Breeding Horses/herd stallion refusing to breed "outside" mares
We are a very small ranch in South Texas and we consider ourselves pretty much experienced at standing stallions to the public ( had 3 stallions and 21 broods for years). The problem at hand is that I have a 11 yr old APHA homozygous stallion that we have been standing at stud to the public for 8 years. He runs with his own "herd" of mares year round that he pasture breeds (with 100% conception) and we have hand bred him to over 30 outside mares over the years. Last year we did not breed him "out" and he only stayed with his herd of three mares and colts. This year I have bought several new mares and have 2 "outside" mares here at the house to breed to him right now. I have not introduced my new mares to his herd as of yet since we always wait to introduce herd mares when they are in heat but with is aggressiveness I'm keeping them here at the house since I'm afraid for their safety. We have previously found that he has NEVER had an issue with hand breeding outside mares as long as we bring him to his breeding shed to service them there~~ never taking them to "his" pasture. This year though, even though all of the mares were in heat and pending ovulation (per ultrasound), he refuses to breed any of them, and is "snaking" them with low head and flattened ears as well as baring teeth at them. He has Absolutely NO interest in breeding them, only in attacking them. The mares are terrified of him as it only takes flattened ears from him to get them on a "flight" pattern. This is a stallion that has always been very easy to handle and a gentle breeder to any mare with No biting, or aggression. If a mare kicks at him or lays back ears, he was through with her until she was ready. He can tell by a flipped up lip whether or not she is ready to breed and he wont breed her if her hormones tell him that she isn't. So with that little bit of background whats your thoughts? This new personality change is not to normal for him. Should we pull him from is "harem" and keep him stalled at the house until this attitude changes or is there other things at hand that we may be missing? Currently he is stalled next to two of the mares where they can touch noses through the bars. He totally ignores them, only pacing to get back to his herd. When he is teased with them, he will show a little bit of perked ears, and snorting, but nothing like is usual voicefulness and licking them, then when brought around to their rear for his inspection, he immediately goes into attack mode. We are almost at the point of sending the mares back to owners and refunding monies.
Your stallion is displaying typical herd behavior. If they do not "belong" to him, then he wants them gone. Another issue you could be having is that he is so used to pasture breeding, that he does not want to hand breed.
Take him away from the herd, if you have a gelding then pasture them together for companionship. If not stall him and introduce him to each mare individually. You can also stall him next to the mare that you want to breed him to. A few tricks you can also use is put Vicks under his nose or take a rag an rub it on one of the mares he likes and then all over the outside mare. This way the sent he likes is all over the outside mare. In the future, you might have to choose between hand breeding or pasture breeding if he does not improve his behaviors.