Bred to Be Sick

Unnatural growth rates can lead to crippling deformitiese

According to a textbook on avian virology, “Viral infections can move fastest through groups of birds maintained in closed, crowded, unsanitary conditions.”¹⁸¹⁰ Under such conditions, even healthy immune systems might be overwhelmed, but immune competence among modern poultry breeds may be at an all-time low. Breeding for production traits, like increased breast muscle in meat-type birds or increased egg-laying in egg breeds, seems to necessarily mean breeding for decreased immune function. Given the intensive breeding-out of immune functionality, almost all modern commercial chickens may be “physically compromised” in a way that would facilitate wild waterfowl viruses taking hold. “[D]omestic poultry have been bred to be plump and succulent rather than disease-resistant,” a senior virologist at the Australian Animal Health Laboratory points out. “[T]hey’re sitting ducks, so to speak, for their wild cousins’ viruses.”¹⁸¹¹

It wasn’t until well into the 20th century that the poultry industry began segregating chicken breeds—some for meat and others for eggs.¹⁸¹² Once maximum productivity became the emphasis, these two traits became mutually exclusive. For broilers, “meat output per chick” is considered the most important goal,¹⁸¹³ so the bigger the better.¹⁸¹⁴ In contrast, the industry wants laying hens to be small. Big eggs from small bodies ensures that more of the feed goes into the egg rather than being “wasted” on the upkeep of the rest of the animal.¹⁸¹⁵

In the egg industry, “feed conversion,” the conversion of feed into eggs, is considered the trait with the single biggest “impact on profitability.” Modern egg-laying hens are bred to be so scrawny that it’s not profitable to raise male chicks for meat. Since they can’t lay eggs, male chicks are an unwanted by-product of the industry. It makes more economic sense to kill the male chicks shortly after hatching by the hundreds of millions¹⁸¹⁶ —grinding them up alive, gassing them, or throwing them into a dumpster to suffocate or dehydrate¹⁸¹⁷ —than to waste feed on them.¹⁸¹⁸

So, in the interest of maximizing productivity, two different lines of chickens were created, one for meat and another for eggs. As one historian noted, by the end of the 1950s, the “era of the designer chicken” had arrived.¹⁸¹⁹ The results have been extraordinary. Selective breeding over time is, after all, what turned the wolf into a poodle. Ancestors to the modern-day chicken laid only about 25 eggs a year.¹⁸²⁰ Today’s laying hens produce more than ten times that number,¹⁸²¹ leading to increasing problems with uterine prolapse¹⁸²² and broken bones due to critical weakening, as skeletal calcium is mobilized to form shells for the eggs.¹⁸²³

The “essence”¹⁸²⁴ of broiler chicken production, as poultry scientists describe it, is “turning feed stuffs into meat.”¹⁸²⁵ Chicken ancestors grew to be about two pounds in four months.¹⁸²⁶ In the 1950s the industry could raise a five-pound chicken in less than three months. Due mostly to selective breeding (in addition to growth-promoting drugs), this now takes an average of 45 days.¹⁸²⁷ Broiler chickens now grow more than twice as large in less than half the time. To put the growth rate of today’s broiler chickens into perspective, the University of Arkansas Division of Agriculture reports, “If you grew as fast as a chicken, you’d weigh 349 pounds at age two.”¹⁸²⁸ In one century, as one historian relates, “the barnyard chicken was made over into a highly efficient machine for converting feed grains into cheap animal-flesh protein.”¹⁸²⁹

Interestingly, this transformation in chickens was considered such an “outstanding example of the contribution of breeding work”¹⁸³⁰ that many of the earliest poultry scientists helped form the American Breeders’ Association,¹⁸³¹ which went on to lead the human eugenics movement.¹⁸³² Leading U.S. poultry scientist and eugenics pioneer Charles B. Davenport spoke of poultry breeding efforts as akin to “race improvement”¹⁸³³ and “purification.”¹⁸³⁴ Likewise, Heinrich Himmler’s experience with chicken breeding has been noted for having shaped his views on the subject.¹⁸³⁵

The “improvement” of poultry over the last century has been deemed “quite profitable,”¹⁸³⁶ but the industry admits to the downsides. The current editor of industry trade journals WATT PoultryUSA and the Poultry Tribune wrote, “Ongoing efforts to increase breast-meat yield, for example, have created a higher propensity for musculoskeletal problems, metabolic disease, immunodeficiency, and male infertility, primarily because the extra protein going to breast muscle production comes at the expense of internal organ development.”¹⁸³⁷

Today’s broiler chickens grow so fast that they outpace their cardiovascular system’s ability to keep up, leading to forms of heart failure like Sudden Death Syndrome (also known as “flip-over syndrome”). Heart failure is an increasingly¹⁸³⁸ major¹⁸³⁹ cause of mortality among commercial flocks, even though the birds are only a few weeks old. An industry journal reports that “broilers now grow so rapidly that the heart and lungs are not developed well enough to support the remainder of the body, resulting in congestive heart failure and tremendous death losses.”¹⁸⁴⁰

Mortality rates of broilers are up to seven times that of chickens not bred for fast growth.¹⁸⁴¹ This tradeoff is accepted if the increased mortality is compensated for by an increase in meat yield or feed conversion. To maximize profits, commercial broiler producers now accept a mortality rate of 5%.¹⁸⁴²

Chickens aren’t dying just because their circulatory systems are collapsing under the strain. Chickens bred for unnaturally developed muscles (meat) have unnaturally underdeveloped immune systems. Broiler chickens selected for accelerated growth suffer from weakened immunity, which increases mortality¹⁸⁴³ by making them “more susceptible to a variety of infectious diseases.”¹⁸⁴⁴ When you breed for one characteristic, you may lose another. The modern tomato, for example, may be perfectly round and survive to market less bruised, but it also may be tough, pink, and tasteless compared to heirloom varieties. Just as purebred poodles tend to have problems with their hips, modern-day purebred chickens tend to have problems with their immune systems.

Even excluding heart failure, studies show that the highest mortality is seen in the fastest-growing chickens, and the lowest mortality in the slowest-growing chickens. Researchers conclude, “It appears that broilers with faster growth rate are under physiological and immunological stress that makes them more sensitive to infectious diseases….”¹⁸⁴⁵ This has been shown for both viral¹⁸⁴⁶ and bacterial¹⁸⁴⁷ pathogens. In one study, broilers were intentionally infected with E. coli: 40% of the fast-growing heavier birds died, compared to only 8% to 20% mortality for slower-growing breeds. The scientists commented, “These results indicate that rapid growth rate substantially reduces broiler viability.”¹⁸⁴⁸

Research with turkeys shows the same thing, despite the president of the National Turkey Federation’s claim that “[r]ealty [sic] is that in this country the poultry industry treats the health of the birds as the number one issue.”¹⁸⁴⁹ Lighter and slower-growing turkey breeds than those conventionally used have better immune performance¹⁸⁵⁰ and are hence more resistant to stress¹⁸⁵¹ and disease.¹⁸⁵² Researchers have observed that in natural outbreaks of disease like fowl cholera,¹⁸⁵³ turkeys bred for increased egg production and those selected for increased body weight had significantly higher mortality rates.¹⁸⁵⁴ Slower-growing, lighter breeds of turkeys also have greater adaptability to the stresses associated with production, such as overcrowding.¹⁸⁵⁵ USDA researchers at the University of Arkansas went so far as to suggest in a 2005 paper in Poultry Science that “fast growth in modern turkey lines” may result in stress responses “incompatible with the severe stressors that sometimes occur during commercial poultry production.”¹⁸⁵⁶

The turkey industry has so altered the natural order that the enormous breast meat mass of commercial breeds has resulted in the birds being physically incapable of mating.¹⁸⁵⁷ “One hundred percent artificial insemination,” researchers note in Livestock Production Science, “allowed for the continuation of intense selection for body weight in male lines.”¹⁸⁵⁸ Female turkeys are inseminated by tube or syringe.¹⁸⁵⁹

Selection has been so intense that commercial turkeys, like broiler chickens, can barely support their own weight. A staff editor of the leading U.S. livestock feed industry publication writes that “turkeys have been bred to grow faster and heavier but their skeletons haven’t kept pace, which causes ‘cowboy legs.’ Commonly, the turkeys have problems standing…and fall and are trampled on or seek refuge under feeders, leading to bruises and downgradings as well as culled or killed birds.”¹⁸⁶⁰ One group of researchers concluded, “We consider that birds might have been bred to grow so fast that they are on the verge of structural collapse.”¹⁸⁶¹

Many do collapse and spend much of their time lying in their own waste. Similar to broiler chickens, most turkeys in commercial production are overcrowded in warehouse-like sheds, and the majority¹⁸⁶² suffer from ulcerative contact dermatitis, from breast blisters to bed sore-like hock burns.¹⁸⁶³ These painful lesions add to the stress that may impair overall immune performance. USDA researchers conclude: “Selection of poultry for fast growth rate is often accompanied by a reduction in specific immune responses or increased disease susceptibility.”¹⁸⁶⁴

Slower growth is costly, but so are disease outbreaks. Why doesn’t the industry select for birds with improved immune responses? They’ve tried. Early in the industry’s history, rather crude methods were used to try to breed for resistance. Breeders would take baby chicks and challenge their immune systems by exposing them to adults with Marek’s disease, a poultry disease caused by a cancer-causing herpes virus. Those who lived through the exposure went on to create the next generation, one that would presumably be more resistant to the disease.¹⁸⁶⁵ No one wants to bite into a tumor at KFC.

Sometimes the chicks didn’t get infected by casual exposure, though. Breeders found that by dripping virus-laden blood from infected chickens into the eyes of baby chicks, they were able to guarantee infection, but this produced mortality rates between 30% and 60%. It was not considered economical to kill more than half the chicks. “Challenge by intraperitoneal injection of whole blood or suspensions of fresh tumorous gonads from clinically sick birds was also tested,” poultry scientists report, “but later discontinued because the mortality rates exceeded the optimum of 50%….” The intent was to kill off half the chicks, but injecting ground-up tumorous sex organs into the abdomens of baby chicks turned out to be a little too fatal.¹⁸⁶⁶

Challenge tests continue in poultry breeding,¹⁸⁶⁷ but on a much smaller scale. This kind of direct selection is considered “inconvenient” in intensive production systems due to the costs involved.¹⁸⁶⁸ Breeders have tried selecting for antibody response directly, but poultry scientists have found that those with the best antibody responses consistently had significantly lower weights at all ages.¹⁸⁶⁹ Research dating back 30 years shows that chickens bred to be disease-resistant have lower body weight and produce smaller eggs.¹⁸⁷⁰ Studies suggest that immune defects may actually enhance poultry performance.¹⁸⁷¹ Seems like you can have one or the other, immunity or growth. And the industry chooses growth.

This happens across species. Growth and disease susceptibility have been shown to go hand-in-hand in pigs,¹⁸⁷² cattle,¹⁸⁷³ and dairy cows. Over the past century, genetic manipulation of dairy cows through selective breeding has tripled the annual milk yield to 18,000 pounds of milk per cow. It took the first half of the century to force the first ton increase, but since the 1980s, the industry has managed to add extra tons every eight or nine years.¹⁸⁷⁴ Turning cows into milk factories has taken a toll on their immune systems,¹⁸⁷⁵ increasing their risk of mastitis,¹⁸⁷⁶ infections of the udder. Mastitis may be painful for the animal and spike the milk supply with increasing levels of somatic (pus) cells, but decreased cow immunity, as opposed to decreased chicken immunity, is unlikely to aid and abet in the killing of millions of people.

Why is immunity reduced when production is maximized? Our best understanding is the “resource allocation theory.” There is only a certain amount of energy, protein, and other nutrients coming into an animal’s system at any one time. Those resources can go to build muscle or to host defense, like a national budget in which money is divided between the country’s infrastructure and homeland security. So dairy cows, for example, have been bred to “redirect resources from the maintenance of an adequate immune system to milk production in order to maintain advantages in milk yield,” reads one dairy science textbook.¹⁸⁷⁷ This is a trade-off between production traits and immunocompetence.¹⁸⁷⁸

Studies show that old-fashioned, slower-growing chicken breeds have larger¹⁸⁷⁹ and better developed¹⁸⁸⁰ antibody-producing immune organs. Instead of being bred to transfer the bulk of resources to build breast meat while neglecting other needs, these slower-growing breeds had sufficient resources to foster a more functional antibody response system.¹⁸⁸¹ Antibodies are critically important for vaccine effectiveness, particularly in animals like broiler chickens who are killed after only a handful of weeks of life and don’t have time to acquire a set of their own immune memories. “Those animals which are intensively reared and slaughtered young,” notes one agricultural microbiologist, “will have the greatest potential for carrying pathogens.”¹⁸⁸²

One of the reasons that 1% to 4% of broilers die from “acute death syndrome”¹⁸⁸³ (in which chickens suddenly lose their balance, violently flap their wings, go into spasms, and die of acute heart failure) is that the metabolic demand for oxygen created by the increasing muscle mass leaves the rest of their body short of oxygen.¹⁸⁸⁴ Forget immunity—many modern broiler chickens can hardly keep up with breathing. Meat-type birds outgrow their lungs, hearts, and immune systems.

The maintenance of an effective immune system is metabolically very costly.¹⁸⁸⁵ The “big eater” macrophage immune cells burn through almost as much energy as maximally functioning heart muscle.¹⁸⁸⁶ Antibodies are made out of protein. When the body is churning out thousands of antibodies per second, there is less protein available for growth. Studies show that chickens capable of mounting a decent antibody response have lower weight and lower weight gain than chickens with suboptimal antibody production.¹⁸⁸⁷

Germ-free chicks raised in germ-free environments grow faster than chickens in unsanitary environments.¹⁸⁸⁸ Even minute exposures to the normal microbial flora of the gut are enough of an immune stimulus to significantly reduce growth rates.¹⁸⁸⁹ Though there’s no tissue damage and no evidence of disease, just the normal day-to-day functioning of the immune system diverts energy from maximal growth.¹⁸⁹⁰ That’s why you can feed germ-free chickens in a sanitary laboratory environment all the antibiotics you want and there will be no change in growth rates, whereas commercially confined chickens fed antibiotics demonstrate a remarkable spurt in growth.¹⁸⁹¹ By breeding for maximum production, the industry seems to be breeding for minimum immunity.

The reason that selecting for growth impairs immunity is the same reason that human AIDS and tuberculosis patients waste away. Fighting off infection requires a remarkable demand for energy and nutrients. The body shifts resources away from nonessential anabolic (meaning growth, as in “anabolic steroids”) and maintenance processes toward bolstering life-or-death defenses.¹⁸⁹² This redistribution of resources makes sense from an evolutionary point of view. What use is long-term growth when short-term survival is threatened? Not only are the body’s construction projects halted, but they start to be torn down for raw materials. People with severe infections can lose up to one-third of their body weight as the body starts eating away at itself to feed more fuel into the immune machine.¹⁸⁹³

Even relatively insignificant challenges to the immune system can significantly affect growth. Simple vaccinations can result in a greater than 20% decline in daily weight gain for farm animals and increase protein demands as much as 30%,¹⁸⁹⁴ demonstrating the perverse balance between growth and immunity. The poultry industry can’t have it both ways.

Before domestication, natural selection chose strong immune systems for survival.¹⁸⁹⁵ After domestication, though, “[a]rtificial selection concentrated on improvement of production traits with little attention to resistance to disease,”¹⁸⁹⁶ reads one poultry breeding textbook. The industry seems more interested in the survival of the fattest, not the fittest.¹⁸⁹⁷

Animals are preprogrammed by evolution to grow at the near optimal rate. The faster a juvenile animal grows to maturity in the wild, the faster he or she would presumably be able to win out over competing suitors to mate and produce more offspring. This would tend to select for maximum growth rates, but resource allocation is not the only reason Mother Nature puts on the brakes. Even in a germ-free environment, cells cannot divide and grow while simultaneously performing at peak efficiency.

Faster-growing fish, for example, swim less efficiently than slower-growing fish.¹⁸⁹⁸ Faster-growing rainbow trout have been shown to have significantly impaired swimming performance.¹⁸⁹⁹ The critical swimming speed of salmon genetically engineered to grow more than twice as fast by length as control fish is only half the speed of control fish.¹⁹⁰⁰ Not only do broiler chickens bred for accelerated growth have smaller immune organs, but what little immunity they do have may not be functioning effectively.

The budgetary analogy, therefore, is imperfect. It’s not that there’s just a certain amount of resources to go around and every dollar spent on infrastructure is a dollar not spent on defense. It’s worse than that. By forcing broiler chickens to divert the lion’s share of resources to fast growth, not only is host security left to hold bake sales, but immune defenses may be actively undermined.

The industry has tried to shore up the imposed deficiencies with feed restriction programs, improved sanitation, and chemoprophylactic treatments.¹⁹⁰¹ USDA researchers note in a 2005 Poultry Science article: “Much of the progress seen in intensive poultry production over the past 50 yr has been possible due to the availability of very effective and inexpensive antibiotics which have prevented stress-induced opportunistic bacterial disease and allowed efficient production even as density and growth rate increased.” The researchers go on to show displeasure that human health concerns are pressuring the industry away from such crutches.¹⁹⁰²

Despite drugs and new vaccines, the head of the prestigious Wageningen University Animal Production Systems group reached the sobering conclusion long ago that a modern broiler chicken “still cannot cope adequately with its pathogenic environment.”¹⁹⁰³ There is only so far we may be able to subordinate chicken biology to the dictates of industrial production before running into unintended consequences.¹⁹⁰⁴ “We are severely changing the way these animals grow,” remarked one poultry geneticist in “High Yielding Broiler Production: The Big Trade-Off,” an article in Broiler Industry. “I believe the time is rapidly approaching when management alone won’t be able to overcome the genetic problems because of the metabolic stresses that are being put on these birds.”¹⁹⁰⁵ Or, as Rachel Carson put it 40 years ago, “Nature fights back.”¹⁹⁰⁶

The history of industrial agriculture in general is replete with technological fixes associated with unforeseen consequences, such as DDT. An academic history of the broiler industry views intensive poultry production as paradigmatic in this regard. The author writes:

…virtually every effort to further industrialize broiler biology has resulted in the emergence of new risks and vulnerabilities. Intensive confinement combined with increased genetic uniformity has created new opportunities for the spread of pathogens. Increased breast-meat yield has come at the expense of increased immunodeficiency. And, of course, widespread recourse to antibiotics has created a niche for the proliferation of resistant bacteria.¹⁹⁰⁷

In an industry whose bottom line is the bottom line, though, it all makes good business sense.

The poultry industry accepts the fact that broilers with the fastest growth rates start suffering from heart failure as they reach slaughter-weight and may just keel over dead, even after they have “already consumed almost all of their feed allowance and therefore taking the largest possible slice out of the profit.”¹⁹⁰⁸ But not only is that readily factored into the equation, it may be welcomed as a sign of good breeding. As one chicken farmer wrote, “Aside from the stupendous rate of growth…the sign of a good meat flock is the number of birds dying from heart attacks.”¹⁹⁰⁹

An interesting proviso is added by leading poultry breeding expert Gerard Albers. Although “decisions in the poultry industry are largely and increasingly driven by economic considerations,” Albers notes, “the psychological impact of flock morbidity and mortality on the farmer cannot be ignored. Mortality rates above a certain psychological threshold are unacceptable.” The excess mortality may just become too disturbing. Albers is not optimistic, though, that breeding for “increased livability” will take precedence over selection for “more profitable” traits.¹⁹¹⁰

The same attitude pervades the egg industry. In an article titled, “Industrial Perspective on Problems and Issues Associated with Poultry Breeding,” laying hen breeding corporations insist that “[e]gg production per hen housed will continue to be the single most important trait under selection.”¹⁹¹¹

In the broiler chicken industry, the costs of production diseases are estimated at 10% to 20% of total production costs,¹⁹¹² a small price to pay for jumbo-sized birds. It is simply not in the financial interest of the industry to fully mitigate disease rates. As poultry researchers have asked, “Is it more profitable to grow the biggest bird and have increased mortality due to heart attacks, ascites [heart failure], and leg problems, or should birds be grown slower so that birds are smaller, but have fewer heart, lung, and skeletal problems?” Their answer: “A large portion of growers’ pay is based on the pound of saleable meat produced, so simple calculations suggest that it is better to get the weight and ignore the mortality.”¹⁹¹³ In the face of bird flu viruses like H5N1, though, the deaths of chickens aren’t the only mortalities the industry may be ignoring.

The industry could breed for improved immunity even though it has “been shown to result in decreased body weight,”¹⁹¹⁴ but openly admits that “disease resistance will not be selected for if the cost in a loss of genetic improvements in other traits is too great.” The industry prefers to externalize, or pass along, disease costs to the human population. “For example,” an industry breeding text reads, “to select for effective resistance to Salmonella would currently cost so much in performance that it would be totally unfeasible.”¹⁹¹⁵ It doesn’t seem to matter that Salmonella rates in poultry continue to rise in the United States,¹⁹¹⁶ nor that hundreds of Americans die from Salmonella every year.¹⁹¹⁷ Let the consumers sterilize their meat thermometers and be extra careful not to drip a drop of fecal fluid on their kitchen floor so as not to endanger their toddlers.

Europe is reconsidering its breeding program. The European Commission’s Scientific Committee broiler chcken report stated that its “most important recommendation” was that “[b]reeders should give a considerably higher priority to health variables in the breeding index, if necessary at the expense of the selection pressure for growth and feed conversion.”¹⁹¹⁸ Meanwhile in the United States, growth rates continue to be pushed faster every year.¹⁹¹⁹ One poultry specialist mused, “Mathematically, it is evident that the present rate of improvement in growth cannot be continued for more than a couple of decades, or the industry will be faced with a bird that virtually explodes upon hatching.