Actually most ethical zoos advise AGAINST doing this, such as myself. The optimal time to begin any sexual activity with a female canine is on their second heat cycle which usually happens at around 1.2 to 2 years of age depending on the breed. Some go as far as not advocating sex until the third heat cycle. It's important that on the first heat cycles that you merely comfort the dog because she's still a puppy and the first heat is a confusing and sometimes scary time for them. You should also never train a dog for sex. You don't need to, just look up "sexual imprinting" and that will tell you all you need to know. It's actually quite common for female animals to lust after the human partner they feel comfortable with.
Some people are allergic to a male animal's semen. Outliers exist, you know? It's funny that I've managed to cum inside of my female canine well over 400 times now and never had an issue. That's pretty typical. A female canine has ways of removing the ejaculate from her vaginal cavity. The sperm will immediately separate from the semen, the "waste" semen will be leaked, pushed, and peed out. The unused sperm (since it's impossible for humans to impregnate a female nonhuman animal) will be absorbed into the mucus lining the vaginal and uterine wall, broken down, and expelled from the body as waste, usually in the form of urine.
I'm more attracted to canines than I am to humans. I didn't form a close bond with my animals because I couldn't "find a suitable human partner," I myself am zoosexual, which is a sexual orientation. I've actually turned down many women over the years. You also forget that there are many zoo-exclusive people on this board. They literally have no attraction to humans whatsoever, and for some the human body is downright repulsive to them. Nonhuman animals are not a "replacement" for human love. It's literally what we are sexually/emotionally attracted to.