In A Nutshell
Even the short answer is a bit complicated: Oxen and cows are both cattle, but not all cattle are cows and oxen. The umbrella term for the animal is “cattle” (or bovines), while cows and oxen have specific roles beneath that umbrella. Oxen are working animals, while cows are female animals kept solely for their milk or meat production and breeding potential.
The Whole Bushel
Cattle is the term that covers all bovines, regardless of age, gender, and purpose. Interestingly, recent DNA studies have concluded that the roughly 1.5 billion cattle that populate the world as of 2013 came from not only the same area—modern-day Iran—but from the same small herd of about 80 animals. These animals were a creature (which is now extinct) called the aurochs, a type of wild bovine much larger than most of today’s cattle. While they once stretched across Europe, Asia, and northern Africa, they were also widely hunted and numbers suffered greatly from forced competition with domestic animals. They were slowly driven to extinction, with the last specimens dying in Poland in 1627 after failed attempts at preservation by the royal family.
While there were once countless herds, it’s thought that only the single Iranian herd was ever domesticated because of the simple idea of mobility. Most early humans had a more nomadic lifestyle than cattle breeding would allow for; peoples in the Middle East who had settled in permanent areas were able to selectively breed the aurochs and create the basis for the breeds we know today. By the time keeping of cattle spread, there was already a marked difference between the wild aurochs and the domesticated cattle.
Oxen exist beneath the umbrella of cattle, and are animals that have been trained to work either in the fields or pulling things by yoke and collar. Any breed of cattle can be trained to be an oxen, but generally larger, stronger animals are selected. Oxen are typically male animals, as they rely on their size and strength to do their jobs; also, large horns play a role in the ability of the oxen. When the animal backs up, the large, sturdy horns keep the yoke from coming off over their heads.
While any cattle can be an oxen, some breeds or individuals are better suited to the task. In addition to size and strength, those looking to train oxen also look for intelligence, a willingness to learn, and how personable the animal is.
Oxen generally end up being some of the largest specimens of cattle, but that’s not because of breed. Most male cattle not selected for training (or breeding) are killed for their meat before they reach full size. Continued training of oxen also helps build muscle mass and overall size; horns will continue to grow for the entire life of the oxen. A team of oxen thought to be among the largest ever bred were Granger and Mt. Katahdin; these 1930s Maine oxen tipped the scales at a combined 4,450 kilograms (9,800 lbs) when fully grown.
Cows are female cattle that have had calves or are over 2.5 years old. (Younger female cattle who have not yet given birth are called heifers.) In many agricultural areas, cows have historically and frequently been trained to work as oxen. This way, the family has a single beast that can not only plow their fields, but reproduce and supply milk. Also, cows can still be bred while being used in the role of oxen, allowing the farmer to choose working replacements born from his own animals rather than buying new males (which would be used only for training) to replace the current working team when they age beyond their useful years. Cows that serve more than one purpose generally stay smaller than oxen, but can be more efficient in the end for small farmers.