Field Notes: Why are some cows horny? The structure and function of horns

Hornless cattle of different colors graze in a field. (Photo by Alycia Drwencke)

If you’re driving through the foothills of California, you will likely see lush rolling hills speckled with lots of cows! If we look closely at these cows, we can see physical differences between individuals. They may be a different size, or color, or they may have horns while others do not. While most people may not ruminate on these thoughts once they pass by the cows, I find these differences fascinating because even though cattle share ancestors, they have evolved many unique traits. As a first year PhD student, I have had the opportunity to dive more deeply into the presence or absence of horns and how that influences cow behavior. At the beginning of any research project, it is important to gather all the existing information surrounding your study topic. For me, this has meant spending hours upon hours reading and thinking about cow horns. Throughout this reading, I have learned some cool facts that have inspired several research questions focused on horns. As I plan for my next experiment, (and since cow horns are so fascinating), I wanted to share some of the information I’ve discovered and how it will inform my future research. 

 A longhorn cow with horns swooping down from their head. (Photo by Alycia Drwencke)

Horns are structures that grow on the heads of some animals, such as goats, cattle, big horn sheep, and buffalo. Horns should not be mistaken with antlers though, which are what grow on the heads of white tail deer. They are structurally different; antlers are made of solid bone, while horns are made of bone and keratin. Keratin is the same material that your fingernails are made of. For cattle, the formation of horns begins when the calf is developing. When a calf is born, it has small horn buds (about the size of pea) on top of their head, just above their ears. Around 8 weeks of age, cattle horns attach to their skull and grow from a small bump into more prominent horns. As cattle grow, their horns also increase in size. Interestingly, horns on cattle are not solid all the way through as you may imagine. Instead, horns have a hollow center that fills with part of their sinus cavity, blood vessels, and nerves as they age and continue to grow (see photo below). Among the cows that do grow horns, there can be a wide variety of shapes, sizes, and length of horns. The different appearance of horns can be influenced by the breed of cattle and their age.

An illustration showing the anatomy of a cow’s horn. (Adapted from Meat and Livestock Australia 2007, provided by Dr. Sarah Adcock

Cattle have evolved to grow horns for two primary reasons. First, some types of cattle can use their horns to help them stay cool in hot weather. Second, cattle can use their horns when interacting with other animals or humans for resource competition and defense against predators. When interacting with other cows, they can use their horns as a tool to help them defend access to the best patch of food or other desired items. An individual with horns has an extra tool they can use for defense compared to a cow without them. Horns can also be used to scratch itches in hard-to-reach spots on their back. Since horns are made of bone, they are very tough and can be used for self-defense when needed. This comes in handy for cows that are trying to protect their babies from other animals or danger. Similarly, humans can sometimes be mistaken as danger, even if the individuals’ intentions are positive.  When interacting with other animals or humans, horns can be used as a warning sign to back up and give the cow some space. If a cow directs their horns towards you, snorts, and paws at the ground, it’s time to back away and leave them alone so you don’t discover just how tough those horns are. 

A longhorn cow with horns that stick up and twist around in shape. (Photo by Alycia Drwencke)

In addition to the usefulness of horns for the cows, many cultures have found a deep appreciation for the beauty of them. In fact, some cultures place a high value on cows with very large or unique horns. A good example is the Texas Longhorn. These cattle have become a recognizable symbol across the U.S. because of the cultural importance that has been placed on their very large horns. With such high regard for size, humans have chosen to breed cows specifically for this trait. Similar to how some breeds of dog are bred for their calm nature, or their listening skills, Longhorn cattle are bred specifically for their enormous unique horns. This value and admiration for unique cattle horns is consistent across cultures around the globe. For example, in Africa the horns from the Ankole-Watusi cattle are revered by locals for their remarkable shape and size.

 Dairy cattle that had their horn growth prevented early in life. (Photo by Alycia Drwencke)

While not all cows have horns there are several reasons why this may be. Some cattle are what is called a “polled breed”, which means they naturally do not grow horns. This is common in cattle that are raised for meat. However, there are also cattle that are born with horn buds, but these buds are prevented from developing further. In these situations, the cattle have had a procedure done called disbudding. This procedure is performed on 94% of dairy cattle in the U.S. [1] and prevents a calf from having its horns develop from the small buds into larger horns. In the U.S. this is done within the first 8 weeks of life with either heat or a paste to stop the horn growth. Farms may choose to prevent a calf’s horns from growing for a few reasons. One is that when cows are raised for milk production, they are brought into a parlor two or three times per day. In the parlor, the cows are in close contact with each other and milking equipment. Horns can make it difficult for cows to maneuver around in the milking parlor, providing incentive for some farms to raise cattle without them. Additionally, some farms prevent the horns from growing for safety reasons, so cattle cannot accidentally injure each other or the workers. My PhD research is focused on understanding the cows experience when their horns are prevented from growing by assessing their behavior before and after that procedure. 

Horns are a fascinating attribute for cattle, from the unique size and shape of them to the way cows can use them for specific behaviors.  Even the absence of horns tells a story of prior human interactions with those cows. So, next time you drive down the road, keep your eyes peeled for the cows and see if you can spot the differences between the horned and hornless cattle.

A beef cow that was born without horns. (Photo by Alycia Drwencke)

References:

[1] USDA. (2022). Dairy 2014, Health and management practices on US dairy operations, 2014.

Alycia is a PhD student in the Animal Behavior Graduate Group at UC Davis in Dr. Cassandra Tucker’s lab. Her research examines the behavior and welfare of dairy calves during routine care. Alycia’s research is focused on continuous improvement in the dairy industry while maximizing dairy cattle welfare. 

[Edited by Josie Hubbard and Maggie Creamer]

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