How did US Cattle and Hogs Gain so Much Weight?

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Commercially, livestock producers benefit from ongoing breeding efforts. The wide array of livestock breeds, importance of feed quality, and the impact of drugs make it difficult to identify the primary catalyst behind rising slaughter weights. However, it seems clear that grower selection of potential mates for their female stock has a significant impact. Prices for genetic material from different bulls and boars can vary by as much as 1,400 percent, indicating that results vary as well. In the poultry industry, we see turkeys that have been bred for such an extreme size that they are physically unable to reproduce naturally.

Better feed, heftier livestock

Feed quality has improved greatly. The United States' surplus grain production combined with sophisticated software ensure that livestock receive close-to-optimal nutrition at each stage of their lives. Furthermore, the rapid growth of the fuel ethanol program since the enactment of the Renewable Fuel Standard in 2007 has produced a similarly rapid growth in the supply of distillers dried grains (DDGs). Manufacturing plants producing ethanol also produce DDGs as byproducts, and in 2016, they provided 45 million more tons of high-quality nutrition for American livestock.

Make Ethanol, Get DDGs


The expanding sizes of US hogs and chickens coincided with the rapid expansion of US soybean cultivation, from 54 million acres in 1975 to 89 million in 2015. Earlier feed rations typically skimped on expensive protein. Soybean meal contains almost 50 percent protein, and computers direct farmers to combine it with other nutrition sources, producing precise mixtures which encourage and enable quick weight gain. Time is money for livestock producers, and they work hard to generate as many pounds of meat per day as possible.

Increased Acreage Leads To Better Fed Livestock


Proper processing of ingredients also boosted feed’s total nutritional value. Various preparation methods—including rolling, grinding, steam flaking, and roasting—can increase the absorption of calories and helpful compounds by significant amounts ranging up to 14 percent in the case of popping grain sorghum. Producers now use a cost-benefit analysis to guide them in processing the feed for maximum efficiency instead of just dumping raw grain in fodder troughs. They also add flavoring to feed mixtures, which motivates livestock to eat more. Industry critics regard both processing and flavoring of feed ingredients as positive practices with no harmful consequences.

Drug and chemical usage in feed

But, some of the lucrative techniques that the producers have pioneered fail to inspire admiration. Collectively referred to as “growth promoters,” various chemicals and drugs have entered US livestock feed rations to varying effect. Broad classifications include: nutriceuticals, antibiotics, steroids, and beta-agonists. Popular movements and protests have emerged to encourage a reduction in the usage of many growth promoters, in some cases lumping helpful and harmless animal health solutions with potentially dangerous practices.

Steroid administration became a big part of US livestock agriculture shortly after German and Swiss chemists discovered the drugs in the 1930s. Producers implant slow-release steroid capsules in nursing calves and routinely see growth increases of 10 to 20 percent depending on the number and timing of implants. Feed usage declines with steroids as well, with reductions of between 2 and 5 percent commonly realized. Substantial economic benefits accrue to producers who make use of steroids.

Yet consumers are concerned about the impact of livestock steroid programs on their health. Research has shown conclusively that some meat products can retain drugs that affect human development. In 1988, the European Union banned the use of all hormone growth promoters, including steroids. US sentiment has turned against their use as well. As a result, producers who forego steroids can qualify for various premium labels and therefore charge higher prices. Steroid use is down over the past 10 years among livestock in the US, but around one third of producers still admit that they use the drugs.

Antibiotics have hugely financially beneficial effects in the livestock industry. Living organisms harbor various bacterial infections at all times at varying intensities. Supporting those (and other) parasites consumes biological resources that might otherwise go to additional growth. Prophylactic administration of antibiotics in livestock started almost immediately after the synthesis of penicillin in World War II. After many generations of antibiotics, the livestock industry now consumes close to 80 percent of the drugs by volume in the US. Through a combination of overprescription to humans and massive consumption by animals, some bacteria that can attack humans have become antibiotic resistant. Scientists have been warning about this possibility for decades, and now we see drug-resistant bacterial outbreaks on an ongoing basis. At some point, the livestock industry may face overwhelming pressure to abandon antibiotics in order to protect human health. But for now, the drugs form an important, but widely deplored, part of producers growth-promotion arsenal.

Rising Antibiotic Use in Food Animals


The addition of vitamins has helped to increase animal weights, and seems completely innocuous in terms of harmful effects. Only a century ago, people commonly died from severe vitamin deficiencies due to ignorance. Veterinary medicine lagged even further behind. Part of the software revolution in feed mixing has led to the addition of adequate amounts of various vitamins to fodder that lacks them. Avoidance of vitamin deficiency related disease and resultant healthy growth has certainly made up part of the increase in livestock weights.

In the 1980s, scientists found that a class of human asthma drugs called beta-agonists promote cattle and swine growth by about 15 to 25 percent with no extra feed use. Producers welcomed this discovery and enthusiastically added the drugs to the feed rations. The US Food and Drug Administration approved their use in 1999, claiming that the compounds break down quickly in animals’ bodies and therefore do not persist at significant levels in meat consumed by humans. Most governments around the world disagree, including the EU, Russia, China, and Taiwan. The most common veterinary beta-agonist, ractopamine, has been banned for use in livestock in over 160 countries. Trade disputes over US meat frequently feature criticism of the drugs, but the US continues to use them heavily.

One controversial beta-agonist was temporarily all-but-eliminated from US livestock feed rations. Merck Animal Health voluntarily withdrew its zilpaterol (trade name Zilmax) from the market in August 2013 after numerous complaints about lameness and other symptoms in cattle consuming the drug. After redesigning the dosage protocol, now Merck is looking for ways to reintroduce it in the US. Their trouble comes from Tyson’s and Cargill’s preemptive statements that they will never again buy Zilmax-treated cattle. That’s not as self-sacrificing as it sounds—US cattle producers have simply switched to an analogous drug, ractopamine (trade name Optaflexx).

Organic labeling does not require producers to forego beta-agonist use, because the wording of the organic standard does not exclude non-hormonal feed additives. The USDA has issued a new labeling standard which says “Ractopamine Free” for those in the US concerned about beta-agonists’ effects.


Over the past 40 years, US livestock weights have ballooned. Interestingly, in the same time period, the average man in the US gained around 25 pounds, going from 170 pounds to 195 pounds. Concerns about some of the techniques and drugs used to help the animals’ rapid weight gain have led to bans and limits on their use.

The data show some signs of a tapering in livestock weight increases, possibly due to a reduction in the volumes of steroids, antibiotics, and beta-agonists being fed to and implanted in the animals. It seems possible that a more “natural” husbandry could help to tame the world’s rapidly growing obesity problem. While much of the growth in livestock sizes can be attributed to superior feeding practices, some of it is due to abuse of veterinary pharmacology. Consumers want that to stop, but we’ll see whether they will gladly absorb the additional cost of the drug-free meat.

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