I have a bitch that I am going to mate very soon, The stud owner will only let me use her boy if my bitch is on a course of Synulox for 7 days prior to mating, My question is my vet gave me 300mg daily for my bitch {Terrier} and the stud dog owner told me that 200/250mg would be enough, Has anyone else used this before and do they agree with the dosage.

Synulox is given by weight and if your vet has given you 300mg daily that I would stick to that

I strongly disagree with giving any antibiotics unless there is a reason to do so - mating is not a reason - an infection that is unlikely to clear up on its own or to cause other problems is.  You could kill off some natural flora and cause rather than prevent problems.

One of the reasons we have MRSA and other anti-biotic resistant diseases is because of over prescribing and bodies (human and canine) becoming resistant to the anti-biotics.

By all means have your bitch swabbed and if there is anything other than the normal vag*inal flora then consider whether she should be mated and what is actually wrong with her.  If she does have a problem then Synulox may not be the appropriate antibiotic anyway.

I would think, if the stud-dog has been used at all that your bitch is more likely to pick up an infection from him than vice versa - neither are very common.