-heung's revelation, the character learned that Niu Dan was his own son.

It was a tortuous process for Zhao to learn that the cow egg was his own. At first, he doubted Niu Dan's biological identity because of his physical differences. In order to confirm his guess, Zhao decided to have a genetic test, and sent the blood samples of him, his wife Niu Dan and two other children to the Medical Research Institute for genetic analysis. The final result confirmed that Niu Dan was indeed the biological son of the Zhao couple.

However, in the TV series "Iron Pear", Chair Zhao learned the truth in different ways. In the plot of the forty-first episode, Chou-heung found Zhao and told him that Niu Dan was his own son. It turned out that Tie Lihua was pregnant before she escaped from the government and gave birth to Niu Dan. The fourth aunt was afraid that her son's embolus would be treated unfairly, and secretly exchanged her son's embolus for Tie Lihua's son Niu Dan. As an insider, Chou-heung finally revealed the truth to Zhao and committed suicide.

Therefore, Zhao learned that Niu Dan was his own, not only through scientific detection, but also through the plot setting revealed by the characters in the play. These two ways together constitute the complete process of Zhao's learning truth.