I Found some of these articles
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All women can feel a knot thru their tummy with their hands, and a lot of women, especially petite ones (like me) can visually see their knot 
A dog cums directly into a girls womb thanks to their pointed cock which creates a warm, full feeling inside girls which often contributes to the intense orgasms, while men's cock which is curved away from the cervix makes it impossible for a man to ejaculate in a girls womb directly.
Dogs ejaculate far more volume than necessary to totally fill the womb and it often results in very visible belly swelling that stays there for hours or even days. the remaining cum often drips out the cervix and needs girls to wear maxi pads (I have been doing this even tho I'm not on my flow), and the rest is absorbed by the body
Dog knots directly stimulate the gspot which creates a state of high, consistent constant pleasure for a girl the heaven-like state is punctuated by often dozens of earth-shaking orgasms
Dog cum is very beneficial to women. The chemicals and hormones inside the cum makes a girls vaginal walls thicker, stronger and more sensitive, and the womb far more fertile for a dogs sperm. It also makes a slightly alkaline environment in the vagina and womb which makes it far harder for a man to knock her up and your pussy far more hospitable to a dogs sperm. It also rejuvenates a woman and makes her pussy tighter and younger, tightens her breasts and make them more perky, make all your skin look younger and glow, and can even make wrinkles disappear...just from having him ejaculate in you!!
Dogs have around 900% MORE sperm cells per drop of semen compared to the most fertile men which is an astounding feat considering the amount of ejaculate they make!
Dogs ejaculate 8-16 BILLION sperm cells in a single orgasm. The most fertile men ejaculate 300 million
The average penis size for a large breed dog like a great dane, German Shepherd, husky, Labrador, etc. is 9 inches long and 6 inches of girth
The average testicle size for a large breed dog is around the size of eggs, or around the size of both an average man's testicles combined into one.
A dogs makes enough sperm in 8 hours to impregnate every woman and girl on the planet twice
If a dog were able to impregnate a woman it would take an astounding 24 seconds at least and 30 seconds at average to impregnate her. If you were to look at the egg while fertilization were occurring the egg would be completely engulfed in billions of sperm thanks to dogs ability to ejaculate directly into the womb. Meanwhile men lack that ability and when fertilization is occurring with humans there are only a dozen or so sperm on the egg and it often takes several hours, sometimes even a day to impregnate a girl.
Dogs cocks, testes (surface), semen and precum are full of hormones that after prolonged exposure create a long term craving for more sex from the dog and make women able to be much wetter and hospitable to sperm
Also when a woman is active and exposed to the stud and his charms and hormones, the level of stimulation is much much higher than with a man and the hormones really drive a woman to want more k9 cock..very primal need.
What K9 women are feeling is the very deepest sexual desire without the clutter of procreation and other complications..makes for a very wanting bitch for a k9 stud.
A doctor on BF explained to me what is happening inside a girls body when a dog is fucking her...
"I'll run through what is happening during the sex activity with a large breed male dog from the beginning to finish. He slides it into you and you feel a large spike of pleasure and stretching. This spike in pleasure which remains the constant level of pleasure while he is in the thrusting/fucking you stage of a sexual encounter with a human girl, is both the higher temperature of his cock as well as the new, foreign texture you feel of his cock and knot. Even after fucking a dog for many many years the texture and heat will always feel extraordinary and foreign. The hardness is also an awesome contributor to the pleasure because it is different than what you've felt before since a dog cock can hold more blood and also has a bone making it feel very hard with no possibility of erectile dysfunction unlike what a large amount of men experience. The hard pounding being so fast and dominating is an exclusively dog/k9 experience. No man can keep it up while his body is absolutely designed for it. Meanwhile he's lubing you up with pre-cum..around 8 ozs. or so. Your pussy literally absorbs the new stimulant and your estrogen goes thru the roof and his system reacts to that and he starts making lots of testosterone to peak your pussy. You feel it as an itching then warming sensation as you start to spasm he drives his cock deeper and deeper, still making precum in you and and as that happens you start to feel him hitting you deeper as your estrogen and his testosterone continue to rise making your pussy wetter and deeper. And then you're really feeling the urge to take him deeper, opening up for his cock and knot combo and having a strong powerful orgasm as you do...hormonal levels are rising rapidly and you instinctively push back into his cock, a reflex from a craving of more of his incredible sex. He stops a full thrust deep inside you and his pointed cock meets your cervix making what zoo doctors like myself call a "cervical kiss", and his pointed cock creates an efficient entry point for his many billions of sperm cells. His knot continues to grow and you squeeze his knot as you spasm hard and he responds by pumping you full of his incredibly potent seed. His pumping action is far far stronger than any man and you will definitely feel it as it is very very prominent, with each pump of semen making his cock nearly 50% thicker which creates spikes of pleasure with every pump. You feel his warm cum and bang you start shaking as it hits you and cumming harder as he loads you and his knot swells slightly more in response to your powerful orgasms to seal your pussy so as not to lose his valuable load..your mind is likely in a state of total pleasure by now and you essentially stop thinking as you are totally washed over by pleasure. You put your face into the bed and your ass higher in the air as your estrogen levels are at an incredible rate which make you submit to the alpha at least 10 inches deep inside you. After often an hour but sometimes many hours of prolonged intense incredible pleasure and ejaculation, his knot finally shrinks to the same girth as the rest of his penis and he slides out, with a large plop sound and a wave of semen coming out. The semen that comes out immediately after his pullout is the small amount of semen he makes that does not make it into your womb. Something I find very funny is that even the very small volume that does not make it to the womb is often far larger than most men's total volume of ejaculate!
It astounds me that very very very little money has been put into more research on this in the name of stupid traditions and prejudice as it is very clear by my and my colleagues research and women's experiences that this is a VERY beneficial hobby, which inevitably and often becomes a full-time occupation. I hope someday that this prejudice will end so we can put more funding into discovering and studying the power sex with a dog has on a woman, and hopefully one day we can genetically manipulate a dogs testicles to create human sperm cells that would make it possible for K9 breeder women to finally fulfill the deep craving their hormones are giving them to be impregnated by their K9 lovers. This would be the best thing science could do to help zoosexuals in their sexual exploitation as it would not make half dog half human monstrosities and it would also likely make global headlines and spike female interest in their furry pseudo-stud friends and create a large amount of girls curious about their dogs."
Another doctor added "Well it goes with being a newbie and being overwhelmed at first in a sexy,oozing powerful fuck beyond anything you've had before..and it gets better the more you breed and learn to bitch for him..lots more rewards cumming your way..sexually you will never be the same..better but not the same..you will learn how much you lust to breed and find yourself living and working around your new interest and sexual companion...you find dog cock is a real treasure and treat to protect and in some cases you'll worship how it makes you feel..just my $.002"
That's just what I've discovered in 3-4 days I am sure I will find more!! 
Oh I forgot: benefits outside of normal human-human sexual pleasure a woman gets from a man's sperm:
Can get knocked up
