My vet says it takes about 6 months for an already sexually mature dog to lose its testoserone levals. I know I have always had all my critters done the 2nd they turn 6 months old. The only ever issue any of mine had ever had was stress diarreah for a few hrs after coming home. Mind yoiu my one male still insists on marking and trying to hump when my aunts f/m westie is around....