So a little background. My mare is a seasoned show horse, trailers comfortably, has no issues traveling to shows, trail rides and has shown off the trailer quietly for years! Last year I started her hunting- I was most worried about her going through mud and water, well she got over that easily! She went out last season about 6 times, our season here in the south is short with barely any cub hunting, so 6 times was solid. We went between 2nd and 3rd field so she could have some more action and then come back down to a very slow pace in an effort to not overface her warmblood brain. After a few hunts she started quivering as soon as she saw the trailer arrive in the am. She would do it on and off during the hunt and it got worse the more I hunted. She does get 1 cc of ace early am ( probably 2+ hours before we hunt as we have to drive at least an hour for any fixture). The first time she really quivered a lot and I was concerned she was tying up. Had the vet out the next day to pull blood and she had no signs of any veterinary issues, so that was a relief. Anyway, at several of the hunts, she just couldnāt settle enough afterward and I would have to skip the breakfast. We have most of our breakfasts in the field since the majority of the membership travels from many different directions. I have tried leaving her on the trailer- which has fans, a nice big stall bedded up, hay net, water, etc. She fussed, and pawed and acted like a nut! I have also tied her to the trailer ( not my favorite solution). She was a bit better tied to the trailer but still not quiet enough I felt safe walking away. She cant seem to relax in either place. She is lovely during the hunt- in fact she is all business- ratable, forward but controllable, has no issues with hounds around her or in the the brush, other horses donāt bother her. Really, she is lovely and fun. Its really just back at the trailer that she cant seem to realize the day is over and she can chill. She can even be a little wide eyed when we get back home for a bit depending on the day. I donāt want to push her if she hates this new endeavor! As a side note, I have owned her many years and know her very well- but this behavior has me a little stumped. Any help would be appreciated!
If sheās happy during the hunt, she enjoys it.
Could it be a reaction to the Ace?
I would plan on skipping the after-hunt social scene and call it a day. You had good hunts, right?
Next idea, assuming you travel alone. Find someone to pair up with to share the rides to the hunt and back.
Next, could she be in pain at some level after the hunts? Unless by showing you mean that you event, fox hunting could be very physically demanding for her compared her typical trip to a show.
I have wondered that- i would think it would be pretty much out of her system close to 5 hours later- but I am planning on skipping it moving forward. If I have to give it to ship home, I can also do that if necessary. In general, once we are on our way headed home, she is happy. She just really does not want to stick for the after party 
She has competed at a pretty high level of Hunters - I donāt think it pain. She gets very thorough veterinary care and we have been through some lameness issues in the past - the hunting is really easy on her compared to showing at the AA level ! I wish she had a horsey hunt buddy, unfortunately no one from my farm hunts their horses and i am not close to anyone that does, so the buddy system isnāt an option for us. For now, I go to the breakfast for just a few minutes and head home, hoping as season unfolds she will start to get a little better about it, but for now, yes, I leave early.
New job, new stimulus, treat her like a baby horse. Minimize the standing around donāt leave her to go have breakfast.
Does she get freaked going to shows in the trailer? Do you Ace her for traveling to shows too?
I think you need more miles. Trailer out in the morning and trail ride quietly. Alone or with a buddy. Mix it up
Is this her only off property non arena work? Then mix it up with quiet trail rides so she stops anticipating.
Iād also cut out the tranq. Itās not helping her learn to.self regulate.
I agree with ehat @Scribbler said. Also you can try a supplement with valerian (if allowed but I donāt think itās forbidden). I use one with my appendix, heās not a travelling fan so at the beginning of trails season I give him this supplement and it seems to help him a lot
Showing is very familiar and probably rather boring for her. Hunting is new, huge fun, in stimulating company and she hasnāt yet done enough to learn to pace herself and rest. Six times out is very few: think total greenie doing first six shows. The probable solution is more hunting. Move her up in the field to go faster and get her tired, push her on rather than holding her back, and she will learn that hunting can often be a lot of work as well as fun. With more experience, she will learn the value of switching off during a hold.
When you are done, go home, donāt hang around for your social time. If she is still quivering at home, hand walk her until she calms down in a familiar place. As she learns more you will eventually be able to leave her while you join the social activities. You know her well and will be able to judge when she is at that point.
Do trail rides with her, taking her out to new places and pretending to yourself that you are hunting so push on a bit, avoid thinking āshow horse, avoid mudā. She will likely improve as she stops anticipating every journey means that her new favourite-thing-ever is about to happen.
Some horses, in my experience, will shiver with anticipation even when tried and tested hunters. Donāt worry. What is more important is that they switch off back home and eat up their dinner. Some horses will be so full of their day out with hounds that they box walk, sweat and wonāt eat. That is when being able to turn them out is helpful as it allows the adrenaline to subside and movement helps prevent any stiffness.
Congratulations, looks like you might have a keen field foxhunter on your hands.
Thanks so much- good to know others have dealt with the quivering and excitement. i can skip the breakfasts ( for now anyway ā¦ I mean that is a lot of the fun! ) and just head home after. She does settle by dinner time and eats fine. I agree that 6 hunts is really not much and really about the time they start to get to really figure out the game and that was my suspicion. I have had a few other hunt horses Iāve made up, but they were TBās and the warmblood brain is NOT the same for sure- and while it has been an asset with showing, it has been a challenge for parts of hunting. Thanks for the encouragement and support!
She just loves hunting a little too much! 40 years of caring for hunt horses here. The trembling and shaking is anticipation. Some start when getting groomed in the morning, some on the trailer. Often they are āhighā after a hunt for a while. In my experience, this is not a reaction to ace. If the prehunt jitters are not causing a problem, I wouldnāt worry about it. A longer dayās hunting is the best help for the post hunt issues! But out of your hands. You may have to forego the breakfast for a bit. I would hand walk her a bit, catch some breakfast while holding her if you can. People are generally very understanding and willing to help. When you load her up leave right away. Donāt let the trailer become a place where she feels isolated and unhappy after having had SO MUCH FUN with her friends. It sounds like you have done a great job introducing her to hunting! Happy New Year!
Quivering after exercise can be a sign of selenium deficiency. Or magnesium deficiency. Anytime you engage in new activities with your horse, especially one as stimulating as hunting, the stress depletes magnesium and other nutrients. Add Mag Restore or another magnesium supplement to her diet and see if it helps. And maybe a Selenium/Vit E supplement also. If she already gets magnesium she may need more during hunt season than the rest of the year.
My mare always would shiver/quiver when I loaded her to hunt. She loved hunting. I did make an effort to take her other places so she didnāt think every trailer ride was a hunt and I also would give her some alfalfa in her hay bag after so she had a nice lunch while I had mine.
My TB gelding used to get quite worked up about hunting. Until we went out for 4+ hours. He learned how to rest that day 
and it stuck.
Your horse will likely settle down once she learns her new job. Iām with those who say celebrate that you have a nice hunt horse and leave early until sheās ready for you to stay longer.
Everyone else is probably right but just in caseā¦ does she happen to be chestnut? My chestnut tb gelding started quivering/shaking after a trip to school in a large dressage arena. (He definitely wasnāt amped up over circles 
) we worried about tying up, called the vet - horse had no other symptoms of tying up. he asked if I had used liniment. I had! The vet said heās seen chestnut horses shiver uncontrollably after liniment. So I put him back in the wash stall used lots of warm warm water to rinse it off and walked him in the sun and it went away. It was so bizarre. The vetās theory is the tingly sensation mimics cold and so the horse shivers uncontrollably.
Crazy huh?
Iām in the camp of wondering if she just really likes hunting! My friend that competes endurance, his horse knows when they have a race coming up because of the training/rest schedule shift and he gets more to eat leading up to the race.
I could walk into the barn and based off his horses demeanor, I could tell there was a race coming up. That horse would RUN into the trailer because he knew it was race time!
Always good to make sure there is nothing off health wise, but 100% but when I read through your posts, my first thought was that it sounds like she might have found her thing!
Is it fun/anticipation quivering and restlessness or fear/anxiety trembling?
Is there someone with a dead quiet, totally relaxed after the hunt no matter whatās happening horse that you can park near? Tying your horse within sight of a relaxed neighbor might help. What about walking her out and letting her graze for 10-15 minutes after untacking to give her time to relax?
Just in case itās tummy trouble, I would try ulcergard and sucralfate, and alfalfa in the trailer. My show horse turned hunt horse never needed tummy meds while showing but definitely gets amped and ulcery on hunt mornings. So now she lives on a low dose of ulcergard, and sucralfate on hunt mornings, and it helps a lot.
I think she loves her new job and her new friends; running in company has got to be the best thing ever for a horse. But loading her up then not going anywhere, or even tied after may be giving her the anticipation of not knowing whatās coming next, on top of the chemical let down of it all. I would load up and go right away to reinforce the idea that it is all done, give her grazing at home, as suggested. I also think any chance to wear her out on a harder or longer run will do her alot of good also. Sheās a keeper!
I donāt think sheās saying she loves her job. I think it is stressing her out. I agree the tummy issue stuff that 2bayboys posted. According to the OP she has been trail riding and showing and hasnāt had these issues. They donāt seem to be anticipation, but reaction. Hunting is so noisy and has to seem chaotic to a horse that hasnāt hunted much, I think sheās just stressed after the hunt. BUT I bet she also gets better as she gets more used to it.
