YOU SAID:

i could eat a horse right now

INTO JAPANESE

私は今馬を食べることができました

BACK INTO ENGLISH

I was able to eat the horse now

INTO JAPANESE

もう馬が食べれました

BACK INTO ENGLISH

I've already eaten a horse

INTO JAPANESE

私はすでに馬を食べました

BACK INTO ENGLISH

I already ate a horse

INTO JAPANESE

私はすでに馬を食べました

BACK INTO ENGLISH

I already ate a horse