Emerency help needed!

I've had seven chickens die in 24 hours, all have had food, water, clean bedding. All from various stock but living together. None looked ill the day before fine in everyway possible.
Could there be a disease on my yard? I have Horses and sheep as well so could it spread?
I'm really worried
I need help quick to ensure this doesn't continue!
Thank you

I think this needs to be checked out by a vet as soon as possible. 

How sad fir you.
How old were they? What colour were their poos?

Have held off hoping for more information/feedback, but, hopefully not too late, are my thoughts.
Few diseases are common to horses, sheep and hens.
Few bacterial diseases are so uniform as to kill a large number at once - usually the incubation period is within a range. Questions as to colour of comb may be helpful.
Poisoning sounds very feasible, but most anticoagulants don't affect birds and take a long time to work.
You don't say how many birds you have or where they died. Description might help - again combs may show CO or cyanide poisoning.
Please tell us more/ what the vet said.
Best of luck.

Sorry everyone for not being in touch! Bizzare really what had happened!
The next morning i rung my vet and they said bring a dead chicken down so I did and they couldn't find anything wrong and said it was down to natural causes. I found this a bit strange seeing as so many had died!! Anyway they said they would send her off for further tests.
The next night (after moving my chooks into a stable) i left my horses in the field with the coop and at about 2:00am I heard my horses running and whinning, so i went up and there was nothing there!
I was getting a bit worried so i moved my foaling cameras in to the coop and when I looked the next morning turns out that there had been a fox climbing on to my field fence and then then over the chicken coop fence which is about 6ft tall. The fox was then sat at my coop scratting away at the door and side of it.
The next morning I had a phone call from my vet turns out that my poor chicken had died of a heart attack!
It's that time again and the foxes are about so just make sure everything is secure!
Safe to say i amended my coop before moving the girls back in and they are now all fine!!!

Thank you  At least i know what it is and can prevent it in future.
I hate this time of year when the foxes are about more.