Thus, cattle can be labelled free-range yet not necessarily be grass-fed, and vice versa, and organic beef can be either or none. Another term adopted by the industry is grass-finished (also, 100% grass-fed), for which cattle are said to spend 100% of their lives on grass pasture. However, this label is not regulated. The Agricultural Marketing Service of the United States Department of Agriculture previously had a regulated standard for certification as "Grass Fed" meat, but withdrew the standard in 2016. However, producers must still apply the USDA's Food Safety and Inspection Service for the right to put "grass fed" on a label. Corn-fed Cattle called corn-fed, grain-fed or corn-finished are typically raised on maize, soy and other types of feed. Some corn-fed cattle are raised in concentrated animal feeding operations known as feed lots. In the United States, dairy cattle are often supplemented with grain to increase the efficiency of production and reduce the area needed to support the energy requirements of the herd. A high-energy diet increases milk output, measured in pounds or kilograms of milk per head per day. Barley-fed In Western Canada beef cattle are usually finished on a barley-based diet. Flax In some parts of the world flax (or linseed) is used to make linseed oil, and the substance is mixed with other solid cattle feed as a protein supplement. It can only be added at low percentages due to the high fat content, which is unhealthy for ruminants. One study found that feeding flax seeds may increase omega-3 content and improve marbling in the resultant beef, while another found no differences. Other supplements There are many alternative feeds and supplements which are given to cattle; these range from alfalfa and other forages, silages of diverse plants, crop residues such as pea regrowth, straw or seed hulls, residues from other production such as oilseed meal cake, molasses, whey, and crops such as beets or sorghum. Medicinal and synthetic products Cattle feed may also include various substances such as glycerol, veterinary drugs, growth hormones, feed additives or nutraceuticals to improve production efficiency. Antibiotics Antibiotics are routinely given to livestock, which account for 70% of the antibiotic use in the United States. This practice contributes to the rise of antibiotic-resistant bacteria. Antibiotic resistance is a naturally occurring phenomenon throughout the world due to the overuse and/or inappropriate use of antibiotics. The most common form of antibiotics are