When two male
dogsmate with a female on the same day, it's a race to see which sperm cell reaches the egg first and fertilizes it. But if different males mate with the female on different days, she can get pregnant with both. Female dogs release eggs during their heat cycle, which can last two to three weeks. During this time, if they mate with more than one male dog, they may become pregnant with multiple males.
The success of a pregnancy depends on the biology of the female dog and her partner. If the male dog was introduced at the wrong time, fertilization may not occur. A male dog's sperm is viable for nine days after ejaculation, while a female dog's eggs are mature and able to conceive for an average of five days. For a pregnancy to happen, these two viable moments must overlap.
If your dog mated with two different parents of the same
breed, you may not realize that the litter contains a mix of DNA unless you've seen the two matings or they were planned. Poor health or age can affect a male dog's fertility, while infections like canine herpes and brucellosis can cause infertility in female dogs. Female dogs emit strong odor signals when in heat, so entire male dogs can find and mate quickly. Most dogs will be horny for an average of one and a half to two weeks, and ovulation occurs when their vaginal discharge is pinkish red and watery.
If your dog produces a litter of puppies that look like different types of dogs, it's possible that it has mated with more than one male.