my mare has allergies and asthma and is losing her run after the second barrel and home. Not bleeding. Any suggestions for race day stuff and kr daily supplement 

My go to program for any horse I am running is by Cox Labs.  K C Plus (daily) and day of run Clear Passage (now known as Super Clear for Horses).

K C Plus: https://www.valleyvet.com/ct_detail.html?pgguid=aa0bbd1f-922a-42c3-bedd-837ad7c739e4

Clear Passage: https://www.valleyvet.com/ct_detail.html?pgguid=AAC1BCD0-73FE-4BEC-96B9-97FC05431C79&q=clear%20passage

Check with your vet to see if they have thoughts about a program.  Allergies and breathing issues suck .. human and horse.

I've got one with allergies and one that recovered from a bacterial and fungal

infection in the airway. Skip all the supplement / herbal junk and talk to your vet. My vet is big on nebulizing and makes me custom formulas for each horse . They basically get a combination of dex, dmso, gentimycin , and albuterol. Give the albuterol first , followed by the above mentioned combo. It's CHEAP. The nebulizer was 1300 ( flexineb) but it works wonderful and all the other cheaper ones just fell apart! I nebulize just equisilver couple times a week and then use the vet prescribed formulas few days before I run and an hour before I run. I have copies of my airway scopes on 3 horses to prove what a dramatic and effective method nebulizing is. When you nebulize it INSTANTLY gets where it needs to go and no side effects since it's not systemic . Spending money and waiting on a horse to eat something to build in the syatem is a waste of time

and money. 

To me it depends on the horses age, how old is she? As they get older and they have these issues your mare does I think they will get to slowing down as they age. Everybody is going to have a different answer for you on this subject, I would be asking my Vet about some ideals as what to do for her. 

Do you know the horse is not bleeding? Like actually got it scoped right after a run?

With allergies and asthma there is a good chance that it could be.. I'd start there. Make sure all allergens are eliminated from the horse.

Then I completely agree witht he poster above with the nebulizer. Invest in that and no herbal supplement crap. Those don't help humans athletes with asthma and allergies and dang sure aren't going to help you horse with asthma or allergies.

We use FlexNeb using albutrol and some other medications prescribed by the doctor.  

Yes we have scoped her after running.   All her allergens are gone as well. We use nebulizer as well 

During daily exercise are you having to use albuterol? 

Tried Ventipulmin instead? The company that makes ventipulmin also has a new inhaler for severe asthma you can ask your vet about.