Turkey is the common name for a large gallinaceous bird with a fan-shaped tail and a bare, wattled head, which has become widely domesticated for food. The name is derived from its distinctive ‘turk-turk’ call. Turkeys show sexual dimorphism, with the male being approximately 1.5 times larger than the female. Other differences between the sexes can easily be identified during sexual displaying: the male’s head region will change colour from pink to a mix of blue, red and purple, while the female’s head region remains pink.
Wild turkeys (Meleagris gallopavo) range over North America from southern Mexico to the north-eastern USA. Their habitat is diverse, ranging from low, moist and hot coastal plains to swamps and mountains. M. gallopavo includes five subspecies of wild turkeys and all domestic varieties. Recognized subspecies are the Mexican turkey (M. g. gallopavo) of central Mexico, Merriam’s turkey (M. g. merriami) in the mountainous areas of south-western USA and northern Mexico, the Rio Grande turkey (M. g. intermedia) of Texas and north-eastern Mexico, the Florida turkey (M. g. osceola) and the Eastern turkey (M. g. silvestris), ranging from Texas and Nebraska to the Atlantic coast and the north-eastern USA.
Wild turkeys are omnivorous, with their diet consisting of a variety of berries, seeds, leaves, grasses, insects, crustaceans and small reptiles. Turkeys do not show any specialized adaptations of feeding - they exhibit the basic avian feeding pattern. It is not necessary for the bird to raise its head to swallow food, which suggests that swallowing is an active process. Drinking is accomplished differently from feeding, as the head is raised, the beak is extended upward and the beak is closed several times in rapid succession. This suggests that there is a degree of active swallowing in addition to the flow by gravity to the oesophagus.
Scratching behaviour is an important component of foraging for food, and gallinaceous birds scratch with one foot while standing on the other. Wild turkeys extend the foot forward and scratch backward and outward in a sweeping motion to form an inverted ‘V’ pattern on the ground. In domestic turkeys scratching behaviour is rarely seen on the range or in the litter provided in houses. The reduction in scratching in domestic turkeys may reflect reduced motivation associated with genetic change during domestication. Alternatively, turkeys may still be motivated to scratch but are prevented from doing so by physical constraints or inappropriate environmental provision (Hale et al., 1969).
Newly hatched poults (young birds) will peck indiscriminately at objects that contrast with the background. This response leads to the poults pecking at feed and images in the water, and so initiates feeding behaviour. Social facilitation of this behaviour is provided by other poults. If novel objects are presented to the birds, curiosity pecking is initiated, and there appears to be little evidence of neophobia as compared with chickens. The digestive tract of the turkey is similar to that of other poultry species. In turkeys, along with many species of galliform, preening and dust bathing are common compared with water bathing. Dust bathing is influenced by litter condition; it is facilitated when dry, friable litter is available. Preening is observed throughout the day, but especially just after lights on and just before lights off. Turkeys can develop problems of feather pecking and cannibalism in captivity.
Many interactions occur between individuals and groups of turkeys. Social behaviour in turkeys includes aggressive, submissive and sexually related activities, parent-offspring interactions, synchronized behaviour and competitive activity.
The social stratification of a population of turkeys is highly developed in the wild turkey (see: Hierarchy). The status of each individual is determined by the end of its first year, and usually remains fixed for life. Males are usually forced into two contests around 6 or 7 months of age when they leave the brood flock: one establishes his position within his group of siblings and the other determines the status of his sibling group with respect to other groups. Fighting consists of pecking at the head and neck. The strongest fighter in the group becomes the dominant bird, and the order of rank is established among siblings and seldom changes as long as the dominant bird lives.
Females in the group also establish social dominance through contests. When males leave the brood flock, females fight for individual rank among themselves but, unlike the males, there is not fighting among flocks (Watts and Stokes, 1971).
Wild turkeys are gregarious except at breeding time, and are polygamous. They are non-migratory, even though they are good fliers. Their breeding behaviour is based on the lek. The female builds the ground nest and will lay 8 to 15 eggs per clutch, which she will brood. At hatching the poults weigh 2 ounces (55 g) and have yellow down with usually brown markings. Within 10-12 days the first flight feathers begin to show and, by the end of the first month, all the yellow down has been replaced with plumage.
Domestication first occurred in the seed-planting culture of the Aztec Indians of Mexico. Domesticated turkeys were then brought from Mexico to Europe through Spain during the 16th century, and several European varieties have since been developed.
Fertility under natural mating conditions in commercial flocks does not have a high success rate, possibly because of the natural lek-based mating system. Genetic selection for broad-breasted strains now means that commercial males may be up to three times heavier than the females to which they are mated, and artificial insemination is therefore usually necessary (Hocking, 1993).
The average female breeding turkey is kept for over 1 year and does not enter lay until 28-32 weeks. It is necessary to rear breeding birds under high light intensities to induce them to lay. Breeding turkeys typically produce between 45 and 60 live young per year. The incubation period for a turkey egg is approximately 28 days. Once the poults are hatched they are moved to a brooder unit, when birds are placed within surrounds where feeders and drinkers are available. The purpose of the surround is to condition the poults to locate drinkers and feeders, and to ensure the birds are maintained at the correct temperature. Day-old poults are initially raised at 35°C, and this temperature is usually reduced by 1°C every 3 days until 21°C is reached. At 6 weeks of age the surrounds are removed and the poults are either given access to the whole shed or to a range, or are moved to another farm, called ‘brood and move’. Around 18 weeks female turkeys reared for meat purposes are depopulated (slaughtered) and the whole carcass is typically used. Around 21-25 weeks male turkeys used for meat purposes are depopulated, and the meat from these birds is usually cut into portions. Birds of both sexes reared for meat are called growers.
Growing and breeding turkeys reared in the UK are usually given ad libitum feed and water, although breeding birds receive diets with lower protein levels and grow more slowly than grower birds. Growers typically have three or four changes in diet, whereas breeder birds will have more changes in diet. For the first 8 weeks turkeys are fed turkey starter crumb feed, which is high in protein, and are then fed on turkey grower feed from around 8-12 weeks, and from 12 weeks to depopulation the birds are reared on turkey finisher feed, which is high in fibre and fat. In some countries no animal substance is permitted in turkey feed, so the main source of protein is from soybean.
Commercially reared turkeys are grown in a variety of housing, ranging from conventional (enclosed, controlled environment) sheds to free-range conditions. Another popular method of rearing turkeys is in a pole barn system. This allows access to natural daylight, but there is little ventilation or temperature control in these systems. Free-range systems provide the birds with access to an outside area and subject them to natural light conditions. The majority of turkeys are reared in single-sex flocks, but smaller flocks may be mixed sex.
Due to the variety of turkey-rearing systems birds may be kept in many different environments, so some of the welfare issues raised below will not be relevant to all birds. For example, there is a huge range of flock sizes of commercially reared turkeys, from a few hundred in pole range or range systems to tens of thousands in conventional houses. Different systems have various minimum available floor area guidelines, with conventional houses having a minimum of 260 cm2/kg and enclosed range areas with 10 m2/kg.
Turkeys are vaccinated against numerous diseases, administered to the birds through a variety of methods. For example, turkey rhinotracheitis live vaccine is sprayed on to the turkeys when they are 1 day old; avian encephalomyelitis live vaccine is administered to the birds in their drinking water; and pasteurella, Newcastle disease and Paramyxovirus type 3 vaccines are all administered via intramuscular injection.
Lighting used in conventional turkey houses is either incandescent or fluorescent bulbs. Turkeys reared in conventional houses are typically kept in light intensities between 1 and 10 lux as a control strategy to reduce feather pecking and cannibalism. Intensities as low as 1 lux can cause buphthalmus (enlarged eye), and increased intraocular pressure and enlarged adrenal glands (Siopes et al., 1984). Turkeys will preferentially select high light intensities while spending very little time in very low-light environments (Sherwin, 1998; Barber et al., 2002).
Another way the industry controls feather pecking is by beak trimming of birds kept in open housing where the light environment cannot be controlled. These include breeders, as they require light to stimulate lay, and turkeys reared in pole barns and extensive systems, where they are subjected to high light intensities. This practice is also known as debeaking, or partial beak amputation, and most UK turkey companies will beak trim the birds before 21 days of age, and will remove up to one-third of the upper mandible. Three main methods are used to beak trim birds: electronic trimming (bio-beaking), cold cutting (with secateurs) and hot cutting (with a cautery iron). There is no evidence that beak trimming causes chronic pain in turkeys trimmed up to 21 days old (Grigor et al., 1995). Breeding birds may be beak trimmed twice, as they are reared for over a year and it is possible that the beak may grow back.
Some turkey producers toe clip birds, either removing one, two or three toes at the junction of the first and second digit, or at the nail end. This prevents damage from scratches on the skin, which can downgrade the carcass. This may occur if the flock crowds into a small area such as a corner when startled. Back scratches may also occur during catching and transportation to the killing plant.
Males have a secondary sexual organ, the snood, which is at the base on the beak. The snood can be pulled during male fights and can be pecked by females in a mixed flock. This can cause damage and provide an area for disease entry. Some turkey producers remove the snood at 1 day old to prevent this damage from occurring. The organ is well innervated, but there is no information as to whether the snood removal process is painful or whether it leads to chronic pain.
It is important to keep the litter in a good, friable condition. Certain litter conditions can cause the development of breast blisters, which may cause discomfort to the birds and also downgrades the carcasses. Contact with ammonia or other noxious materials, including faecal enzymes in the litter, could result in breast blisters. The length of the photoperiod is also known to increase the chance of birds developing breast blisters. The longer the dark period the greater the chances of breast blister development, possibly because birds lie down for longer without moving.
Leg weakness can be a welfare problem for commercially reared turkeys (see: Bone strength). Genetic predisposition, nutrition, infection, mycotoxins, medication, husbandry practices and interactions between them have all been associated with leg weakness. Large strains usually show higher incidences of leg disorders than lighter stocks. This may be due either to weight effects or a consequence of a genetic correlation between body weight and defective bone growth (Hocking, 1993).
Sudden changes in the environment, such as the presence of a predator or rapid change in the light environment of the turkey house, can panic the birds, which may cause them to trample and damage other birds. Turkeys will ‘pile up’ against walls or in corners if startled, which can lead to smothering and death.
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