Grain vs Grassfed

What is the difference between grassfed and grainfed meat?
Grassfed meat comes from animals that have only grazed on grass. They feed on a range of different types of grasses, depending on climate and region. In Australia, cattle and sheep are predominantly grassfed and account for, on average, approximately two-thirds of overall beef and sheepmeat production.
Grainfed meat comes from animals which are fed grass for most of their lives and then transition to grain-based diets for the remainder of their lives. The number of days during which they are fed a grain-based diet varies.
In Australia, grainfed animals are typically fed grain for the last 70 to 100 days of life. This type of feeding is also called grain finishing. Use of grain finishing depends on market requirements and seasonal conditions and represents, on average, a third of total production.
Grain feeding which involves 300 days or longer on grain-based diets represents a small percentage of overall production and is used to produce meat for niche markets only.

Why is grain feeding used?
Livestock are fed grain for several reasons, including to maintain a consistent meat supply, improve eating quality, meet specific needs for niche markets (e.g. for highly marbled meat), meet the energy needs of animals when pasture is limited (such as in drought conditions) and increase animal size.
What grains are used to feed animals?
Animals are fed a selection of grains not suitable for human consumption, including feed-grade wheat, barley, sorghum and triticale.
Grains are combined with lupins or field peas, by-products of cottonseed or canola, and silage or hay to deliver the necessary protein, carbohydrate, fat and roughage required to ensure nutritional requirements are met. These ingredients are different to those used in the US, where soy and corn predominate.
Is there a difference in omega-3 content between grassfed and grainfed meat?
There is no clear difference in the omega-3 content of grassfed and grainfed meat available for purchase in Australia.
The omega-3 content of meat depends on the alpha-linolenic (ALA) content of the feed. Grasses contain ALA, which ruminants convert into long-chain omega-3 fatty acids, including EPA, DPA and DHA. The amount of ALA and, consequently, the omega-3 content of meat, vary depending on the type of grass consumed. Hence, grasses with high ALA content produce meat with high omega-3 content whereas grasses with low ALA-content produce meat with comparatively lower levels of omega-3.
Grains used for feed contain low to no levels of ALA so, when animals transition to a grain-based diet, there is a decline in long-chain omega-3 levels. However, the extent of the decline will depend on the background diet, a factor which is often not considered in studies comparing grassfed with grainfed meat.
Since the ALA content of the background grass diet is highly variable, the difference between grassfed and grainfed is also variable. Hence, a grainfed animal fed a high ALA background diet may have higher levels of omega-3 than a grassfed animal fed a low ALA grass diet. For this reason, an average of random samples available for purchase in Australia provides a good estimate of the omega-3 content of meat, whether grassfed or grain finished.
Is grainfed meat more marbled than grassfed meat?
The production systems commonly adopted by Australia’s retail meat producers means there is little difference in marbling between grassfed and grainfed cattle.
Marbling refers to the fat found inside the muscle (intramuscular fat) and increases as animals get fatter, irrespective of feed type. It’s a simple equation: the longer cattle stay on a nutrient-rich diet, the fatter they become and the higher their marbling.
Since the nutritional content of grain-based feeding regimes is prescribed and food is more easily available, growth tends to be faster in grainfed than grassfed animals, so you might expect grainfed animals to have higher marbling. However as grain feeding in Australia is usually of short duration, it has little impact on marbling.
An Australian study comparing meat from grassfed and 80-day grainfed cattle found very similar total amounts of fat (as fatty acids) in the fully trimmed muscle. However, when animals were fed grain for a longer time period (150-200 days), total fat content increased.
With limited marbling, the major determinant of fat content in Australian cattle is therefore separable fat, which is found either on the outside of meat (selvedge fat) or between muscles (intermuscular fat). When trimmed of all separable fat, fat content can be as low as 2% to less than 6% for raw beef, and 3% to less than 7% for raw lamb, depending on the cut.
Is Wagyu beef high in fat?
Wagyu is a breed of cattle famous for its highly marbled meat. However, it is not so much the type of breed, but the duration and type of feed which determines the overall fat content.
Hence, meat from Wagyu beef fed for 300 or more days on a grain-based diet will be highly marbled and higher in fat compared to meat from grassfed Wagyu, which will have levels of marbling comparable to other breeds fed similar diets.
References:
Food Standards Australia and New Zealand, NUTTAB 2010 online searchable