If I'm not mistaken, I believe ACV has several uses in both human and animal kind. It is thought that when someone is sick or I'll, there is a pH imbalance that needs righted and ACV supposedly is able to help the body restor that acid versus base situation, though it has no impact on actually killing or overcoming any bacterial or viral infections. If I'm not mistaken, it has a healthy dose of vitamins, too.
I LOVE vinegar. It makes my mouth watering just thinking about it! My MIL uses ACV whenever she feels unwell or feels a cold coming on. She swears by it but I'm not convinced. Although, I add it to my water now and then knowing it has balancing properties to it.
As for me, I just add a splash of vinegar to my chickens water every time I refill it. I'm also told the vinegar causes the chickens to drink more than they normally do and this can help a lot in the warmer months.