Cattle

Cattle were domesticated mammals native to Earth. Females were called cows. (DW: Image of the Fendahl) Clyde Langer once succinctly said – while he was looking after baby Sky – that "cows eat grass, and they make milk and they go moooo... [and] they also make steak." (SJA: Sky) Indeed, Rose once suggested to the Ninth Doctor that being out of cow's milk was a part of the reason that they often ended up back on Earth. "All the species in the universe," the Doctor replied, "and it has to come out of a cow." (DW: The Empty Child)

Encounters with cows
The Doctor and his companions and acquaintances occasionally dealt with cattle.

The Doctor
After materialising in a field, the Second Doctor and companions turned on the viewscreen to see the face of a curious cow staring at them. (DW:The Invasion)

The Fourth Doctor once landed the TARDIS amongst a herd of cattle and facetiously asked them if they had a time scanner, to no avail. (DW: Image of the Fendahl)

The Eighth Doctor also liked to talk to cows. After he and Destrii defeated the Cybermen, he landed the TARDIS in a pasture. He then began talking to the cows and telling them what a great day it was to have saved the universe. Upon noticing that he had lost his frock coat in the preceding battle, and Destrii suggested that he would look good in leather (she was wearing a black leather jacket at the time). The Doctor then noted that Destrii was once again "charming the locals", ostensibly indicating that leather came from cattle. (DWM: The Flood)

On another occasion, the Eighth Doctor (who was then split into three bodies), Charley and C'rizz encountered cows in the Garden of Curiosities. This meant that cattle existed not only off-Earth, but in completely different dimensions. One of the three Eighth Doctors noted that cows could become dangerous if they grouped together and stampeded. He seemed particularly worried about cow hooves during a stampede. (BFA: Caerdroia)

The Sixth Doctor and Peri witnessed the heavens open up to dump cows on the beaches of Ostend, Belgium. (BFA: Year of the Pig)

Companions
When she was briefly a vampire, Nyssa feasted on the blood of a cow in the fields outside Manchester in the 1990s. (MA: Goth Opera)

Bernice Summerfield once experienced a freak time anomaly in which leather shoes were turned back into cows. However, the time anomaly only restored the cows a point shortly before they were turned into leather. Thus, the floors of the Gigamarket were littered with dead cows. (BFBS: The Greatest Shop in the Galaxy)

Others
Dr Scotus, a veterinarian working near Cardiff, once examined a cow that had begun eating other cows, because it had been affected by an alien tapeworm which had come through the rift. (TWN: Slow Decay)

Even the Doctor's enemies used cows. Zygons once used body-print technology to take the form of cows as they were allowed to roam freely. As was necessary for the proper operation of body-print technology, the Zygons stored the real cows in their ship. (NSA: Sting of the Zygons)

Once humanity became a space-faring race, they took cows with them to the stars. As Earth's influence spread, cattle were shipped off the planet across the galaxy, such as Jadea. (EDA: Placebo Effect) Humans also brought cattle to Sarath. (PDA: City at World's End)