Yes. You are both correct here. But both examples are within the same species , I mentioned horses and donkeys, but not cows and buffalo.
Canis and bovinus.
I'm pretty sure too you can add Yaks and Water Buffalo and Oxen to ranks that can be cross-bred with cows as well. It would most likely take lab conditions due to size differences, but you could also add Chihuahua and Wolf to the list of animals in the cross-breeding possibles as well. For that matter, Teacup Poodles
To piggyback off of
@SxaBeast linked material, I type hybrid biology into the search bar and got the following page.
en.m.wikipedia.org
And below, from the above link, I lifted via cut and paste the entire 2nd paragraph from that page.
Species are
reproductively isolated by strong barriers to hybridisation, which include genetic and morphological differences, differing times of fertility, mating behaviors and cues, and physiological rejection of sperm cells or the developing embryo. Some act before
fertilization and others after it. Similar barriers exist in plants, with differences in flowering times, pollen vectors, inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and the structure of the chromosomes. A few animal species and many plant species, however, are the result of
hybrid speciation, including important crop plants such as
wheat, where the number of chromosomes has been doubled.
In my cut and paste, the bolding is NOT mine, but represents Hot Links from that page to those specific topics.
There is also plenty of circumstantial and recently, physical evidence of Modern Human and Neanderthal hybridization/cross-breeding.
Further, if you follow such information, you may have seen speculation in recent years after the discovery of fully intact Mammoth remains in Siberia of reviving the Mammoth species. Though if I remember correctly, the talk wasn't primarily of hybridizing but of straight up geneticly replacing the DNA in an elephant egg with Mammoth DNA and using an Elephant cow to bring the revived Mammoth baby to term. I didn't dig down into the technology of that but that's the general gist of it.