Why Are Cows Fat?

Cows are fat for two main reasons. Firstly, storing fat is an evolutionary advantage for grazing animals such as cows, and secondly cows have been selectively bred to increase their body weight over time, for increased beef production.

In this article, we’ll be looking at cows’ body weight, learning exactly how fat they are, how they manage to get so large when all they eat is grass, and how they compare to other large animals.

Why Are Cows Fat

How Fat Are Cows?

On average, a typical US beef cow weighs around 1200lbs, or 600kg. 

According to data from the National Center for Biotechnology Information, the average beef carcass in the US is made up of between 35 and 50% fat by weight.

Using NCBI information, we can work out that cows are between 35-50% fat which equates to up to 600lbs (300kg) of fat for the average 1200lb cow.

How Do Cows Get So Fat When They Only Eat Grass?

Although cows mostly eat grass when they are out in the pasture, their diets are commonly supplemented with grains like corn and barley, soy, and hay.

It’s these additional grains, combined with selectively breeding cows to select for body mass which leads to the over-sized cows we see on modern beef farms.

Is Grass-Fed Beef Less Fatty Than Grain Fed Beef?

In general, grass fed cattle are less fatty than their grain-fed counterparts. 

In comparison to regular cattle which have their diets supplemented with corn, soy, or other grains, grass fed cattle are leaner, owing to them having to forage over a wider area to find enough nutrients.

Dietary grain supplements are designed to fatten the cows up as quickly as possible to maximize profits for the farmer. Grass fed cattle are leaner and more muscular and this carries over to the beef produced from these animals too.

Why Are Cows So Fat?

Cows are fat for two main reasons, one natural and one man-made.

1: Storing Excess Energy as Fat was an Evolutionary Advantage for Cows’ Ancestors.

Cows are naturally large animals which are biologically conditioned to store excess energy as fat. In the wild, bovine species are migratory, moving with the seasons to ensure they constantly have fresh pasture land to graze on as they deplete their current location.

As an example, Wildebeest in Africa take part in a huge, circular migration every year known as the Great Migration. Their annual route covers three countries and follows the wet season around. Over 250,000 wildebeest die of starvation and predation every year during the migration.

Read More: Buffalo vs Cows – What’s the difference?

Cows’ ancestors followed similar migration patterns as modern wildebeest and buffalo, meaning it was an evolutionary advantage for them to store as much energy as possible as fat in the good times to see them through the hard times and stave off starvation.

2: Cows Have Been Selectively Bred to Maximize their Body Mass

Cows were first domesticated over 10,000 years ago, and ever since that time humans have been selecting cows based on their usefulness to us.

Beef cattle are selectively bred to ensure the maximum possible beef yield in the shortest possible time, meaning cows today are faster growing, and larger overall than their natural ancestors.

Read More: How Long does it take to Raise a Cow for Slaughter?

Are Cows The Fattest Animal?

Cows are pretty fat as far as land mammals go, but to find the fattest mammals you need to look to the ocean. 

The fattest animals are aquatic mammals like seals, walruses, and whales, since they need their fat to swim huge distances and protect their warm blood from the cold ocean.

Cows are not the fattest animal, or even the fattest mammal. The animal with the most fat in terms of both total mass and as a percentage of their body weight is the blue whale (Balaenoptera musculus).

Are Cows Fatter Than Horses?

According to Shannon Pratt-Phillips MSc, horses typically have up to around 14% body fat. This is considerably less than beef cattle, who can have up to 50%, so cows are fatter than horses on average.

Are Cows Fatter Than Goats?

Cows are significantly fatter than goats. In recent years, goat meat has been making a revival in the US and Canada precisely because it contains less fat than beef, pork, and chicken.

Are Cows Fatter Than Pigs?

According to the National Center for Biotech Information, both Cows and Pigs share a similar body fat percentage of between 35 and 50% body fat.

In total volume of fat, cows are fatter because they are much larger.

How Do Farmers Fatten Up Their Cows?

Farmers have a vested interest in making sure their cows get as fat as possible, as fast as possible, so that they can get the best price for their cattle while minimizing the length of time they need to feed them.

Farmers fatten up their cows by supplementing their natural forage diet with grains such as corn, rye, or barley, or with soy or alfalfa grass in the form of hay or silage. This helps the cow grow to full size within a couple of years. Most beef cattle are sent for slaughter at about 3 years.

Fattest Type Of Cows

The fattest breed of cattle is the Chianina breed, which originates from Italy.

Chianina cattle can weigh up to an unbelievable 3,500lbs (over 1600kg) and can reach a height of over 5 ft 9 inches tall (180cm).


To sum up, cows are fat for evolutionary reasons, and because they have been selectively bred by humans for thousands of years to increase their size and weight.

Modern cows have a huge energy requirement because of their large body mass, so much so that they often need their diets to be supplemented with grains to help them grow quickly.

The fattest type of cow is an Italian breed called Chianina, which can grow to 3500lbs (1600kg).

Cows are fatter than many other land mammals including goats and horses, but the fattest animals in the world are aquatic mammals like seals, orcas, and whales. 

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