My bitch is not due in season until end February, around 2 weeks ago she started loosing a clear, odourless discharge.

I have two males.
One very experienced stud (boy 1)
One only mated once, but only mated for 3 days from ovulation as per progesterone testing so waited for exact time (boy 2)

They was both interested in her going to the loo but I was checking her throughout and discharge just clear no blood or colour whatsoever.

On the 12th I saw boy 2 very interested trying to mount her she was not flagging or standing her and boy 1 didn't batter an eyelid, took her to the vet he swabbed her says discharge no concern wrong dates from last heat for pyometra gave me 7 day antibiotics just in case (she has been fine through out, eating, playing etc)

That evening she tied with boy 2 I seperated her for two days both boys not bothered no crying/whining/refusing to eat as they usually do when she is in heat and kept seperate it is usually hellish.

I did a lot of reading online and imagined maybe she smelt different from the discharge and was a uti that was why they tied, put them back together when supervised neither boy show any interest what so ever two days later she tied again with boy 2 no flirting, flagging or anything was happening she didn't cry or seem upset when they where tied (they have been seperated all times when unsupervised so I know nothing happen when I not around)

Now she has run the course of antibiotics she has no discharge anymore, I was checking several times a day and each time was just clear non smellty discharge, no swelling no flagging etc no interest from boys but they wasn't acting like she was in heat at all.

Do you think it was a silent season but if so why was boy 1 not interested what so ever usually he is going crazy shivering and shaking why she is in heat,  and boy 2 randomly tied twice is itt because of the discharge why did they tie does anyone have any experience of situation like this.

Just to add dogs are, KC registered, patella tested, correct bites and of excellent lineage with lower than average coi, I did hope to have puppies from them at some point

Also.. I did try to mate her before and she had a phantom pregnancy, not sure if it is relevant?

Who knows why - only the dogs know, sometimes.  But a bitch will only accept a male when in heat.  So you can be sure she was in heat, whatever colour her discharge.  I hope you wanted this mating because there's the usual chance of puppies...

I have been caught out by this EXPECT pups in 9 weeks.
I was shocked as I hadn't even seen a mating taking place although not planned I had intended to mate them later when in season.

Did your boys usually show interest in her other heats, this is what confuses me as usually it's very obvious she is in heat to everyone in the household?

Yes he did but this was a first-time mating and I hadn't thought he was ready yet, clearly he was.

I have heard of rare instances of bitches allowing a mating to take place when not in season.  One that springs to mind was a spayed bitch, with a newly rescued entire boy who had never been taught any manners, and he pestered her until he managed to mate, I'm not sure if a tie happened but the owner was mortified as they thought it couldn't possibly happen with a spayed bitch.

I had a neutered male dog tie with a bitch who was not in season. She was however on the verge of pyometra and ended up being spayed ASAP.

Usually when this happens, there is some other underlying cause. Like the pyo or like ovarian stump remnants in spayed bitches....

Thanks for the comments, discharge definitely ended and no sign on infection or being poorly, will keep you updated if any pups