I noticed my horse who has white feet, has a red line around one of his feet. It's on the outside of the hoof, about two thirds of the way down. Looks like blood under the surface of the hoof wall. He's not lame. He's one of my old retired guys. He's barefoot. Farrier recently trimmed him. What is this? 

 My horse that foundered ( now coming back into work after almost 6 months off) did that just prior to becoming lame and coffin bone rotation. Vet said that was the early signs of those laminae letting go from the hoof wall. 

Ooh, I hope it's not founder. He DID recently get trimmed. I've also been dealing with all of my horses' feet "crumbling." The bottom of the hoof wall is breaking off. They've all been barefoot for years and are living in great conditions. We attributed that to the dew on the grass in the morning and then drying out. Wet, dry, wet, dry. But there has been a lot of improvement since I've been giving them a lot of attention. Maybe this red line is related. He actually has them on both front feet. I didn't notice the other one until today. It's lighter and doesn't go all the way around....

Thanks for your help.