My mare, Vegas recently broke out with hives all of a sudden after starting her on a biotin supplement and when we bought an orchard grass hay. She has been getting the same hay from the same ranch all winter and this orchard grass was also from the same place. She has eaten their grass hay previously and has never had any problems. After discontinuing the grass and the biotin supplement, the hives were almost gone within the 48 hours of appearing. I went down to the vet still and picked up a shot(some kind of steroid) and antihistamine granules. The hives were totally gone for about a week and a half. They have came back though. They are A LOT smaller and in less places but are still there so she is obviously still in contact with whatever she is allergic to. She is on the same hay she has been eating for months. She is only getting the purina minerals scoop as a supplement and getting her 9 lbs or so of hay each feeding. I looked around the property for any ants, weeds, etc. but there is no plants to eat nor bugs. Flies have not really came out for this year.
My horses have been on this new property for approximately 5 months and have not had any issues. But maybe there is something in the dirt that is bothering her??? I have no clue at this point as to what are causing these. Any ideas?
Last picture is probably 2 days after the other pictures.