Male excessive bark at femal

I have a brother and sister who are now 16 months old. My female is spayed but my male is still a stud. Yesterday out of no where he started barking at her excessively and trying to nab at her neck and leg. He will not stop. He will bark for hours and hours. In the past when he had the "urge" he would go over to his puppy slipper. Now he has no interest in it. All I can think of (and now sure if this is correct) is that they went to the groomers for the first time last week (in the interum I have been grooming them) and had their anal glands secreted. Could this have something to do with it? Is the female letting out a scent and that is what is driving him to bark so? Sorry to sound so naive. Thanks for your input