Yak

Yaks are a common background animal on Berk and seen across various Franchise media.

Description
Yaks (Bos grunniens) are woolly, shaggy large mammals with a pair of horns. They have cloven feet. They are in the bovine family, making them related to cattle, bison, buffalo, and others.

Oddly enough, a Yak makes an appearance in the movie short, Book of Dragons, and is being shoed. In actuality, Yak are not shoed like horses, and have cloven feet, not a single, hooved toe like horses.

Behavior
Yaks are quiet animals that were terribly afraid of dragons when they invaded Berk. These large mammals are often found slowly grazing grass at on Berk. They do not have many talents or abilities, however, they are known to be able to run at fast speeds when escaping danger. When they fall down, they are unable to stand up again. This makes them an easy target for dragons to hunt.

Function
Yaks appear as a substitute for cattle in the How to Train Your Dragon Franchise. These livestock are used for their milk, meat, and hides. A seasonal Snoggletog 'treat' is made from Yak milk, called Yaknog. Another yak dish mentioned in the Franchise is Yak Noodle Soup. A Farm Job in School of Dragons implies that Snotlout created strawberry milk. Another Farm Job mentions Arctic Poppy, along with Dragon Nip and Yak milk combined into a stew for dragons.

"Fishlegs has cooked up a popular stew for dragons. Time to restock!"

- School of Dragons

Milk can also be used in medicine, as seen in a School of Dragons Farm Job asking for yak milk, Toothache Plant, and Arctic Poppy to treat a dragon's toothache.

Presumably other parts are used such as their bones and horns, as well. Their whole heads might be mounted on the wall as decoration. In the Game, How to Train a Dragon, the Night Fury's favorite food is Beef. Yak are also seen in the Franchise as beasts of burden and as pets.

In actuality, in addition to the above, they are also used for riding and sport. The meat of the Yak may technically be called "Beef", as Beef is the meat of "cattle". Cattle most often refer to (Bos taurus), but can sometimes refer to other domesticated bovine species, such as yaks.

"Cattle, domesticated bovine farm animals that are raised for their meat, milk, or hides or for draft purposes. The animals most often included under the term are the Western or European domesticated cattle as well as the Indian and African domesticated cattle. However, certain other bovids such as the Asian water buffalo, the Tibetan yak, the gayal and banteng of Southeast Asia, and the plains bison of North America have also been domesticated or semi-domesticated and are sometimes considered to be cattle."

- "Encyclopædia Britannica"

Book of Dragons
Yaks are seen very nominally in this movie short. One is seen being shoed by Bork the Bold, as he tried out Blacksmithing as a career.

Dragons: Riders of Berk
In "Animal House"here was a terrible blizzard. Yaks and other animals were returning to Berk village with the Dragon Riders, but as they could not see well, the gang got lost. Terrified of dragons, the animals ran away. Hiccup and the gang then captured them all and the yaks overcame their fear.

In "How to Pick Your Dragon", Ruffnut Thorston and Tuffnut Thorston overturned yaks for fun. The animals were unable to return to their feet.

In "Heather Report, Part 1", Hiccup offered Heather some fresh yak milk. This shows that yak milk is used.

In "What Flies Beneath", Toothless' Rival, a Whispering Death devoured a yak along with several Sheep.

Dragons: Race to the Edge, Season 1
Thor Bonecrusher saved a yak calf from falling off a cliff by jumping in front of it, pinching it and causing it to sleep in "Big Man on Berk".

Dragons: Race to the Edge, Season 3
In the episode "Turn and Burn", the Jorgensons bring a yak with them to Storehouse Island. He is named Yakkity.

Dragons: Race to the Edge, Season 4
In "Not Lout", Snotlout attempts to demonstrate leadership qualities by returning items he had to the Twins. One item was "Fluffers", a stuffed toy yak of Ruffnut's.

Dawn of the Dragon Racers
A baby yak charged at Ruffnut and Tuffnut when they thought that it was the black sheep. There was also a scene in which a Yak head is seen displayed on the wall of a Viking home.

Dragons: Rise of Berk
In the Journey activity for Fishlegs and Meatlug to Forest Island, Fishlegs carries along dried Yak meat to entice the wary Firescrapes with.

There is also the building "Yak Farm" a player places on Berk to increase their Viking population and advance in the Game.

School of Dragons
In the games, School of Dragons, the player has a farm with various crops and livestock to raise and harvest. Yak are one of the animals a player can purchase and harvest milk from. There are various Farm Jobs which require Yak milk for completion. There are also other Quests relating to Yaks - for example the quest "Scrubbed Clean: Part 1" requires the player to obtain Yak tallow (rendered fat) for soap-making. Yak Noodle Soup is mentioned in the Quest "What a Mess!". Astrid asks the player to help make Yaknog in the Quest "Time for Togetherness". Two yaks pulling a cart of supplies appear in "The Simplest of Machines".

Trivia

 * Yak are not native to Scandinavia. They live in central Asia in the Himalayas, and have been domesticated for thousands of years.
 * There is a breed of cow called the "Scottish Highland" that roughly resembles Yaks in How to Train Your Dragon. They are dual purpose cattle with wide horns and long shaggy coats.