We have a 5month old leonberger pup who is ridiculously healthy and growing well, but today she vomited (about half an hour after eating horse poo!) and has been asleep ever since and she vomited up all her lunch in the process (which was around 3pm) and she's not been awake to have her dinner.
Her nose is slightly hot, but not badly, should we wake her up and make her eat or just leave her till morning and see how she is?
could it just be a wee tummy bug?

It is probably just that "food" wasn't what she is use to or too rich or too much...just didn't agree with her. I'm sure she'll be fine.

I wouldn't wake her or feed her till morning. Let her upset tummy settle. But do provide water at all times.

I'd keep a close eye on her till she acts normal. Good luck. Let us know.

I phrased that badly..."keep an eye on her till she acts normal." No..... keep an eye on her and see if she acts normal in the morning. If not better to see the doc. You can also take her temp....rectal thermometer, k-y jelly, insert about 2 inches, leave for 2 minutes. Get someone she knows to hold her while you do that. Normal is 101.5 - 102.5. Farenheit.  A little outside of that is fine. 103.....get her to a vets.

Do let us know how she is doing. Best wishes.

Usually allow one vomit, worry a bit with two and off to the vets with three. As you know what caused the chuck up it is likely the pup will be fine now, perhaps a short bout of the trots.

However if the pup is not eating or still vomitting then I would take it to the vets as at 5 months they can go down quickly.

This may or may not be serious and may or may not be connected with the ingestion of horse dung. If the horse has just been wormed this could proved potentially dangeous to some dogs.