Mare that acts like stallion

I have a 5 year old bred, paint mare. She is due April 28, 2003. She is out in the pasture with coming 2 year old fillies. I know she's bred as she is huge. My question is why does she act like a stallion?I have a 5 year old bred, paint mare. She is due April 28, 2003. She is out in the pasture with coming 2 year old fillies. I know she's bred as she is huge. My question is why does she act like a stallion?

Story originally posted by: Michael Lowder, DVM, MS

Hi Dr. Lowder,

I have a 5 year old bred, paint mare. She is due April 28, 2003. She is out in the pasture with coming 2 year old fillies. I know she’s bred as she is huge. My question is why does she act like a stallion?

When the fillies come in heat she rides them. Also chases them around and snorts. I have never seen any horse ride another horse before. Is there a blood test I can have done to see why?

Thank you.
Rhea Eblen

Rhea,

I would not be so sure that she is bred. You need to have the vet palpate her ovaries to make sure she does not have a tumor (Granulosa cell also called a theca cell tumor) which would account for the behavior you are talking about.

Thanks,
Dr. Lowder