Engyu - Engyu

...This is called hormonal castration, and because it is easier than surgical methods, it was once used for chickens, which needed to be processed in large numbers, but its use is now prohibited due to the risk that the administered hormones may remain in the meat. In the past, castrated male horses were called geldings, and male cattle were called steers. [Masada Yoichi]
[Parasitic castration]
Parasitism causes changes in the host's reproductive glands and secondary sexual characteristics, but the degree of change varies, and in many cases the term castration in the true sense of the word is rather inappropriate.

*Some of the terminology explanations that mention "unushi" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…これをホルモン去勢といい，外科的方法よりも簡便であるので，大羽数の処理が必要なニワトリで一時は用いられたが，投与ホルモンが食肉中に残る危険性があるため現在ではその使用は禁止されている。なお，古くは去勢された雄ウマを騸（せん），雄ウシを閹（えん）牛と呼んだ。【正田 陽一】
［寄生去勢parasitic castration］
　寄生によって宿主の生殖腺や二次性徴に変化を生じることであるが，その変化の程度はいろいろで，真の意味での去勢の語がむしろ不適当な場合も多い。…

※「閹牛」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報