YOU SAID:

I took my horse for a walk in the countryside, but I turned around and my horse was gone.

INTO JAPANESE

馬を連れて田舎を散歩したのですが、振り向くと馬がいなくなってしまいました。

BACK INTO ENGLISH

I took my horse for a walk in the countryside, but when I turned around, the horse was gone.

INTO JAPANESE

馬を連れて田舎を散歩したのですが、振り向くと馬がいなくなっていました。

BACK INTO ENGLISH

I took my horse for a walk in the countryside, but when I turned around, the horse was gone.