General Chicken Information BEHAVIOR Chickens are highly social animals that develop a pecking order or social hierarchy. The rooster is the most dominant animal and the hens sort out their pecking order based on size and aggression. Once the pecking order has been determined the flock as a whole will do many activities together such as foraging, dust bathing and preening. The foraging behavior remains strong even in large commercial operations where the chickens are fed a very concentrated and nutritious diet. Their food requirements are met in a very short period of time but they will still spend much of the day pecking, probing and flicking with their beaks and scratching with their feet. A good producer should allow this behavior to occur unimpeded. Domestic chicks are very precocial when they hatch and will quickly learn to eat and drink even without the aid of the mother hen. Most commercial operations either hatch their own chicks or get them as day olds and they have few troubles as long as the food and water are obvious. Maintaining the high body temperature is difficult for the young chicks and they require a very high ( 32 C) environmental temperature to prevent hypothermia from occurring. Aggression towards people is usually restricted to the rooster who may fly at or attach anything he preserves as a threat to his flock. Roosters may have spurs on their feet that can inflict damage on intruders. Hens that are sitting on eggs to be hatched may peck at anyone that tries to remove the eggs. Most times chickens will try to avoid people and keep as much distance as possible between them. ANATOMY AND PHYSIOLOGY Dentition Chickens have no lips, cheeks or teeth instead they have two horny growths on the upper and lower mandible that is used to pick up food and is known as the beak. The upper mandible is attached to the skull while the lower mandible is hinged to allow for selectively picking up pieces of food. There is a dagger shaped tongue with a very rough surface that helps to move the food into the esophagus. Digestive System Birds have developed a unique digestive system that helps to compensate for having no teeth and therefore not being able to break down food particles in the mouth. The crop is an extension of the esophagus before it enters the body cavity. It is basically a storage pouch that allows the bird to quickly consume a meal and then let it digest throughout the day. Once the food leaves the crop it enters a structure that is truly unique to the birds, known as the gizzard. The gizzard is made up of two very powerful muscles separated by a very thick wall. When the gizzard is empty it remains inactive but as soon as food arrives it goes into action. The food enters the gizzard and the two muscles start contracting which will break the pieces of food into small particles. The gizzard will usually contain abrasive material such as grit or gravel that helps to grind the food before passing into the intestinal tract. The gizzard plays the role of the teeth in other animals by breaking large pieces of food into small particles suitable for digestion. In wild or free-range birds the gizzard is very effective at grinding up seeds and plant material but in the commercial facilities the food passes through the gizzard very quickly. The small intestine is the major site of nutrient absorption while the large intestine is responsible for maintaining the water balance in the bird. The alimentary tract ends at the cloaca, which means “common sewer.” The digestive, urinary and reproductive tracts all empty into the cloaca. The urine of chickens is mostly uric acid and is seen as a white pasty material that is evacuated with the feces from the cloaca. Thermoregulation Chickens have a fairly high body temperature (41.5 C) that in adult chickens is maintained by a high metabolism and a good insulating layer of feathers. Feathers are unique to birds and are composed of the same protein as scales, keratin. Birds are thought to have evolved from the reptiles and they still retain reptile-like scales on their legs and feet. Feathers do more than provide insulation, they also: 1) Aid in flight 2) Protect the bird from rain and snow 3) Provide camouflage from predators 4) Help attract the opposite sex of the same species Day old chicks do not have feathers to help them conserve heat and great care must be taken so that the young birds do not suffer from chilling. If the hen is present when the chicks hatch she will crouch and allow the chicks to huddle against her underneath her wings to share body warmth. This behavior demonstrated by the hen is known as brooding. The time spent brooding the chicks is greatest during the first week of life and slowly tapers off as the chicks get older. If the chicks are hatched out in an incubator, ambient temperatures of 32 C should be present for the chicks during the first week of life. The chicks’ behavior is the best indicator of proper temperature, chicks will huddle together in a big pile if they are too cold and spread out away from the heat source if too warm. As the chicks get older the temperature can be lowered until the bird is fully feathered when the temperature can be maintained at about 18 C. Chickens have no sweat glands and must rely on panting and vasodilation in the legs and comb to rid the body of excess heat. Reproduction Chickens like all other birds are oviparous, their young develop outside of the body in hard-shelled eggs that must be incubated. The incubation period for a chicken egg is 21 days and when under a hen the eggs are turned regularly and kept at the appropriate temperature and humidity. In a commercial incubator the egg is kept blunt end up at 37.6 C and 60 % humidity for 19 days and rotated on a regular basis. The last two days the egg is kept on its side at 37.2 C and 75 % humidity. Once a hen is 20 weeks of age she will begin to lay eggs by continually releasing ovum into the oviduct all year long. If semen is present the ovum is fertilized and an egg will form which can then be incubated and produce a new chick. If no semen is present the ovum is released and goes on the form an infertile egg that will not form a chick no matter how long the egg is incubated (rotten eggs). Roosters are cued by the changing daylight to begin mating with the hens. There is no physiological reason to breed the hens it is just the roosters’ natural behavior to continually mate until the daylight hours change again. Hens will crouch when approached by a rooster and copulation will occur. The semen from the rooster enters the cloaca and then travels up the oviduct where it is stored at semen storage sites until it is needed for fertilization. The stored semen can fertilize ovum as they are released into the oviduct for 15 days but a hen is usually mated again in that time. When group housed a single rooster can service up to 10 females and ensure fertile eggs. Artificial insemination can be used in laboratory settings when the background information such as disease status and vaccination program is needed for the next generation. Turkeys are quite often artificially inseminated as the large tom is not always able to mount the hen and if he does will quite often inflict injury. In a commercial setting the chickens are kept at short day conditions (8 hours light, 16 hours dark) until they are 20 weeks of age. They are then photo-stimulated by changing the light pattern to 12 hours light and 12 hours dark. This change in light cycle will induce the hens to lay and the roosters to breed As long as the light cycle remains the same or the daylight hours increase the hens will continue to lay eggs and the rooster will continue to breed. Unlike mammals, in birds it is the female that will determine the sex of the resulting embryo once mating has occurred. The rooster is homozygous and designated ZZ while the female is heterozygous and designated ZW. All birds grow and develop very quickly once they are hatched. Birds such as the quail, chicken and ducks hatch young that are precocial or nidifugous. This means that they are born with feathers and are capable of both locomotion and some degree of thermoregulation soon after they are born. An altricial or nidicolous bird hatches out young that are naked, unable to walk or thermoregulate. Examples of altricial birds include hawks, eagles and pigeons. Senses Chickens have a high density of cone receptors in the retina suggesting that color vision is important to the chicken. Newly hatched chicks have an unlearned preference for the orange and violet colors that aid them in food detection while foraging. The eyeball of the chicken is flatter than the mammalian eyeball and is capable of very little movement. The field of view is 300 degrees for the chicken but is only capable of 26 degrees of binocular vision directly in front of the head. The chicken compensates for this narrow range by having a very flexible neck and performing frequent head movements. Hearing is relatively good in chickens but is not an overly important sense for the animal. The chicken has few vocal sound patterns for communication and relies mostly on vision to detect predators. The sense of smell is very poor in the chicken and appears to be relatively unimportant to behavior. The chicken can distinguish between salt and bitter substances and will reject solutions with even small amounts of these compounds. Chickens will avoid salty solutions which makes it important to supply clean, fresh water at all times to ensure optimal production performance. Taste sensitivities tend to be greater for liquids than solids as most foods are swallowed whole and have little contact with the few taste buds that are present on the tongue. HUSBANDRY AND ENVIRONMENT Housing Commercial barns used for housing poultry have been designed to house large numbers of animals and reduce the manual labor as much as possible. Most barns will house many levels of chickens often stacked 3 or 4 layers high. Each cage is supplied with an automatic watering system and an automatic feed delivery system that is often computer controlled. If it is a layer barn there is a system of conveyor belts that will bring the eggs to a central washing and packing area. The temperature, humidity and lighting are often computer controlled or on automatic timers with a back up power system in case of emergency. Chickens can be either housed in cages or on the floor. Layers are usually kept in cages and meat birds can be housed either in cages or on the floor. There are advantages and disadvantages to both types of housing. The advantages of cages are: 1) Birds are separated from their feces, this provides a more sanitary environment. 2) It is easier to observe and care for the birds, no birds are underfoot. 3) Eggs are cleaner. 4) Chickens in cages consume less feed. 5) Internal parasites and other diseases are lessened or eliminated. 6) More birds can be housed in a given space. 7) Labor requirements are reduced and working conditions are improved. The disadvantages to using cages for housing are: 1) The investment per bird is usually higher. 2) The handling of manure can be difficult. 3) Flies can be more of a problem. 4) The bones of the caged hens are more fragile and easily broken. 5) Stress levels can be higher in the caged animals. If space permits floor housing is often used to house meat producing birds. Day old chicks can be housed in cardboard rings with a suitable bedding and an extra source of heat (heat lamp or radiant heater). As the chicks get older the cardboard ring is taken out and the chicks can have the run of the barn. The bedding used should be absorbent, light, inexpensive and non-toxic. The bedding absorbs moisture and insulates the chicks from the cooling effects of the floor as well as providing a cushion between the bird and the floor. There are a number of types of bedding that can be used to house chickens such as: 1) Wood shavings and sawdust 2) Crushed corn cobs 3) Chopped straw or hay 4) Recycled paper 5) Sand When using the floor for housing the chickens it is common to use an all-in, allout type of management style. With this system a complete clean out of the manure and disinfection of the barn will occur before a new batch of chickens is introduced. The new chickens live and grow in the barn until they are shipped to market at which time the barn is again completely cleaned and disinfected. The advantages of using this method of housing are: 1) Disease organisms are much easier to remove when there are no living animals present 2) No new birds are introduced into the established group, this reduces the chance of introducing disease or causing behavior problems. 3) The uniformity of age within the group increases the immunity to disease. 4) Easier to clean and disinfect an empty barn, as well as maintain equipment. No matter if the chickens are housed on the floor or in cages the other environmental parameters to consider are the light cycle, temperature, and ventilation. For the first 2 to 3 days of life chickens are exposed to 24 hours of light to ensure that they find the water and feeding systems. The daylight hours will then become constant until the producer wants them to start laying eggs. Temperature in a brooding barn should be kept at 32 C for the first three days and then decreased as the chicken becomes fully feathered. The chicken can then be maintained at a constant temperature that should be kept between 18 –20 C. The ventilation system in the barn should be able to remove the large amounts of dust, moisture and ammonia created by the chickens. The system must also supply fresh, clean air at a low velocity so as not to cool the chickens. A ventilation system should deliver 4-7 cubic meters of air per hour per kg of bodyweight in the barn. There are a number of systems that will work but the main concern is to have a backup system in place in case of emergency. High density housing of chickens produce huge amounts of dust and ammonia and if they are not removed can quickly lead to health problems or overheating. Chickens housed in the lab will also have a number of options depending on what type of trial is being conducted. In most cases the housing used in the lab should match the style used in commercial operations. For example a food trial for broilers should be conducted in as close to a commercial broiler environment as possible, probably floor housing. If a layer bird trial is being conducted than a layer caging system should be used in the lab setting. Cages may also be necessary if fecal collection is required for the study. The environmental conditions should be easy to control in the lab and feed and water systems should again match that of the commercial operations. Nutrition Poultry nutrition is a very complex, highly specialized business and there is continual work going on trying to create the ultimate chicken diet. For producers a diet that is inexpensive but still makes a chicken grow fast is ultimate goal. The high level of research that has been done in poultry nutrition means that there are very good commercial diets available for all types and ages of poultry. Depending on what types of birds are being raised will determine what kind of diet is to be fed. All chicks for the first 6 weeks of life require a high protein diet (19-23 %) that will allow for quick growth. After 6 weeks the layer chickens should receive 1618 % protein in the diet and the broilers should get 14-16 % protein. The layers require the higher amounts of protein for the high energy requirements of egg laying. Protein used in the diets will come from fishmeal, meat meal or vegetable proteins (soya bean). Synthetic amino acids may be added to improve the quality of the diet if a poorer source of protein is used. The complete balanced rations can be fed as pellets, crumbs or a dry mash. The crumbs are partially ground up pellets that are the right size to ensure that the newly hatched chicks consume plenty of food. Pellets are fed to birds that need a high consumption rate and are quick growers such as the broilers. A mash ration will be fed if over-consumption is a concern, as the mash takes much longer for the chicken to consume. Circular feed pans are often used to feed chickens as they provide a greater feeder space than linear feeders. One circular pan 33 cm in diameter should provide sufficient feeder space for 50 to 75 birds. If linear feeders are used 4.5 cm of trough space per bird is required. Water is perhaps the most important nutrient for an animal to consume, a chicken can survive weeks without food but only a few days without water. Broiler chickens during their lifetime (60 to 70 days) will consume 18 pounds of water and just 10 pounds of feed. For a rough estimate the daily water consumption can be calculated by multiplying the age the bird in days by 0.2 ounces. Daily water consumption is required as the drinking water is often used to deliver medication, vaccines, vitamins and electrolytes. Identification Metal wing tags are the most popular means of individually identifying chickens. The numbered tags can also come in different colors to help keep track of different groups of chickens. The tags are clipped onto the wing web of the bird with a small pair of specialized pliers. The wing web is a piece of skin that is formed between the wing tip and the shoulder. The tag should not be placed into the muscle of the wing as this can damage the bird. This is a very permanent and harmless means of identification if properly attached. Leg bands that are numbered and colored may also be used but there is much more growth in the leg than the wing and may have to be removed to accommodate growth of the leg. Non-toxic spray paint or wax crayons may be used to temporarily mark birds. USES IN THE LAB Chickens have lots of good characteristics that make them suitable for use in biomedical research: 1) Easy to house either on the floor or in cages 2) Small size makes them easy to handle and work with 3) Can be obtained as disease-free stock from suppliers 4) Genetically well defined 5) Produce an embryo that develops outside of the hen for all but the first 24 hours. Easy to monitor fetus development A lot of the research work done with chickens concerns avian physiology or pathology and has direct relevance to the health and management of domestic poultry. , Feed trials, vaccine studies, product testing and disease study are all done to improve conditions and the welfare of meat and egg producing chickens. The chick embryo provides a unique specimen to not only observe how a fetus develops but also to see how immunity can be passed on through virus research. The developing chick is also used to study all the disease causing agents, pharmacology, nutrition, endocrinology and tissue transplantation. Vaccine production and diagnosis of infectious diseases that can affect man are made possible by using cell culture techniques using the chick embryo. Although the chicken differs anatomically and physically from humans the knowledge that we have gained from these birds is immense. Since 1929, ten Nobel prizes have been awarded to investigators using chickens as the research subject. It is thought that over 2% of all abstracts from most research journals have chickens as the research subject. The importance of chickens as a research animal is immense and covers all areas of investigation.