Can cows survive on grass alone?

This is the response that I always get when they inquire about my job from family members and fellow travellers at airports. Many people still believe dairy cows eat hay and grass on their own. In a green pasture next to a red barn, they have the idyllic picture of black and white cows outside.

While some cows on grass alone can support many of their needs, they are usually non-lactating cows (i.e. cows that do not produce milk). There is a high metabolism of a lactating dairy cow and it is very similar to a marathon runner or high-performance athlete.

Dietitians for Cows Milk

With a few sprigs of broccoli, a modern dairy cow consuming grass alone would be equivalent to a marathon runner or Olympic athlete consuming only lettuce. Everyone had a couple of cows back in the old days, and they only wanted to make enough milk for their family.

Every day, the modern dairy cow now makes about 10 gallons of milk. A modern average lactating dairy cow would eventually lose tremendous amounts of weight and be unhealthy on grass alone. As a dairy cow nutritionist, while producing healthy nutritious milk, I ensure that cows have all the necessary nutrients to perform and stay healthy.

The diet of a typical dairy cow is about 50 percent forage and 50 percent grains. Most of the forages are plant material, known as silage, that is fed as hay or fermented forage. This enables farmers to feed year-round grass, legume and corn-based forages. Maize and soybeans are the most commonly fed concentrates, along with by-product feeds such as whole cottonseeds, citrus pulp, almond hulls, or soy hulls. In their diets, cows enjoy variety, and having a mixture of both forage and concentrate allows this. We must provide the correct amounts and balance of nutrients, just like with human nutrition.

In that, cows are distinct from humans:

Cows have a stomach with four compartments and a large fermentation vat. This vat of fermentation is referred to as the rumen. Bacteria in the rumen assist in digesting the feed. This allows cows to obtain nutrition from feed containing cellulose and fibrous material that is not possible for humans and other animals. This is one reason why a lot of by-product feed can be consumed by cows.

The choice of feed that is offered to them is limited to cows. Nutritionists formulate their diet, and one mixed casserole, called a total mixed ration or TMR, is offered to them. Cows can be picky, however, and they will attempt to sort through the feed offered to them. Like humans, some foodstuffs are preferred to others.

Cows have the ability to ruminate as well. They eat their meals rather quickly, and then they will further digest the feed that has been consumed while resting. A ball of feed, known as a cud, is regurgitated and then they chew on that cud. This makes it possible for them to break the feed into smaller particles. It also generates saliva, which helps to prevent the rumen material from becoming too acidic and causing indigestion.

I do have some advantages as a cow nutritionist that I’m sure dietitians would appreciate. Based on records of what was consumed, I can check diets, chemically analyse that diet, and alter it accordingly… and my customers (the cows) will usually accept my recommendations. To be honest, cows eat a better diet than people!

As you can see, there are many similarities and a few key differences between a cow’s nutritional requirements and a human’s. Cow nutritionists have a common objective with human dietitians: to provide our customers with a healthy, balanced diet within a budget.

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