Twenty-five of the top US burger chains were graded on their antibiotic policies in a collaborative report released Wednesday. Only two chains received As, Shake Shack and BurgerFi; the other 23 got a D minus or F.
"It's really exciting to hone in on beef because we know that Americans love burgers. It's one of the most favorite foods in our country, and taking a closer look at what is and isn't happening when it comes to responsible antibiotic use in that sector seemed particularly important," said Lena Brook, lead researcher of the report and interim director of the food and agriculture program at the nonprofit Natural Resources Defense Council, one of the organizations involved in the research.
今回はhorn in /hˈɔɚn iːn/を取り上げます。『ジーニアス英和辞典』（第四版、大修館書店）には「でしゃばる、首を突っ込む、干渉する」とありました。OEDには"Intrude or interfere."と定義されています。記事からも分かるようにonで何に干渉するのかを表すようです。
「話に割り込む」もこの表現を使うことができます。辞書の例文にはHe horned in on our conversation and monopolized it.とありました。
cf. butt in, poke one's nose