Help! My dog's being pestered

I have a strong interest in Labradors as pets and working them on a shoot as a hobby.

I have had female Labs all my life. I have taken the last two (one chocolate, one black) shooting, both of whom were spayed and observed no odd behaviour from the male dogs we met shooting.

When I take my friend's female chocolate Lab (Finn) on a shoot all the male dogs behave as if she is in season, ie they follow her around with their noses up her backside, try to mount her and generally are a pain in the rear. This week, two of the males had a set-to over her when one tried to sniff her, which another didn’t approve of as he had his eye on her. It is beginning to be a problem rather than just a nuisance.

Finn is eight years old. She had a litter of pups when she was three and then was spayed. This happens every time I take her, October, November and January (I didn’t take her in December). Finn usually ignores the dogs who are pestering her, although sometimes she might snap at them. (I have taken Finn shooting since she was a pup, I think this behaviour started after she was spayed, as far as I remember, and gets worse as time goes on.)

The male dogs react similar to her daughter Kasey, who is also spayed and is five years old, but they are not so insistent with Kasey.

Could someone please explain what is happening? Will I ever be able to take Finn to enjoy her day out without being pestered?

Tracey Hammond, by email