1. How Can Cattle That Eat Only Grass Grow So Large?
Why can cattle grow large bodies if they eat only grass? The answer lies in their stomachs. Cattle have four stomachs, and the largest one, the rumen, is home to many microorganisms. These microorganisms break down the fiber in grass, allowing the cow to absorb it as nutrition [1].
Cattle do not eat only grass. For beef production, the feeding method during the finishing stage varies: some cattle are raised mainly on grass, while others are given more grain. Reports indicate that this difference in feed affects the color of the fat, its composition, the taste, and how marbling forms.
However, these differences are not a simple story of "grass is healthier." The impression changes depending on how you read the numbers, and results vary between studies. First, let us look at the fat color, which is visible to the eye.
2. Why Does the Fat of Grass-Fed Beef Turn Yellow?
It is known that cattle raised on a grass-centered diet tend to have subcutaneous fat that takes on a yellow tint [2]. But what causes this yellow color?
NARO conducted a study using castrated Japanese Shorthorn cattle. The cattle were grazed for about 6 months and then housed and fed rice straw for about 4 months. The study found that beta-carotene and vitamin E levels in the beef decreased, and the yellow tint in the subcutaneous fat also went down [3]. The cause of the yellow color is beta-carotene, and a relationship was reported between its amount and the degree of yellowness. Beta-carotene is a component found in grass, belonging to the same family as the pigment in carrots.
In this study, feeding rice straw for about 4 months reduced the yellowness of the fat [3]. This means that even for the same cattle, changing the feed changes the fat color. However, this test was done on castrated Japanese Shorthorn cattle. The same numbers may not apply to all cattle raised on pasture. Besides color, how does the inside of the fat change?
3. Does Grass-Fed Beef Have Different Fatty Acids When Compared Under Equal Conditions?
Beef finished on grass is reported to have higher levels of certain fatty acids, such as CLA, trans-vaccenic acid, and n-3 fatty acids [2]. It is important to note that this comparison is made "per gram of fat."
There are also numbers comparing beef per 100 grams of meat. A review of 8 comparative studies found that n-3 fatty acids were also higher in pasture-raised beef per 100 grams [4]. However, the way the difference appears changes depending on whether the unit is "per fat" or "per 100 grams of meat."
Furthermore, cattle raised on grass have less fat overall. Total fat, saturated fatty acids, and monounsaturated fatty acids were higher in grain-fed cattle [4]. This means the difference per 100 grams of meat also includes the difference in the amount of fat. The review notes that if you eat slightly more grain-fed meat, your intake of long-chain n-3 fatty acids could end up being similar.
In some cases, the conclusion reverses depending on the breed. For Hanwoo (Korean cattle), one report found that grain-fed cattle had more EPA and DHA. The review cites this as an example where "grass is not always higher" [4]. However, there are discrepancies in the numbers within the review, and further research is needed.
4. Which Tastes Better, Grass-Fed or Grain-Fed Beef, and Why Finish Cattle on Grain?
What about taste? In one study cited in a review by Daley et al., trained evaluators preferred grain-fed beef over grass-fed beef in terms of flavor and tenderness [2].
This does not mean "grass-fed beef is bad." Differences change depending on the cattle breed, age, amount of fat, and aging method, and results vary from study to study.
The reasons for finishing with grain are explained as shortening the number of days spent raising cattle and increasing marbling (fat finely mixed into the muscle) [2]. It is said that with the same genetics and age, grain-finished cattle tend to have higher grades. However, the trend in grades is only confirmed at an overview level here.
Feeding more grain has benefits for producers. On the other hand, it puts a burden on the cow's stomach. Let us look at how Japanese farmers manage this burden.
Safety Note: It is said that with the same genetics and age, grain-finished cattle tend to have higher grading [2].
5. What Happens in a Cow's Stomach If Grain Is Increased Suddenly?
Starch from grain ferments quickly in the rumen and increases acid. If given suddenly in large amounts to cattle that are not used to it, the pH (a number indicating acidity or alkalinity) of the rumen drops, which can cause a condition called acidosis. When pH drops, the activity of microorganisms that break down fiber also decreases [2].
As a rough guide, problems are said to occur if the pH falls below 5.6. However, this value is a guideline and varies depending on the cow and the feeding method.
In the example described, farmers do not increase concentrate feed all at once. To prevent the rumen environment from changing suddenly, they increase it gradually over multiple feedings.
Microorganisms that break down grass are important workers even for grain-finished cattle. In raising cattle for marbling, farmers pay attention to the state of the rumen and increase feed gradually.
6. How Can You Compare Beef Fat Color at the Meat Counter?
If you have a chance to go to a meat counter, try comparing the color of beef fat. You only need to look; there is no need to touch it. You might see fat that is nearly white and fat that has a slight yellow tint. If the label lists the origin or raising method, record it along with the color in your notebook.
However, you cannot decide if it is "grass-fed" or "grain-fed" based on color alone. As seen in this article, color can change depending on other conditions like cattle breed and raising method. Keep observation as a starting point for questions.
If you want to investigate further, you can search for "Rice straw feeding after grazing and beef carotene and vitamin E" in NARO's research results. In nutrition labels for food at home, the numbers for the same component may differ between "per 100g" and "per serving." Comparing both shows how the impression of numbers changes with units. The original source for fatty acid comparison is the review by Nogoy et al. (Source [4]).