Hopefully I'm being overly cautious - however my bitch (day 21 of season & 6 days post mating - 1 day post CHV vaccine) is quite lethargic and secreting a dark discharge.
Should I be worried ?

How dark?

One of my bitches bled until day 25 of her season ,quite dark blood which then tailed off to yellowy white and she had taken and went on to have 10 pups.lili

I wouldn't be happy with dark as in black at all but to still be bleeding 6 days after mating I would not think unusual or anything to worry about.

Can't comment on the vaccine as I never use it

Ali

I don't know that I'd be worried if it was just bleeding (as it would be if she was finishing her season without being bred) but I would NOT be happy with lethargic, is the discharge smelly at all? has it just restarted or has it been showing for a while? If it is new and she is off colour I would be inclined to check with the vet. can you take her temp? It may be nothing and it is obv impossible to judge vi the internet but  infections/pyo are something that needs rapid treatment.

let us know?

EDITED Just saw your other post that says she is fishy smelling, I would be very concerned and calling the vets emergency line personally. I'm not an experienced breeder of dogs but that does not sound ok to me at all. :-(
good luck

She has spent most of the evening engrossed in a game with her mother an starting around the garden - lethargic for her is short periods of laying down and not getting up each time we move - but sill very playful.
It more f the usual ' butcher shop' smell you get when they are in season ( sorry to be graphic ) and all of the other dogs are still cleaning her - she had started to go a lighter, thinner red but the past few days its quite a dark red/ brown .
Her tummy was felt and temp etc were taken yesterday when she had the CHV vaccination, so really the only change since then is that she is being cleaned a lot, still smells in season as still showing a lot of colour for the end of her season.

I have the vet booked already for Monday

If it's any comfort mine go a kind of browny red at the tail end of their seasons,mated or not.

Also the blood can smell slightly 'metallically'

Easy to say when it's not your own dog you are worrying about but nothing you say sounds too alarming

Ali

Ditto, metallic smell often more bloody after mating tailing off to old browner blood.

thanks all - it was browny and then stopped abruptly on Sunday last week