Natural History, Husbandry and Social Structures Series 1

Transcription

1 Featured Case Natural History, Husbandry and Social Structures Series 1 Feeling a little chicken about caring for these increasingly popular pets? Let s dive into this particular avian world on the practical veterinary care of domestic chickens. Contributing Authors: Alicia McLaughlin, DVM, and Kendal E. Harr, DVM, MS, DACVP Backyard poultry flocks have become popular in recent years. Depending on the owner, chickens in backyard flocks may be production animals or pets, and desire for medical services fluctuates accordingly. Veterinarians are expected to provide care for these birds, regardless of prior experience, especially in certain parts of the country. To meet standards of care, veterinarians should have a working knowledge of basic anatomy, husbandry, common diseases and legalities involved with medical treatment of these animals. 12

2 BACKYARD CHICKENS: NATURAL HISTORY, HUSBANDRY AND SOCIAL STRUCTURES Natural history of domesticated chickens All chickens are descended from the red junglefowl (Gallus gallus; RJF), which was domesticated more than 5,000 years ago (Figure 1). 1 When the natural history and behavior of the domestic chicken s ancestry is understood, it is easier to optimize its habitat. Wild RJFs live in bamboo forests in Southeast Asia. These animals are highly social and follow well-developed dominance hierarchies within each flock. At least 24 vocalizations are used to communicate with flock members. 2 Males tend to be aggressive toward one another, particularly during breeding season. RJFs are omnivorous, and forage for a myriad of plants and insects by pecking and scratching through leaf litter on the forest floor. They roost in trees at night to avoid predators. Wild RJFs interbreed and produce fertile offspring with modern chickens a conservation concern for the species. 3 Over the centuries, domesticated chickens have been used as fighting animals and meat and egg producers. Many breeds of domestic chicken (Gallus gallus domesticus) have been developed and selected for characteristics that include egg production, meat production, physical characteristics, and behavior. Some breeds are highly specialized and not well-suited for lives as production animals in backyards. Others are dual-purpose bred for both egg and meat production. Best husbandry practices The most critical part of keeping a chicken flock healthy is providing the birds with adequate husbandry and preventive medicine. Many health problems can be avoided by providing appropriate environment, social structure, and nutrition. Housing. Backyard chickens are generally housed in free-range systems, with access to both a covered shelter (coop) for protection against predators and an outdoor yard for foraging. Battery housing is a system used for various animal production methods, but primarily for egg-laying hens. The name arises from the arrangement of rows and columns of identical cages, sharing common divider walls, as in the cells of a battery. ( Battery_cage) Battery cages will not be discussed here. Although freeranging chickens are exposed to various potential health risks (e.g., predators, parasites, disease), this lifestyle provides the birds with valuable mental stimulation and exercise often lacking in battery housing. By providing an environment in which natural behaviors can be expressed, stress, self-mutilation, and cannibalism are significantly less likely to occur. Wide open fields are not preferred habitats for chickens. They prefer ranging areas with trees, away from bright sun. They tend to stay close to a house or seek tree cover. 4, 5 Perching at dusk, either in trees or in a coop, is a strongly motivated behavior pattern based in predator avoidance. Most lost chickens will find their way home at dusk to roost with their flock mates. Chickens are generally inactive at night; during the day, flocks also will engage in intermittent synchronized rest periods. Advise clients to select chicken coops made of durable materials and insulated from drafts. At the same time, the coop must be well-ventilated, without providing access to predators. The interior should be easy to clean, both nest boxes for laying eggs and perches should be available. Wire-mesh substrate is not recommended because of risks of pododermatitis. Straw, hay, or wood shavings (not cedar shavings) can be provided as substrate within the coop, and should be changed regularly. Depending on geographic location, it may be necessary for clients to provide supplemental heating within the coop during winter. Although chickens are relatively cold-tolerant, if temperatures dip below freezing, they can develop frostbite or other health problems. A heat lamp or ceramic heater can provide additional warmth. (Of course, heating sources should be carefully placed to prevent accidental burns and fire hazards.) In severe weather, clients should ensure that water sources do not freeze to prevent potentially life-threatening dehydration. Some facilities also provide supplemental lighting within the coop in the winter to help prolong hens laying cycles. Predation. The most common predator of backyard flocks in the United States is the raccoon. Stray or pet dogs and cats also commonly attack chicken. Certain species of snakes are attracted to eggs, and birds of prey occasionally target backyard flocks. Uncommon predators include coyotes, foxes, opossums, mustelids (e.g., weasels, skunks, stoats) and bobcats. Although rodents are more commonly seen as disease-carrying pests, they also may steal eggs or chicks in addition to eating chicken feed. Advise clients that preventing predation can be difficult. Chicken owners should regularly and carefully monitor their enclosures for potential access points and lock the birds in the coop every night. Because traditional latches can be opened by clever raccoons, padlocks may be required. To prevent predators from digging into the coop, clients should place a pavement slab base under the coop and/or bury wire mesh around the enclosure perimeter. They should place hardware cloth or wood between the chickens and wire mesh in night roosts to prevent raccoons from reaching in and grabbing chickens through the mesh. Raccoons can rip out staples, so screws and washers and other heavy-duty hardware should be used to fix these protective structures in place. Zoning requirements may detail standards for chicken structures, and should be followed in order to obtain permits required by law. Nesting. In the wild, a hen preparing to lay eggs usually moves away from the flock to find a secluded nesting place (Figure 2). Clients should provide backyard flocks with nesting boxes and a covered nesting area, preferably within the coop. Chickens generally choose not to lay eggs in dirty nest boxes. There are individual and breed differences in nesting requirements among wild and domestic poultry, and choice is influenced by experience and social factors. 6 Behavior. The main activities of free-range hens are grazing, ground pecking, ground scratching and dust bathing. Behavior expression is weather-dependent. 7 Free-range chickens will spend time foraging for food even when poultry feeds are provided ad libitum. 8 This may result in intoxication with ground contaminants such as leaves and pine needles and any debris in the coup. Gastrointestinal impaction due to ingestion of debris in the enclosure is commonly seen. Dust bathing is a natural behavior that functions to help maintain healthy plumage and control ectoparasites. Chickens will scratch and bill-rake at the ground, then squat with their feathers erected. To thoroughly coat itself with dust, a chicken CONTRIBUTING AUTHORS FEATURED CASE 13

3 BACKYARD CHICKENS: NATURAL HISTORY, HUSBANDRY AND SOCIAL STRUCTURES Figure 1. Red junglefowl (Gallus gallus) is the evolutionary ancestor of the domestic chicken. will exhibit several behaviors, such as wing-shaking, headrubbing, bill-raking, scratching, and side-rubbing. This may take up to 20 minutes. After its bath, the bird shakes itself vigorously and preens. When allowed free access to appropriate substrate, chickens typically dust bathe at least every other day. They are more likely to dust bathe in the middle of the day, in warmer weather, if they see other birds dust bathing, or if they have been denied access to a dusty substrate. 9 Birds that are denied access to dust will sham dust bathe, suggesting the behavior is highly motivated and has important welfare benefits. Chickens are naturally highly social animals, and should be housed in a flock. Domestic chickens are commonly housed in flocks of hens with no roosters, often due to local ordinances forbidding rooster ownership because of noise concerns. If rooster(s) are kept, it is important to have a high hen-to-rooster ratio (ideally, only one rooster should be kept per small flock) to help minimize conflicts. Birds within the flock will establish a dominance hierarchy that may change over time. It is important for owners to monitor flock behaviors, as occasionally individual chickens can become dangerously bullied to the point of being denied access to food or water, or being seriously injured. Roosters tend to fight each other, and may aggressively harass hens during breeding season. Within the flock hierarchical structure, subordinate hens are often bullied, particularly when seeking nest boxes. 10 This can be minimized by providing an adequate number of nesting boxes from which to choose; typically, two nesting boxes for every four or five chickens. Some hens are highly motivated to reproduce, and when they are reproductively active (e.g. going broody ) they will attempt to steal chicks or eggs from other hens. Nutritional concerns Poultry convert feed into food products quickly and efficiently. Their high rate of productivity results in relatively high nutrient needs. Poultry require the presence of at 14

4 BACKYARD CHICKENS: NATURAL HISTORY, HUSBANDRY AND SOCIAL STRUCTURES Figure 2A. An RBJ nesting in underbrush (natural substrate). CONTRIBUTING AUTHORS FEATURED CASE Figure 2B. A domestic hen mimicking RJF behavior by seeking a secluded dark nest box. The dual nest box provides choices for the hens and prevents aggression and bullying. 15

5 BACKYARD CHICKENS: NATURAL HISTORY, HUSBANDRY AND SOCIAL STRUCTURES least 38 nutrients in their diets in appropriate concentrations and balance. Detailed information on age-dependent nutrient criteria for both meat and laying birds is available elsewhere. 11 Criteria used to determine the requirements for a given nutrient include growth, feed efficiency, egg production, prevention of signs of deficiency and quality of poultry product. These requirements assume the nutrients are in a highly bioavailable form, and they do not include a margin of safety. Nutrient requirements may be surprisingly high. For example, meat birds require 3,200 kcal/kg daily, and egg layers require 5 percent of their ingested diet to be calcium alone. Dietary adjustments should be made based on production and bioavailability of nutrients in various feedstuffs. A margin of safety should be added based on changes in rates of feed intake due to environmental temperature or dietary energy content, genetic strain, husbandry conditions (especially the level of sanitation), and the presence of stressors, including infectious diseases and other illnesses. Chickens allowed access to a yard will forage extensively for themselves and may consume myriad plant and animal material; however, that should be considered supplemental to the diet offered, rather than a staple. Hens mobilize massive amounts of calcium from their skeletons when producing eggs. As a result, hypocalcemia is a real threat in egg-laying birds, even when they are provided a calcium-rich diet. Magnesium, phosphorus and vitamin D are also very important. A high-quality pelleted feed formulated for laying chickens, with oyster shell added as an additional mineral source, will meet energy and calcium requirements for most laying hens. 11 Clients may feed clean egg shells back to the chicken but break the egg shells into small pieces so that the chicken do not realize that their own eggs may be a food source. Advise clients that, although frequently difficult to provide, chickens should have ready access to clean water at all times. Because water sources are easily contaminated, they must be cleaned frequently to minimize risk of disease spread and maximize usage. Gastrointestinal impaction seems to be common in certain backyard flocks, and likely revolves around substrates and lack of clean water as causative factors. Although some owners add bleach tablets to the water source to help reduce microorganism load, this is not advisable. Ingestion of chlorine may have deleterious health effects, and birds may refuse to drink tainted (yes chlorine as well as dirty water) water. Though challenging, providing a clean water system is the best option. Chicken owners often want to provide supplemental food items to break up the routine of their flocks diets. However, table scraps may or may not be appropriate. Healthy treats include small pieces of vegetables or fruits and bugs, including mealworms or crickets. Onions, garlic, avocado, chocolate and alcohol should be avoided because of potential toxicity risks. It is common for backyard pet chickens to become severely obese. This can lead to many of the same disease conditions seen in obese people and animals, including hepatic lipidosis and cardiovascular disease. Obesity can be assessed by both visual and tactile methods. Due to the thin skin layers in avian species, clinicians may see yellow fat pads under the skin of fat birds. This is abnormal, especially in laying hens, and indicates obesity. When palpated, the keel should be moderately prominent in most laying hens. If the keel is indistinct, the animal is obese. Monitoring body condition score is recommended. Stay tuned: Future installments of this series will cover preventive and production medicine, legalities associated with food animal practice, and treatment of common diseases. Alicia McLaughlin, DVM, is an associate veterinarian at The Center for Bird and Exotic Animal Medicine in Bothell, Washington. drmclaughlin@theexoticvet.com Kendal E. Harr, DVM, MS, DACVP, is a clinical pathologist and quality assurance specialist at URIKA in Bothell, Washington. drharr@urikapathology.com Sidebar: Which breed is that? Familiarity with common breeds of domesticated chickens enables the veterinary practitioner to better address production, behavior and nutrition-related etiologies common in background flocks. Good resources include Oklahoma State University s Poultry Breeds website (ansi.okstate.edu/breeds/poultry/ index.htm) and the American Poultry Association (amerpoultryassn.com), which have pictures of common breeds and descriptions. References 1. Storey AA, Athens JS, Bryant D, et al. Investigating the global dispersal of chickens in prehistory using ancient mitochondrial DNA signatures. PLoS ONE 2012;7(7):e Collias NE. The vocal repertoire of the red junglefowl: a spectrographic classification and the code of communication. Condor 1987;89: Fernandes M, Sathyakumar S, Kaul R, et al. Conservation of red junglefowl Gallus gallus in India. Int J Galliformes Conservation 2009;1: Dawkins MS. Behaviour as a tool in the assessment of animal welfare. Zoology 2003;106(4): Jones TA, Donnelly CA, Dawkins MS. Environmental and management factors affecting the welfare of chickens on commercial farms in the United Kingdom and Denmark stocked at five densities. Poult Sci 2005;84(8): Mills AD, Wood-Gush DG. Pre-laying behaviour in battery cages. Br Poult Sci 1985;26(2): Hughes BO, Dun P, McCorquodale CC. Shell strength of eggs from medium-bodied hybrid hens housed in cages or on range in outside pens. Br Poult Sci 1985;26(1): Nicol C, Dawkins MS. Homes fit for hens. New Scientist 1990;125(1708); Olsson IAS, Keeling LJ. Why in earth? Dustbathing behaviour in jungle and domestic fowl reviewed from a Tinbergian and animal welfare perspective. Appl Anim Behav Sci 2005;93: Appleby MC, Walker AW, Nicol CJ, et al. Development of furnished cages for laying hens. Br Poult Sci 2002;43(4): Poultry. In: The Veterinary Merck Manual, Available at: merckmanuals.com/vet/poultry.html. Accessed Jan. 11,