the cow, the pig, and the horse
When I read that title on the Hot Network Questions list, I thought it was the title of a children's story similar to The Lion, the Witch, and the Wardrobe by C.S.Lewis.
But the characters of the story do not each represent a category but rather the singular animal, the female with supernatural powers, and an inanimate piece of furniture. If there had been more than one lion and witch, the story would probably have been titled: The Lions, the Witches, and the Wardrobe
When we speak about a representative of something or something, we often do use the singular with the definite article.
- The lion is a beast that often lives in the Savannah.
The lion is a well-muscled cat with a long body, large head, and short legs.
Source Britannica
The cow is a ruminant, and cow's milk has evolved to promote bacterial growth in the upper small bowel; whereas human milk has evolved to discourage bacterial growth.
Source: The human rumen by A A Jackson, M H Golden
When talking about inanimate things or animals in general, we use the plural form. The use of the indefinite article a, in a pet pig, suggests “any pig that is kept as a petâ€.
- In recent years, the intellect and friendliness of pigs have been re-evaluated and appreciated. The number of families that has a pet pig in the home, especially in the country, is no longer perceived as being peculiar.
The plural applies to all sorts of animals, including pets and farm animals.
- Children visitors can see how cows, sheep, pigs and horses live on a farm and how they are looked after.
English native speakers will always omit the definite article in speech.
- My friend's farm has [got] cows, pigs and horses.
- There are only three kinds of animals living on my friend's farm: cows, pigs and horses.
Using the definite article (the) would sound academic and rather pompous because we're talking about a friend's farm, not about a breed, e.g. The Great Dane is an extremely large domestic dog… or a particular species.
The following examples may be grammatical but they do not reflect natural speech in English.
- My friend's farm has the cow, the pig and the horse.
- There are only three kinds of animals living on my friend's farm: the cow, the pig and the horse.