The Border Collie check, reduced to spacing
A young Border Collie is male when a rounded genital opening sits on his belly a clear distance from his anus, and female when a slit sits almost directly under her tail. Nothing in that sharp, watchful Collie face or in the black-and-white markings separates the sexes at this age. Even size is unreliable, because littermates grow at different rates and a bold female can easily outweigh a quieter male. Spacing on the underside is the one feature that stays consistent from the first weeks of life onward, so that is where your attention belongs.
Settling a puppy who would rather be working
A young Border Collie rarely holds still out of politeness, so timing matters more than technique with this breed. Wait until after a short play session and a meal, when the puppy's eyelids are drooping, then sit on the floor and let the little dog climb into your lap voluntarily. Cradle the chest, tip the puppy gently sideways rather than flat onto the back, and keep one hand ready for the sudden twist this athletic breed produces. A helper offering a fingertip of soft food to lick can buy you the ten quiet seconds this check actually requires.
What marks out a male Border Collie
On a male Border Collie, part the short belly hair between the hind legs and look forward along the underside for a small, slightly hooded bump with a central opening. That belly position, roughly midway between ribcage and tail, is unmistakably male. Nearer his anus, tucked between his back legs, a very young male may show only a faint seam rather than obvious testicles, because descent happens gradually. His lean, tucked-up Collie belly actually helps here: with so little puppy fat, the prepuce stands out clearly once the coat is brushed flat with your palm.
What marks out a female Border Collie
On a female Border Collie, run your eye along the belly and you will find only a small flat scar from the umbilical cord, with no raised opening anywhere along it. Her genital opening hides under her tail instead, a narrow vertical slit positioned immediately below her anus, so close that the two openings almost stack. In a black-coated puppy the contrast can be poor, so use bright light and part the hair with your fingers rather than relying on a quick glance. If everything you can find sits in that tight under-tail cluster, you are looking at a female.
Traps specific to this clever breed
Do not let behaviour talk you into a verdict, because a young Border Collie bitch may hump toys, herd siblings roughly, and cock her leg against a chair, while a young male may squat to urinate for months. Coat length tricks people too, since the longer rough coat can bury a male's belly opening until the hair is deliberately parted. Checking a half-asleep puppy in dim evening light is another common route to a wrong answer. Repeat the look in daylight, fully awake yourself, before you commit a name and sex to any record or collar tag.
Confirming the answer before it follows the dog
Have the veterinarian confirm your Border Collie's sex during the first puppy examination if the underside check leaves you unsure, and ask promptly for an appointment if you see swelling, discharge, or difficulty passing urine at any point. A confident home reading is normally enough, but a professional confirmation removes doubt before training plans and health records build on the answer. Once confirmed, storing that sex on the KinsLe Pet Pass means this Collie's verified identity card shows the correct details whenever you need to present them.