Genetics and Animal Welfare


Department of Animal Science
Colorado State University
Fort Collins, Colorado

Genetics and the Behaviour of Domestic Animals, T. Grandin (Editor), Academic Press, San Diego, California, pp 319-341(1998), with 1999 updates.


The productivity of domestic livestock and poultry has almost tripled in the last 100 years through the use of both improved feeding methods and genetic selection. Freeman and Lindberg (1993) stated that improvements in genetic selection in the dairy industry have contributed more to increased milk production than improvements in management. Furthermore, the National Milk Producers Federation (1996) reports that during a 30-year period milk production in Holstein cows more than doubled. Similar gains have been made in poultry (Gordy, 1974; Maudlin, 1995). Due to genetic selection, the ability of a chicken to gain weight has increased phenomenally In 1923 it took 16 weeks to produce a broiler chicken. In 1993, only 6 1/2 weeks were required. Both authors are concerned that in the future, the most serious animal welfare problems may be caused by overselection for production traits such as rapid growth, leanness, and high milk yield.

Several long-term selection studies using a variety of small animals have clearly shown that overselection for a single trait may have adverse or unexpected effects on other traits (Lerner, 1954; Dobzhansky, 1970; Wright, 1978; Belyaev, 1979). Belyaev (1979) and Belyaev and Borodin (1982) demonstrated the effects of overselection for a single trait in long-term selection experiments in foxes. Selecting foxes for a single behavioral trait (tameness) caused unexpected changes in coat color, breeding cycles, hormonal profiles, and subsequent changes in body traits.

In domestic pigs, selection for meat production traits has resulted in animals with lowered reproductive ability (Dickerson, 1973). To compensate, modern pork producers often use maternal sow lines which have been selected for high reproduction ability. They are bred to sire lines selected for high meat production. The resulting offspring are terminal cross animals that are fattened for market. Buchanan (1987) stated that the use of crossbreeding in the swine industry has increased in the last 60 years. In the 1990s, nearly all commercial market pigs are crossbred.


Since 1971, the first author has observed hundreds of thousands of animals at slaughter plants, farms, and feedlots in the United States, Canada, Europe, Australia, and New Zealand. In the early 1990s she started to observe an increased number of highly excitable, nervous pigs and cattle. These animals are more difficult to handle and they are more likely to panic and become extremely agitated when subjected to sudden novel experiences. For example, a light tap on the rear causes squealing in pigs with an excitable temperament, but it has little effect on pigs with a calmer temperament. The appearance of highly excitable and difficult to handle animals appeared to coincide with genetic selection for both rapid growth and high, lean meat yield (Grandin, 1994). The most highly excitable and reactive cattle are primarily crossbreds of breeds from the European continent. In the United States, these cattle became popular when producers started selecting for lean beef (Grandin, 1994). Stress caused by fearful and panicked animals increases meat quality problems. Excitable cattle that become highly agitated during handling are also more likely to have tough meat and more dark cutters (Voisinet et al., 1997). Pigs that become excited shortly prior to slaughter have more PSE and lower meat quality (Sayre et al., 1964; Barton-Gade, 1984).

In both the United States and Australia, cattle are grain fed in large outdoor feedlot pens. In the 1970s, the first author never observed tongue rolling or other abnormal behaviors in grainfed cattle. However, in 1996 she visited several feedlots which fed thousands of Hoisteins and observed "stereotypic" (abnormal) tongue rolling. Some Holstein steers excessively licked every surface in the feedlot pen, such as fences and gates. They did this even though they were fed ad libitum grain and corn. Licking was so excessive that they learned to lick open gate latches that the beef breeds had never opened. None of the beef breed cattle in these same feedlots engaged in constant licking or tongue rolling.

Both authors speculate that continuous selection for high milk production may explain the great increase in licking. In order for a Holstein cow to produce a large amount of milk, she has to eat a large amount of food. Selection for milk production also requires selection for increased feed intake. We further hypothesize that licking fences and gates might be a precursor to more serious problems if genetic selection for the highest production is continued. The increased incidence of "weaver" condition in Holsteins is possibly related to increased selection for high milk production. Weaver is an inherited degenerative mycloencephalopathy (Freeman and Lindberg, 1993).

From a behavioral standpoint, the welfare of grainfed Holstein steers is probably not compromised, but from a health standpoint there are already problems. The first author has observed that Holstein steers on a high grain ration have more bloat than beef breeds on similar rations. In addition to bloat, grainfed Holsteins have more sudden death than beef cattle. Sometimes normal, healthy-appearing Holsteins died suddenly while standing at the feed trough.

Beef breed cattle that die in a pen usually move away from the feed trough when they get sick. Hoisteins bred during the mid-1990s can be succesfully managed, but if breeders continue down the genetic road they are now on, there might be serious welfare problems.


The welfare of poultry has already been compromised by genetic selection for rapid growth and high meat production. Muscle mass in broiler chickens has been selected to grow very quickly, but growth of the skeleton and the internal organs has not kept up. Broiler chickens have reduced cardiopulmonary capacity in relation to their muscle mass, and cannot withstand much physical exertion (Broom, 1987, 1993a; Julian, 1993; Julian et al., 1986).

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The author has observed that breeders have bred brooiler chickens to have stronger legs. However an unexpected problem has arisen. Heavy muscled broiler hybrids with strong legs have overly aggressive roosters that may injure the hens during breeding. Ian Duncan, University of Guelph, speculates that this problem is caused by deletion of the rooster's normal courtship pattern. Traits are linked in unexpected ways.

Reproductive efficiency is also reduced by extensive selection for muscle growth. For example, extensive muscle growth can make mating difficult, or may reduce fertility. Turkeys selected for large breasts are unable to breed naturally (Dinnington et al., 1990). Another example is Belgium Blue cattle that are so heavily muscled that they must have a high percentage of their calves by cesarian section (Broom, 1987,1993).

Welfare problems caused by genetic selection have also occurred in pigs. Some pork producers deliberately use boars that are positive for the PSS (Porcine Stress Syndrome) gene. The crossbred offspring from these boars have a higher percentage of lean meat and larger loin eyes (Aalhus et al., 1991). PSS is inherited in a classical Mendalian manner. Pigs which are either homozygous negative or heterozygous with one PSS gene (carrier state) will not display the symptoms of PSS when they become excited. Pigs which contain a PSS gene from both the sire and the dam (homozygous positive) will often have a heart attack and die when they become excited. When a homozygous positive PSS boar is bred to a sow which is free of the PSS gene, none of the offspring will be homozygous positive for PSS. To maximize kilograms of lean meat, swine breeding companies sell PSS homozygous positive boars for breeding to PSS homozygous negative sows. A welfare problem is created if a producer breeds PSS heterozygous sows (carrier state) to a PSS homozygous boar. Unfortunately this practice is quite common because a producer can breed terminal cross guts from his own herd instead of buying new gilts which are homozygous negative and completely free of the PSS gene.

The first author has observed that compared to older genetic lines of pigs with more back fat, some of the lean hybrid pig lines developed in the 1990s often have five times as many death losses. Truck drivers who transport pigs have reported that they often have one or two dead pigs on a truckload of hybrid market animals. These deaths may occur even if the pigs are transported under good conditions. Older genetic lines often have no dead pigs on a truck. Many of the truck loads with high death losses contain pigs sired by PSS positive boars. Published studies on death losses indicate that pigs with Pictrain genetics have almost double the death losses. Broom (1993b) reports that death loss in the Netherlands for Pictrain X Landrace pigs is 0.7%. Surveys conducted on the older fatter type pigs had death losses ranging from 0.1 to 0.4% (Hails, 1978; Holloway, 1980; Grandin, 1981; Lambooij et al., 1985). Problems with high death losses in ultralean hybreds is a more serious problem in the United States than in Europe. Death losses in Europe are much lower for the same hybrid pig lines from the same commercial breeding company The reason for this may be that pigs reared for slaughter in Europe are fed a limited grain ration and are grown more slowly. Slower growth results in market weight pigs that are older and more mature. In the United States, market pigs are fed ad libitum grain and attain market weight at an earlier age. Another factor which may increase death losses in the United States is higher slaughter weights compared to pigs in Europe. The first author has observed that heavier animals are more likely to die during transport or collapse during physical exertion.

Use of the PSS gene provides a high quantity of lean pork at the expense of quality. Fortunately, the pork industry may reduce the use of this gene because pigs that carry the gene have poorer meat quality (Serge and Houde, 1993). Even though heterozygote pigs which carry one PSS gene do not express PSS symptoms, their meat production traits are intermediate in both quality and quantity between PSS homozygous positive animals and pigs which are free of the PSS gene. Many leaders in the U.S. pork industry agree that the PSS gene should not be used in the production of pork (Miller, 1996). The stress gene became popular because some slaughter plants in the United States pay pork producers on the basis of the quantity of lean pork instead of quality. A U.S. survey on pork quality in 1991 indicated that PSE (Pale Soft exudative) pork levels were 16% (Kauffman et al., 1992). In contrast, PSE levels are under 5% in Denmark (Barton-Gade, 1984). Danish producers have worked to eliminate the PSS gene from their herds because they export high-quality pork.

Elimination of the PSS gene is not going to solve all of the welfare problems which may be associated with breeding pigs for extreme leanness or rapid muscle growth. Even if the PSS gene is eliminated, it is likely that indiscriminant selection for extreme production traits may still cause problems with death losses due to insufficient cardiac capacity or excitability and nervousness. Pigs that are free of the PSS gene can still yield poor quality pork if they become excited at the slaughter plant.


Animals genetically selected for rapid weight gain or production of large quantities of milk, eggs, or meat require a tremendous appetite and food intake in order to generate large amounts of these products. Selection for rapid increases in muscle mass is highly correlated with selection for increased appetite drive. Research on chickens shows that birds selected for egg production stop eating when their metabolic needs are met, but broiler chicken selected for meat production do not stop eating until their gut is completely full (Nir et al., 1978).

The welfare of broiler chickens and market pigs being fattened for slaughter is quite good because they are allowed to eat until satiated. However, a welfare problem may occur in breeder hens and sows that produce the fast-gaining offspring because they have to be maintained on a calorie restricted diet (Close, 1996). Broiler breeders on a restricted diet produce more eggs (Robinson et al., 1991), but if they are allowed to eat until satiated, they develop reproductive problems (Yu et al., 1992a). Furthermore, if sows are fed all they can eat they become overfat, which can result in leg problems and difficulties farrowing. The problem is that the animal's appetite far exceeds its basic metabolic needs.

To prevent broiler breeder chickens used for egg production from becoming overweight, they are fed 60 to 80% less than they would eat if fed ad lib (Karunajeewa, 1987; Yu et al., 1992a,b; Hocking, 1993; Hocking et al., 1993; Zuidhoff et al., 1995). Even when the hens go into egg production to produce broiler chicks, they are still restricted to 25 to 50% of what they would eat if they ate until satisfied. Feed restriction in sows is slightly less extreme compared to broiler chickens. Gestating sows are fed approximately 60% of their ad lib intake of a standard grain concentrate diet (Lawrence et al., 1988). A sow nursing piglets is allowed to eat all she wants, but during gestation she is kept on a calorie restricted diet to prevent her from becoming too fat.

A review of a number of studies shows that feed restriction in breeding sows and chickens results in many abnormal behaviors such as stereotypies (Lawrence and Terlouw; 1993). Appleby and Lawrence (1987) found that stereotypies developed in sows only when their feed intake was restricted. In a subsequent experiment, the same research team concluded that the amount of feed that sows are fed on commercial farms is not high enough to satisfy their motivation for feeding (Lawrence et al., 1988). They further concluded that hunger resulting from a restricted diet may be a major cause of stress in confined housing systems. Bergeron and Gonyou (1997) found that stereotypies developed when the diet did not have sufficient energy to prevent hunger. Similar results have been found in other animals. Savory et al. (1992) found that feed restriction in broiler breeder hens results in stereotypies.


It is a common practice in the poultry and pork industry to feed highly concentrated diets consisting of mostly grain to breeding sows and broiler breeders. This does not compromise the welfare of market animals that are fed ad lib but it may increase welfare problems in calorie restricted breeding animals. Studies in poultry, pigs, and cattle show that the incidence of abnormal behavior can be reduced by providing roughage in the diet (Zuidhoff et al., 1995; Lawrence et al., 1989; Robert et al., 1993; Redbo and Nordblad, 1997). Roughage helps to reduce stereotypies and other abnormal behavior because diets high in roughage can be restricted in calories and fill the animal's gut. Diets with added roughage also take more time to eat and satisfy the animal's motivation for mouth activities. However, artificially increasing food intake time by placing hanging chains in the feed trough failed to reduce the development of stereotypies (Bergeron and Gonyou, 1997).The wild ancestors of chicken and pigs spent many hours pecking and rooting to obtain their food. Stolba and Wood-Gush (1989) report that domestic swine reared in woods and grasslands display most of the same behaviors as their ancestor, the European wild boar. Behaviors used for obtaining food such as grazing and rooting occupied large portions of each day Even though the adult domestic sows used in this study came out of an intensive housing system they quickly reverted to ancestral foraging patterns.

It is important to provide pigs with roughage which provides both gut fill and mouth activities. Feeding roughage such as straw, sugar beet pulp or oat hulls can improve the welfare of breeding animals which must be kept on a calorie restricted diet (Close et al., 1985). Zuidhoff et al. (1995) found that feeding concentrates diluted with 15% oat hulls increased the time required to consume the feed and reduced stress. Stress was measured with a heterophil/lymphocyte test. Dietary bulk alone is not sufficient to reduce feeding motivation (Lawrence et al., 1989). Chopped straw was added to the ration and hunger was measured by counting how many times boars would press a panel to obtain feed rewards. Whole straw provided to pigs is more effective for reducing abnormal behavior than chopped straw. Stereotypies in sows housed in individual stalls can be prevented by feeding small amounts of straw (Fraser, 1975). Pelleting or wafering of roughage feeds decreases bulking compared to baled hay by about 75% (Haenlein et al., 1966). Horses fed pellet diets spent more time chewing wood and eating manure compared to horses fed hay (Willard et al., 1977).

Modifying the diet by providing roughage which satisfies the motivation to manipulate and provide gut fill will improve welfare of breeding animals that have been genetically selected to gain large amounts of weight in a short period of time. However, some sectors of the industry have been reluctant to feed roughage because roughages are too bulky to move through some types of automated feeding systems. They are also more expensive to transport. Adding roughage to the diet can improve productivity. Broiler breeder hens fed a bulky diet of 15% oat hulls had higher egg production than hens fed grain concentrates (Zuidhoff et al., 1995). In Utah, swine producers reported that feeding locally grown alfalfa cubes to sows housed in stalls was beneficial. In many parts of the United States locally grown roughage are available. Feed trials at four different research stations have shown that feeding roughage will increase the number of piglets born.

While feeding roughage can reduce hunger motivation in some highly productive breeding animals, it may not always be sufficient to maintain welfare. Tina Widowski, an animal welfare specialist at the University of Guelph in Canada, has extensive experience raising both breeding sows and broiler breeder chickens. She told the first author that "broiler breeders are so highly selected for appetite that they do not work behaviorally as animals." There is also some evidence that high-producing sows which produce large litters have more stereotypic behavior (von Borell and Hurnick, 1990).

There is a point at which there should be a limit on breeding and selecting animals for increased muscle mass, egg, or milk production. The authors fear that animals may become so highly selected for a huge appetite that their welfare may remain poor even when they are housed and fed under ideal conditions. It is likely that indiscriminant selection for increased appetite may result in grave animal welfare problems for breeding animals.


When animal welfare is being discussed, the general public is often most concerned about movement restriction. For example, egg-laying hens are housed in cages, veal calves live in crates, and gestating cows are kept in stalls where they are unable to turn around. Research clearly shows that animals are motivated for movement (McFarlane et at., 1988; Dellmeier et at., 1985); however, movement restriction may be less stressful to the animals than feed restriction (Rushen, 1993; Rushen et at., 1993). This would be especially true in animals genetically selected for high appetite. This does not mean that movement restriction is not important. In one experiment, gilts were housed in crates which made turning around difficult. In the first treatment, food and water were positioned at opposite ends of the crates so the gilts had to turn around in order to eat and drink. In the second treatment, the water and feeder were placed at the same end of the crate. Gilts that did not have to turn around did so just as many times as gilts that had to turn in order to eat or drink (McFarlane et at., 1988).

In another experiment Dellmeier et al. (1985) found that veal calves housed singly in small stalls for 6.5 weeks responded with greater activity when they were tested in an open field arena, compared to calves housed in groups in a yard. The calves housed in small stalls ran around and kicked up their heels when they were turned loose in the test arena. Calved raised in large group pens did not do this. Due to the fact that the open field was more novel for the calves housed in stalls, Pasille et at. (1995) questioned the results of Dellmeier et at. (1985). They stated that Dellmeier et al. (1985) had not controlled for the novelty factor in the test arena. The first author has observed that cattle kept in a large open feedlot pen and cattle housed singly in small "dog run" pens behave differently when they are released. Large fat cattle raised in small "dog runs" ran up and down a 3.5-meter-wide alley when they were released. The increased activity cannot be explained by the effects of novelty. Both groups of cattle were raised outside on the same farm and the alley was visible from their pens. Our informal observations support the findings of Dellmeier et at. (1985).


The literature is full of examples of dogs, pigeons, mice, rabbits, and rats which have neurological or behavioral abnormalities. In most cases, the abnormalities occurred as spontaneous mutations in laboratory stocks, which were then continuously selected for research purposes. A recent example of spontaneous mutation is muscular hypertrophy in Dorset sheep (Cockett et at., 1996). One of the most well-researched examples is nervous pointer-breed dogs. Pointers are dogs selected to freeze and point when they see game birds hidden in the bushes. Pointing behavior is similar to an orienting response that becomes frozen. The selection of pointers for the pointing trait may be selection for an abnormal orienting response. Breeders have known for years that some dogs are so nervous that they are useless as hunting dogs (Dykman et al., 1979). The pointing trait and nervousness may be linked. A neurologically normal dog will orient toward a bird or other prey then either chase it or return to its original activity. It does not stay frozen in an orienting posture. Breeders of pointers have found that there is a fine line that divides a good pointer from a bad one. Dogs with a heightened pointing response are generally too nervous to make reliable hunting dogs. Dykman et al. (1979) and Peters et al. (1967) stated that there were obvious differences in the behavior of normal versus nervous pointers. Laboratory visitors could easily differentiate which dogs were from the nervous genetic line. The genetically nervous pointers would cower in their cage and failed to approach visitors, whereas the normal pointers approached and wagged their tails.

Geneticists have selectively bred both normal pointers, with the characteristic pointing behavior, and abnormal, nervous pointers. Nervous pointers are excessively timid, and have a hyperstartle response, avoidance of people, and catatonic freezing in close presence of people (Klien et al., 1988). Some nervous pointers display strikingly bizarre behavior. One dog became "frozen" in a point and fell over when accidently bumped by another dog (McBryde and Murphee, 1974). It appears that with nervous pointers, a continuum of neurological defects exists. Further research by Klien et al. (1988) revealed that many nervous pointers were also deaf. Inherited deafness in lines of pointers selected for excessive nervous behavior is an autosomol recessive trait and the nervous trait may be inherited dominantly (Steinberg et at., 1994).

The welfare of normal pointers (ones without the nervous trait) is acceptable. However, nervous pointers may have very poor welfare unless they are raised under very specialized conditions. For example, training and environmental modification can help nervous pointers act more like normal dogs. McBryde and Murphee (1974) found that training nervous pointers alongside normal pointers made them less timid. The dogs from the nervous genetic line become less timid and followed a normal pointer. After a period of training, the nervous dogs no longer needed to be kept with a normal dog. McBryde and Murphee (1974) concluded that breeding an animal continuously for a certain genetic trait often resulted in the occurrence of other less desirable traits.

Many examples of neurological defects in animals can be found in the genetics literature. For example, roller-tumbler pigeons are bred to roll in flight. Pigeon fanciers select for birds with an intermediate expression of this trait. Birds with an excessive expression of this trait continue rolling in flight until they crash into the ground (Entrikin and Erway 1972). Pigeons that roll in flight have acceptable welfare, but when they hit the ground welfare is severely compromised. In comparison to pointer dogs, a slightly abnormal orienting response makes a good bird dog, but an excessive amount of the trait results in a dog that is a nervous wreck.


For hundreds of years the Japanese have bred "fancy" mice as a hobby. In Eu- rope, there is also long tradition of mouse fanciers (Morse, 1978). Some fancy mice were selected for abnormalities of movement. Most of the fancy mouse mutations can be found in today's laboratory mice. One is called the "Japanese Waltzer." Cools (1972a,b) reported that these animals have an abnormality of the inner ear They are also hyperactive and behave like mice injected with amphetamines (Cools, 1972a,b).

Researchers in behavior have bred rodents with many abnormalities (Seyfried 1982; Wimmer and Wimmer, 1985; Serikawa and Yamada, 1986). There is a wide variety of seizure-prone rats. Some animals have epileptic seizures triggered either by lowering their body temperature or by sound. Mutant, seizure-prone rats are so sensitive that a minor disturbance such as changing drinking bottles can cause convulsions (Serikawa and Yamada, 1986). Others are generally seizure prone and many different types of stimuli can trigger a seizure. There are also strains of rodents with juvenile onset or adult onset of susceptability to seizure. Rabbits have also been selectively bred for susceptability to sound induced seizures (Hohenboken and Nellhaus, 1970).

Genetic selection is also used to select for abnormalities such as a preference for alcohol (Wimmer and Wimmer, 1985). McCleam and Rogers (1961) discovered a preference for alcohol over water in an inbred mouse line. Crabbe (1983) found two distinct genetic effects and two separate behavioral effects of alcohol. The first effect of alcohol on mice is on activity levels after a dose. The second is "hypothermic sensitivity" which includes a long sleep time after a dose of alcohol.

Welfare problems can appear unexpectedly in rodents and small mammals used for research. The managers of a laboratory in Germany reported an increasing number of cases of extensive self-mutilation in a colony of checkered cross rabbits (Iglauer et al., 1994). The rabbits bit off their toes. The outbreak of selfmutilation occurred in rabbits that were bred for a high resistance to infection. The researchers had achieved the goal of increased disease resistance but the price was rabbits that engaged in self-injury This experience in the rabbit colony is just one more example of different ways that behavioral and physiological traits are linked. The reader must not jump to the conclusion that selecting for disease resistance will always result in abnormal behavior in all species.

The conclusion the reader should make is that when one selects for one trait many other traits will be affected. It is often difficult to predict which traits will be changed.


For centuries, animal breeders have recognized that a lack of eye and body pigmentation may signal neurological defects. Animals with extensive depigmented areas on the body are more likely to have developmental or nervous system abnormalities (Searle, 1968; Cowling et al., 1994). In animals highly selected for production traits, the degree of depigmentation could possibly serve as an early waming system for nervous system abnormalities, which cause welfare problems.

It is important, however, to differentiate between depigmentation and white animals that are fully pigmented. Arab horses and Brahman cattle have light hair and dark skin. These animals are not depigmented. The Holstein cow is depigmented in the areas of its body that are white. Depigmented areas of the body are characterized by both white hair and white skin. Light-colored cattle such as the Charolais are not depigmented because the animals have brown eyes and some hair pigment. Most beef breeds have much more pigmentation. Some crossbred white pigs with Duroc genes will have white hairs with a very faint reddish tint. The Yorkshire and Landrace pig breeds have dark-colored eyes and white hair and skin.

There appears to be a common genetic mechanism in many different mammals which determines coat color and patterns (Murray 1988). Many domestic animals have a white blaze on the forehead and a white tail tip. Dogs, cats, and cattle can all have this pattern. Schaible (1969) and Schaible and Brumbaugh (1976) explain that migration of pigment-producing cells occurs during embryonic growth, and common patterns between species frequently occur. For example, mice can be selected for a white belt on a mostly black body This pattern is very similar in appearance to that of Hampshire pigs and Belted Galloway cattle. The common white areas in all three species are characterized by a lack of pigment, both in the hair and in the skin beneath the hair. In domestic horses, depigmented facial and leg markings were not present, or were very rare in their wild ancestors (Guerts, 1977). Woolf (1990, 1991, 1995) assumes the reason for this is that white markings on the face or legs provided less color protection from predators. However, flashy white markings are favored by some breeders, and Forbis (1976) reports that common white markings in the Arabian have been present since ancient times.

Attractive white markings on the legs and forehead of horses are often deliberately selected for. In contrast, depigmentation in production livestock and poultry is possibly a secondary effect of selection for production traits. Many domestic animals are partially depigmented, especially high producing ones. A totally depigmented animal is albino with pink eyes. A good example is white rats and mice. Several food-producing animals are considered partially depigmented and have either colored eyes or some areas of the body that are not white. The highest producing pigs, milk cows, and chickens are either white or partially white. In commercial pigs, the maternal sow lines are mostly white. High-producing commercially bred turkeys and chickens have white feathers and white skin. Depigmentation is both good and bad. Partial depigmentation in varying degrees appears to be highly correlated with production traits. It is interesting that the two calmest breeds of cattle the Hereford and the Holstein have completely depigmented white areas on their heads. However, excessive removal of pigment often appears in conjunction with serious developmental or neurological problems. Many veterinarians report that Holstein dairy cows that are mostly white are more difficult to handle and more nervous than Holstems with larger areas of black. Also, a genetic disorder called "white heifer disease" is commonly found in white heifers of the shorthorn breed, or in breeds related to them (Spriggs, 1946a,b; Rendel, 1952). White Shorthorn heifers are usually sterile (Spriggs, 1946a,b). The ovaries and external genitalia are normal but the uterus and the vagina are not completely developed.

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The author has observed behavioral effects correlated with with depigmentation in brown hybrid egg laying hens. Hybrid brown birds range in color from solid brown to half brown and half white. The birds have the same genetics but vary greatly in feather coloration. Solid brown birds also had stronger sleeker feathers which were not damaged by rubbing on battery cages. Birds with large areas of white coloration had weaker feathers which were more easily rubbed off the neck. Loss of feathers is a welfare concern in battery hens. There appears to be genetic factors which determine the durability of the feathers.


There is definitely a relationship between depigmentation and changes in behavior. When Belyaev (1979) selected foxes for tameness the animals also developed a piebald coat pattern with areas of depigmented white fur. Depigmentation of skin, hair, and eyes is genetically related to the development of the nervous system. Searle (1968), found a relationship between depigmentation and deafness in several rodent species. In deer mice, a relationship between the amount of white pigmentation on the head and deafness was shown by Cowling et al. (1994). The mice also had ataxia (staggering) and retinal problems, and mice with the most extensive white areas were more likely to be deaf.

Variant-Waddler is a neurological mutant strain of mice that are hyperactive and deaf, and display an abnormal circling behavior. A remarkable relationship was found between asymmetrical spotted areas of fur and the preferred direction of circling in Variant-Waddler mice (Cools, 1972a,b). The author postulated that asymmetry in the fur pattern and laterality in circling are expressions of the same basic neurological disturbance.

White cats with blue eyes are often deaf (Bergsma and Brown, 1971; Schaible and Brumbaugh, 1976). In both dogs and cats, a white or piebald coat color is also related to an increased incidence of deafness (Schaible and Brumbaugh, 1976; Sorsby and Davey, 1954). Bergsma and Brown's (1971) review of the literature discussed a continuum in the relationship between depigmentation and deafness. White cats with dark eyes or dark-pigmented areas of hair and skin on the head are less likely to be deaf, in comparison to white cats with blue eyes. Hudson and Rubin (1962) and Schaible and Brumbaugh (1976) both discuss deafness in dalmations, a heavily depigmented breed. Dalmations with the most extensive white areas were most likely to be deaf. In addition to dalmations, other extensively depigmented dog breeds such as Australian shepherds that are a pale color, have a high incidence of brain, ear, and eye abnormalities (Sponenberg and Lamoreaux, 1985; Schaible and Brumbaugh, 1976). A higher incidence of deafness and depigmentation is also found in albino cattle (Leipold and Hutson, 1962).

Depigmentation also has a detrimental effect on the visual system. Guillery (1974) reports that many albino mammals have visual pathways with crossed connections to the brain. Siamese cats which are partially albino have crossed visual pathways (Guillery et al., 1971). The crossed visual pathways do not compromise the welfare of Siamese cats kept as pets. Siamese cats are able to adapt well to their miswired visual systems (Guillery, 1974). However, visual tests more demanding than shape discrimination revealed that albinos have subtle visual perception deficiencies. Sheridan (1965) found that black and white hooded rats with pigmented eyes performed better than albinos on a test which required the rat to perform a visual discrimination task with one eye covered. The hooded rats were better able to perform the task when they had to switch eyes. This principle is also vividly shown in mice. Guillery et al. (1971) found that flecked mice with variegated areas of both pigmented and depigmented areas of skin and fur, have normal visual pathways to the brain even though they are roughly 50% albino. The white areas of skin and hair are albino and the dark areas are pigmented. The welfare of albino rats in a laboratory probably has not been compromised because they are still able to eat, drink, and mate without difficulty However, further abnormalities of the visual system may cause functional problems. The use of albinos in vision or hearing research may possibly confound the results due to abnormalities in the auditory and visual system.

Highly depigmented or albino animals are rare in nature. When they do occur, the animals generally have difficulty surviving in the wild. One brief reference in Science by Minckler and Pease (1938) refers to a colony of albino rats living under feral conditions. These rats inhabited an area at a local dump in Montana. The exact source of these animals is unknown, but it was presumed that students from the local university released them. Abundant food, water, shelter, and a lack of predators created a sheltered environment suitable for an albino colony to survive.

White cats also depend on humans to maintain them. Even dark-eyed white cats do not survive under feral conditions. Many animals with genetically based behavioral problems are often highly depigmented. Viennese white rabbits have seizures (Hohenboken and Nelihaus, 1970). In the paper on nervous pointer dogs by Dykman et al. (1969) both authors noticed that the five nervous pointer dogs in the photographs were almost all white. These dogs had greater areas of white fur than typical pointers. It would be interesting to measure the amount of depigmented areas on the bodies of both normal and nervous pointers and then compare these to Dykman et al.'s (1969) continuum of nervous traits.

The nervous excitable pigs discussed earlier are usually very lean and white or mostly white. The first author has observed possible signs of overselection for depigmentation in high-producing, commercially bred hybrid pigs. The incidence of blue eyes in terminal cross pigs is increasing. The first author speculates that they may possibly be related to the increasing incidence of nervous excitable pigs at slaughter plants. A few blue-eyed animals are not a problem, but breeding them together might cause neurological abnormalities similar to those which occur in dogs and cats. Research on rats found that albinos have more unmyelinated nerve fibers in the optic system compared to hooded rats (Lund, 1973). In albinos, the visual cortex is thinner (Lund, 1973). This is further indication of nervous system abnormalities and depigmentation.

The relationship between depigmentation, albino genes, spotting genes, and nervous system problems is documented extensively in mammals (Silversides and Smyth, 1986). The link in poultry is much weaker. Harper et al. (1988) found that the "hobbler" defect in turkeys is not linked to feather color. The birds have abnormalities in the inner ear and have difficulty balancing. However, Silversides and Smyth (1986) found a relationship between lighter feather color and congenital tremor. The affected birds had abnormal myelin in the cerebellum of their brain, and a reduction in melanin pigment in the eyes and feathers. A possible explanation for less of an effect in poultry might be due to the fact that baby chicks of the white poultry breeds are born with yellow down and adult white poultry have yellow-pigmented legs. Depigmentation of bronze-colored leghorns born with a mutation which makes some of its feathers white creates weak animals and the homozygous mutant does not survive (Somes, 1979). Photos in this paper indicate that the partially white mutants also have very pale (almost white) feet and beaks as adults. Albinism and depigmentation in most mammals causes abnormalities in the rods in the retina which are used for night vision. However, albino birds do not have retinal abnormalities (Jeffery, 1997). Unlike most mammals, birds have a cone (color-vision)-dominant retina and the development of the cones is unaffected. A few albino mammals, such as the squirrel, have relatively normal retina development because cones predominate (Jeffery, 1997).


Another possible warning sign of both genetic problems and detrimental effects of the environment on genetics is greater asymmetry of an animal's body (Markow, 1992). Asymmetry means that one side of the animal's body is larger than the other. Conservation biologists use measurements of body symmetry to assess detrimental effects of environmental pollution in Rainbow trout (Leary and Allendorf, 1989). They stress the importance of taking body measurements on several different body locations to get an accurate measure.

Asymmetry is also affected by purely genetic causes. Parsons (1990) states that inbreeding increases the degree of asymmetry in a variety of animals. Hybrid mice had more symmetrical teeth than inbred animals (Bader, 1965). In trout, fish with greater heterozygosity and gene variation were more symmetrical (Leary et al., 1983). Asymmetry also affects an animal's performance and adaptability Manning and Ockenden (1994) measured the differences in the width and length of knees, teeth, ears, coronet band, upper leg, and six measurements of the heads of race horses. They found that horses which were more symmetrical performed the best on the race track. In a study of birds, female swallows preferred males with long symmetrical tails (Moller, 1992, 1993).

There also appears to be a relationship between domestication and asymmetry. Domestic animals tend to be more asymmetrical than wild animals (Parsons, 1990). Asymmetry and minor physical abnormalities are signs of greater problems. Human children with developmental abnormalities such as mental retardation and autism have a greater percentage of minor physical abnormalities than the general population (Steg and Rapport, 1975; Links et at., 1980). They are also more likely to have greater asymmetry (Malina and Buschang, 1984). Assessments of body asymmetry may be one simple way to provide an early warning of potential problems with a selective breeding program. Dairy cow breeders for years have evaluated various body parts for symmetry. For example, dairymen routinely look at traits such as a well-formed, symmetrical udder. All major dairy bull studs do this because they intuitively know that symmetry is a good trait.

An important conclusion can be made. Overselection for a single trait ruins the animal. In breeding animals, people must be aware of the complex interaction between traits which do not appear to be related. The authors speculate that selection for a moderate amount of depigmentation appears to provide production advantages but excessive selection will cause serious welfare problems. The PIC commercial pig breeding company bred a sow line which produces all white pigs regardless of the sire's coat color. Slaughter plants prefer white animals because they are easier to dehair. The authors speculate that the offspring from these sows may be fine provided they are bred to a pigmented boar, but if they are bred to a blue-eyed white boar, there may be problems.


At what point has genetic selection in a certain trait gone too far? Changing an animal's diet or housing conditions may provide decent welfare under some conditions, but not others. There may be a point at which the animal is so defective that it will suffer even when it is fed and housed in a perfect environment. For example, most Holstein dairy cows would have good welfare when they are housed and milked in a specialized man-made environment, but their welfare in the wild would probably be poor. Dairy cows genetically selected for high milk production would not survive. If genetic selection for milk production goes too far, it is likely that the Holstein cow may develop serious health problems which cannot be compensated for by improving her nutrition or housing.

(1999 Update)

There is evidence that continuous selection for productivity is compromising disease resistance. Increasing growth rate in pigs lowers immune response to vaccination (Meeker 1987). Rothschild (1998) states that there is an antagonistic relationship between selection for production traits and selection for immune response and disease resistance.

Animals can be altered by genetic selection to such an extent that serious structural or neurological defects develop. These defects may cause great discomfort to the animal. Animals with bowed legs or other structural abnormalities may have difficulty walking. Both authors agree that animal welfare is not acceptable if high-producing meat animals are chronically lame due to weak legs. It is the opinion of both authors that it is not possible to have an adequate level of animal welfare if a selected trait becomes so extreme that it causes obvious mobility problems, or if it causes a condition that is known to be painful in humans. A good example is arthritis.

One may argue that measuring how an animal feels is very difficult. However, the nervous system of pigs and cattle has the same basic design as the human nervous system. Careful studies of different mammals reveal that surgical procedures do cause pain in animals (Short and Poznak, 1992; Molony et al., 1995). Noxious stimuli that would be likely to cause pain in people will also be likely to cause pain in animals (Short and Poznak, 1992; G. F Gebhart, quoted in Mukerjee, 1997).

Both authors suggest a criterion for determining the ethical limit for genetic selection. The first criterion is freedom from pain due to structural abnormalities or overdeveloped meat-producing muscle which causes functional problems. Female animals that are unable to give birth naturally and are forced to endure severe dystocias would have severely compromised welfare. Another example is heart attacks in pigs that are homozygous for PSS. The second criterion is low levels of abnormal behavior, such as hyperexcitability For example, hyperexcitable pigs constantly back up in races and bunch and pile up at the slaughter plant, and nervous pointers have difficulty adapting to normal dog environments. High fear levels in these animals are very aversive and severely compromise their welfare unless they are trained to tolerate novelty. The third criterion for good welfare is the relative absence of abnormal, "stereotypic" behavior. Selecting animals for excessive appetite motivation may cause stereotypies and other abnormal behaviors in feed-restricted breeding animals. Genetic selection has gone too far in the wrong direction if stereotypies develop in large numbers of breeding animals which are housed and fed under the best conditions. A fourth criterion is freedom from neurological abnormalities which interfere with the animal's mobility and basic functioning. For example, Siamese cats with mildly crossed eyes have good welfare, but animals which have been bred to have constant epileptic seizures may have poor welfare unless they are housed in an environment free of seizure triggers.


It is clear that animal welfare problems have occurred in some animals as a result of overzealous selection for a single trait. Many dog breeds have structural problems which compromise welfare, such as eye problems in collies and back problems in dachshunds (Ott, 1996). Many of the traits discussed in this chapter can be selected for without compromising welfare if selection is done in moderation. Animal breeders need to take a more holistic view when they select breeding stock. The science of genetic engineering now makes it possible to delete genes or swap genes between species. People concerned with animal welfare have stated that a major difference between conventional selective breeding and genetic engineering is that the process of selection is greatly sped up (Fox, 1989, 1992; Grandin, 1991; Rollin, 1995). The speed of change is accelerated to a point at which there will be less time to take corrective action if a selection mistake is made. To use the pig as an example, the problem with excitability in pigs has gradually become worse but has occurred slowly enough so that the pork industry will be able to change selection criteria before excitability problems become so serious that the animals are completely impossible to handle. If genetic engineering is used to produce a new superline of meat pigs a giant leap in genetic change could take place in one generation.

Transgenic pigs with the gene for human growth hormone have been developed (Purcel et al., 1989). Even though the pigs grew 15% faster than the controls they had serious infirmities. They were lethargic, lame, had an uncoordinated gait, and had joint problems. They were arthritic and had ulcers (Purcel et al., 1989). Purcel and colleagues also found that in order for these pigs to grow 15% they had to be fed a special diet which increased protein and additional lysine. Extra nutrients were required to fuel fast-growing muscle.

Genetic engineering has also been used to insert genes for various human diseases to create animal models for research. Mice altered byremoving a gene involved in the regulation of seratonin display behavior which resembles obsessive-compulsive disorder (OCD) in humans. The mice altered by genetic engineering methods ran around repeatedly in the same alley of a maze. Normal mice will quickly try a new alley (Chen et al., 1994). Hooper et al. (1987) has created a mouse model for Lesch-Nyan syndrome; children afflicted with Lesch-Nyan syndrome self-mutilate and bite themselves. If this model is developed to the point at which the syndrome is fully expressed the welfare of the mice will be severely compromised (Rollin, 1995).

It is beyond the scope of this chapter to discuss all the ethical arguments about genetic engineering, but there is a greater ethical justification to cause some suffering in a mouse if the mouse model makes it possible to cure Lesch-Nyan syndrome. This syndrome is one of the most horrible genetic conditions that can affect a child. It is the opinion of both authors that causing pain in order to make a pig grow slightly faster is absolutely not acceptable.

Genetically altering an animal by knocking out selected genes can affect the behavior of an animal in unexpected ways. Silva et al. (1992a,b) used genetic engineering methods to knock out the gene that encodes for a substance called calcium calmodulin-dependent kinase. This substance is involved in the mechanisms of learning. The "knock-out" mutants had impaired spatial learning when tested in a water maze which required them to find a platform hidden under the surface of milky-colored water. The behavior of the knock-out mice was similar to that of normal mice which had lesions in the hippocampus. The hippocampus is a structure in the brain that is crucial in forming memories.

However, it was found that knocking out this gene affected more traits than just learning how to find a platform in a tank full of water. The knock-outs also had an abnormally enhanced acoustic startle response. They were more likely to jump when they heard a sudden loud noise.

Two years later researchers in another lab made a startling discovery They found that these same knock-out mice were sometimes found dead in their cages with broken backs. It turned out that they fought so hard that they broke their backs (Chen et al., 1994). This is another example of an unexpected effect. Knocking out the gene for calcium calmodulin kinase II affected more than just learning. It also completely removed fear. This substance is also involved in the regulation of the neurotransmitter seratonin. The knock-outs had normal behavior except in the area of defensive aggression. Offensive aggression was measured by quantifying attacks by a mouse that was placed in its cage. Defensive aggression was measured by measuring how hard an intruder mouse fought a resident. Since the knock-outs had no fear they continuously attacked a resident mouse when they were placed in its cage. The heterozygote knockouts with one knock-out gene had abnormally high defensive aggression (Chen et al., 1994). Offensive aggression which is attack aggression was attenuated in the genetically engineered mutants.

Researchers in another laboratory were also surprised by unexpected results from a study in which a specific gene was blocked. Giros et al. (1996) found that blocking the effects of the dopamine (neuro transmitter gene) in mice had both predicted and unexpected results. Blocking the effect of the gene made the mice have an overabundance of dopamine in their brains. Dopamine excess is believed to be responsible for some of the symptoms of schizophrenia in people. As expected, mice which were homozygous and had two copies of the blocked gene were hyperactive and ran around more compared to the heterozygous (one copy of the gene) or normal wild type. Neither type of genetically altered mice had stereotypies. The unexpected finding was that injections of amphetamines had no effect on the homozygotes and there was an eightfold increase in locomotor activity in the heterozygotes and normal wild type mice (Giros et al., 1996). This experiment provided important insights into how pharaceuticals work and showed that the effects of drugs on behavior are not simple and straightforward.

The reason for the differential effects on offensive and defensive aggression is related to reduced fear in the mutants. Similar effects of fear may operate in mice bred and selected by conventional methods. Male mice which were bred to have heightened reactivity to stimulation were less aggresssive (Gariepy et al., 1988).


What if through the use of genetic engineering an animal was created that would feel no pain and have no fear? What would be the ethical implications of this? The work of Chen et al. (1994) showed very clearly that breeding mice with no fear caused serious welfare problems due to fighting and injury. Deleting the fear mechanism in mice created problems with severe injuries when strange mice were mixed. There may be other traits that are linked.

To a lesser degree, selecting for extreme docility with conventional breeding methods could cause similar problems. Ranchers have observed that placid Hereford bulls will spend more time fighting with other bulls to determine their social rank than flighty, excitable Saler bulls. The more excitable animals are too fearful to fight. The second author has made similar observations in horses. The calmest horse on a pasture may bully the other horses. There may be an optimum temperament between extreme docility and flightiness. Cattle and pig breeders need to select for a calm temperament and cull individuals which panic when confronted with novelty, but it may be a mistake to select for the absolutely calmest animals. A cow that is too docile may take poor care of her calf. Increased defensive aggression only occurred in mice that were heterozygous for the knock-out gene. Mice which had both calcium calmodulin kinase II genes knocked out had overall attenuated aggression and many other abnormal behaviors. The behavior differed depending on whether or not the animals had one or two knocked out genes. This research clearly shows that knocking out genes is not going to provide clear-cut results. As with natural breeding, traits are linked. The behavior of an animal is determined by a complex interaction of many inherited traits and their interaction with the environment.

In the dog, Jasper Rine and his colleagues at the Lawrence Berkley Human Genome Center have identified 13 behavior traits which are almost exact opposites in Newfoundlands and Border collies (McCraig, 1996). The most dramatic opposites were "eye" and crouching in the Border collie and attraction to water in the Newfoundland. The Border collie is a dog that depends on sight and the Newfoundland depends on its sense of smell. When these breeds are crossed some unexpected new traits, which did not exist in the parents, emerged. Several dogs started "singing" (howling) when they heard piano or country western music.


Another serious concern brought up by ethicists and geneticists is the problem of restricting the gene pool. This problem is not restricted to genetic engineering. Many scientists are concerned about the loss of genetic diversity (Notter, 1996; Cundiff et al., 1996). Larry Cundiff, a researcher who works for the U.S. Department of Agriculture, stated that the pig breeds in China have more heterozygosity and are more different than Bos taunts (British or European) and Bos indicus (Brahman) cattle. Preserving the genetic diversity of the Chinese pig breeds is important.

The loss of genetic variability in agricultural plants and animals could result in disaster if a disease struck susceptible high-producing genetic lines. Nothing is free: if one selects for just one trait there is usually a price to be paid by weakening some other trait. In 1977 the American Livestock Breeds Conservatory was founded to preserve rare breeds of domestic livestock and poultry. Some agriculturists do not see the wisdom of keeping old breeds of pigs and chickens that have low productivity The old breeds lack productivity, but they often have other desirable traits such as disease resistance, fertility, and hardiness (Thomas, 1995; Sponenberg, 1995).

The more specialized a domestic animal becomes, the more specialized an environment it will require. A Holstein cow requires more environmental support by humans than a beef cow. Beef cows and horses can still go feral and survive under wild conditions. The first author has observed feral cows on mountain ranches which were able to avoid being rounded up for up to 10 years. The Holstein milk cow with her huge udder, would have great difficulty living under natural conditions. The first author has observed that Holstein calves are weaker and take longer to walk unassisted compared to beef breed calves.

In the plant kingdom, corn is an example of a totally domestic plant. It cannot grow without assistance from humans. Modern corn is totally different than its ancestor, teosinte. Teosinte had hard kernels covered with an inedible shell, whereas modern corn has more kernels and no hard shell over them. Recent research by Jane Dorweiller at the University of Minnesota showed that changing just a small stretch of DNA was all that was required for converting teosinte into corn. Plants have been more greatly modified by domestication than animals.


One may speculate, what if an animal breed were manipulated as much as corn has been changed? Modern corn breeds look like a different species compared to wild corn. Would it be ethical to create microcephalic cows with almost no brain. Dr. Mike Fox (1989, 1992) was one of the first people to ask this question. If the nervous system was either eliminated or modified so that the mutant would not suffer, would it be ethical? We will let the philosophers fight over this one.

Being practical people with years of practical experience with animals, both authors agree that decisions on the ethical use of biotechnology should be based on the concept of ethical cost. Invasive or painful experiments or the creation of animals with chronic pain should not be done for frivolous reasons. It may be justified to cause some pain or discomfort in an animal to find a cure for AIDS, but it would not be morally justified to make animals suffer to grow larger amounts of meat or produce a few more pounds of milk.

It is our opinion that agricultural animals which are extremely excitable are not acceptable from an animal welfare standpoint. We are also very concerned about the welfare of breeding animals which have been selected to have a huge appetite. Genetically altered animals can provide tremendous knowledge about both genetics and the nervous system. If researchers take a few simple precautions, most mutants can be maintained in a laboratory with good welfare. The "no fear" mice would have an adequate level of welfare if caretakers made sure not to mix strange mice together. The homozygous mutants with hyper locomotor activity may be more compromised. Breeding large numbers of these mice probably would not be ethically justified, but breeding them in small numbers may be justified in order to learn more about the mechanisms of neurotransmitter pathways. This may help provide new medications and treatments for many serious disorders. A researcher sensitive to the welfare of the animals in his laboratory could maintain mutant breeding stock with large numbers of heterozygotes which have more normal behavior and keep just enough homozygotes for ongoing experiments.

There is a big difference between just a few hundred mice in a laboratory and thousands of pigs or chickens used for the commercial production of animal protein. Since animals on commercial farms often are not managed as carefully as research animals, genetic characteristics which may cause few welfare problems in a controlled laboratory setting could cause horrible suffering on a farm. This would be especially true if the farm was poorly managed. If a "no fear" pig was created, animal welfare on a farm could become deplorable because the animals might seriously injure each other during fights. If the aggression gene was also knocked out to eliminate fighting new problems might occur. Maybe the fearless, totally nonaggressive cow or sow would fail to take care of her babies, or maybe the totally nonemotional mutants would be too lazy to fully graze a pasture. The authors conclude that one should be more cautious when genetically altering an agricultural animal compared to a laboratory animal. Even when animals are bred naturally one must be careful that the animal will fit in its environment (LeNeindre et al., 1996). They found that cattle and sheep which have been bred for intensive conditions may have behavioral problems when housed extensively For example, cows which are gentle under intensive conditions may become aggressive toward humans when reared on large pastures.

In 1991 the first author was asked to present a paper on biotechnology and meat production (Grandin, 1991). In this paper a brief history of science was reviewed. Scientists in the past were persecuted and sometimes killed for discussing and discovering forbidden knowledge. Yesterday's forbidden knowledge is today's accepted fact. Gallileo was persecuted for writing about his finding that showed the Earth was not the center of the universe. Today genetic engineering is controversial, but tomorrow it may be routine. One should remember that in the past medical knowledge was held up for a thousand years due to prohibition against dissection. The editor of Science suggested that we must proceed with biotechnology but we should proceed with caution (Koshland, 1989). We end this chapter with the last two sentences of the first author's paper given in 1991.

"We should proceed cautiously but we should definitely proceed. Biotechnology can be used for noble, frivolous, or evil purposes. Decisions on the ethical use of this powerful new knowledge must not be made by extremists or people motivated purely by profit."


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