Why Do Cows Eat Grass? (Explained, Facts and Answers)

Why Do Cows Eat Grass

Cows can graze up to 12 hours a day is a testament to the terrific affection these ruminants have for grass. But why do cows really eat grass despite how unattractive it may look to you?

Grasses are massively nourishing for cows. Comprising vital nutrients like protein, fiber, minerals and energy source, grasses form a staple diet of a cow’s diet. Given that cows are ruminants, they have multiple stomachs (rumen, reticulum, omasum, and abomasum) well-adapted to breaking down the grass, extracting the nutrients for the cow’s sustenance.

From the endless grazing to the curious chewing of cud, there is an interesting lot to learn about cows and grasses. You may have wondered: can cows survive on grass alone? Are grasses delicious to cows? How much grass does a cow consume in a day? Relax, I will be answering these questions with authoritative revelations in this guide.

Do Cows Need to Eat Grass?

Grasses pack a bulk of vital nutrients for cows. Basically, grasses contain dry matter and water. For context, an estimated 83kg of water can be found in 100kg of grass.

The dry matter is generally constituted of essential nutrients like protein, minerals, fats, and sugar. These are highly nourishing for cows.

The dry matter is comprised of cell content and cell wall. Specifically, cell content includes the likes of sugar, minerals, and proteins. Cell wall predominantly consists of fiber.

While the likes of pigs will struggle to extract any nutrient from grass, the cow’s digestive system is biologically streamlined to digest grass and extract nutrients the cow needs to thrive.

How Do Cows Get Energy from Eating Grass?

Cows derive massive loads of energy from the grass they eat. Basically, this energy is processed from the fiber and sugar contained in the grass. The quality of the fiber also determines the amount of energy the cows extract from the grass.

A fraction of the proteinaceous and oil content of grass is still processed into energy in cows. Leafier grass is more energy-providing for cows.

Specifically, cows are more energized when they feed on grasses where the leaf composition exceeds 80%. This is why farmers aiming for higher performance in their cows feed them high-leaf-content grass.

Grasses with more prominent stems (compared to the leaf) are not as energizing. Specifically, increases in the stem content make the grass less digestible for the cow.

Don’t forget that the energy nourishment of the grass also depends on the season. Expectedly, you may have an energy content of 0.8 UFL / kg DM (where UFL is the energy composition of 1kg of standard air-dry barley) for grass with prominent stem proportion in autumn. But you may get as much as 1.05 UFL / kg DM for grasses with a significant leaf proportion in spring.

Can Cows Live on Grass Alone?

Yes, cows can survive on grass alone, but this is not ideal. Most times, the nutritional sufficiency of the grass depends on the cow’s state and the season.

A cow that is not producing milk (particularly calves, suckler cow, and yearlings) may have its nutritional needs met by a grass-only diet. However, lactating cows would need more than just grass due to their increased metabolic rate.

This necessitates such grass-based diets supplemented with additional mineral provisions like copper, cobalt, selenium, and zinc. Protein and salt are also nice supplements for grass when feeding cattle.

The season also affects the nutritional content of your grass, ultimately determining whether the grass would solely suffice for your cow. Extended winters and long dry summers often trigger significant diminishment in the nutritional content of hay.

In such periods, cattle should be fed more than grass to keep them adequately nourished. High-protein corns and molasses are particularly beneficial for this purpose.

A cow’s supplementary protein needs can also be assuaged with legumes like crimson clover and cowpeas in the summer. When winter comes, you can resort to hairy vetch to supplement your cow’s protein needs.

The question we are asked often is how do you know if the forage you feed your cows adequately meets its nutritional needs? A good means to ascertain this is by leveraging a soil test of the area your pasture is sourced from. Such a test will point out if your soil is low in vital hay mineral nutrients like sulfur, selenium, and zinc.

What is Called When Cows Eat Grass?

When cows eat grass, they are to graze.

Does Grass Taste Good to Cows?

We can’t authoritatively confirm if cows find grasses delicious. Nonetheless, we can at least say cows have shrewdness for discerning between which grass they find attractive and edible and those they don’t.

Do Cows Get Protein from Grass?

The cow’s digestive faculty can process a significant amount of protein from the grass it chews. Factors like growth stage (of the grass), sward type, season, and fertilizer application determine the protein content of grass for cattle.

By standard, the protein content in grass ranges from 16-28%. In rare cases – especially when there is drought or sustained stress on that particular grass plant – the protein content can fall as low as 11%.

Why are Cows Fat if They Only Eat Grass?

Cows can add weight if solely fed with grass. This is because of the substantial nutrients the cow’s digestive system can derive from grass.

How Much Grass Will a Cow Eat Per Day?

As said, a cow’s dietary intake depends on its condition – whether it is ill or healthy, pregnant or not, young or old. For example, let us take a pregnant cow of about 1,000 lbs reared in a spring calving system.

If the fodder quality is good, such a cow will typically eat 2% of its body weight in a day, which will be 20 lbs. When cows graze, they eat forage (typically grass) till they are full.

When they feel food, they resign to chewing their cud. Given the fact that cows are avid eaters, you should be worried for its health if it doesn’t eat in a day.

What Grass is Bad for Cows?

When it comes to grass, cows are not the most selective. Cows eat a wide spectrum of grass, ranging from bluegrass to fescue and orchardgrass. However, there is a tiny cluster of plants that should never be fed to cows, given the tendency of such plants to poison your cow.

Lupines and water hemlock are two plants that you should diligently keep from your cow’s forage. The thing about lupine is that they tend to dominant typical cattle-healthy grasses during the cool, wet springs.


In early springs, low larkspur is a nuisance for cows, while tall larkspur can be especially dangerous to your cows during mid-summers. There have been several cases where storms force cows into grazing areas dominated by tall larkspur.

This has unfortunately led to large-scale cattle poisoning. Aside from the said plants, other poisonous counterparts (for cows) include death camas, nightshades, and poison hemlock.

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