Me and my sister got encircled once by about ten cows while we wanted to visit our pony which was on the same absurdly big pasture. As they closed in, our little Shetland pony raced in to our rescue and showed them who's boss in seconds. That was surprising in multiple ways. Especially as I didn't expect ponies to be that protective to their scratch givers.
I hope your dog was able to overcome the trauma with time and therapy 😅