Actually there is a very scientific answer to your question. The stud or the male is who determine the sex as he carries the X and Y chromosome. Research about the X and Y and who is faster and has more endurance and how the sex chromosomes play a roll in the way the sperm survives. You will find your answer . Also make sure you read about the age and the production of more Y and More X chromosome in a specific Stud dog. It is a very long answer to place here and i believe it is nice if you go to the scientific answer. Not a rule, but younger studs will have greater chance of producing more males than older studs. Also the mating and ovulation dates can help on the process as well. Y chromosomes swim faster, X chromosomes have more endurance!
Good luck in your "home work" .
XOXO
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