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CHAPTER 1
Keeping Chickens Healthy
Healthy chickens are a joy to behold. They are bright-eyed, alert, curious, and lively as they chase butterflies or scratch in the soil and peck at a bug, a blade of grass, or a seed of grain — all the while vocalizing over their accomplishments. They regularly visit the feeder and drinker, take dust baths, groom their glossy feathers, stretch out to enjoy the warm sun, and take frequent catnaps. At dusk they flock inside to settle on the roost side by side for the night.
Even while a chick is growing within the egg, it has the beginnings of an active immune system that continues to develop after the chick hatches. Along with other natural defenses, the chicken's strong immune system helps it resist disease as long as the bird remains in a wholesome environment: one that is clean, free of hazards, and safe from predators; one that provides adequate space, light, ventilation, fresh water, and suitable feed; and one that protects the flock from unnecessary stress.
The Nature of Disease
Disease is a departure from health, and it includes any condition that impairs normal body functions. Disease results from a combination of indirect causes that reduce resistance — in other words, stress in one form or another — and direct causes that produce the actual disease.
Direct causes of disease may be divided into two categories: infectious and noninfectious. Noninfectious diseases result from things other than an invading organism, such as nutritional problems (deficiency or excess), poisons, traumatic injury, or even excessive stress.
Infectious diseases result from invasion of the body by another living organism — bacteria, viruses, fungi, protozoa, and a variety of internal and external parasites. Some are always present but cause disease only under certain circumstances, such as when a chicken's resistance is weakened because of stress. Such microbes are called opportunists.
A few microbes produce disease wherever they occur. They are commonly known as germs, although technically they are pathogens and are described as being pathogenic. Variations in virulence among different strains of a specific pathogen can cause the same disease to appear in different degrees of severity or even in different forms altogether.
Reservoirs of Infection
Regardless of a disease's cause, before you can effectively control it, you need to know how the disease is introduced into a flock and how it spreads among the chickens. Diseases are introduced from reservoirs of infection, which can be any source or site where disease-causing organisms survive or multiply and from which they may be transferred to a susceptible host — in this case, a chicken. A reservoir of infection may or may not be another living being.
A chicken can serve as its own reservoir of infection, as occurs when a disease is caused by a microbe that normally lives on or in a chicken's body without causing disease. Examples are streptococci and Pasteurella bacteria, both of which infect a chicken after its resistance has been weakened by some other cause. A sick chicken is, of course, a reservoir of infection, as is also an infected dead chicken that is pecked by other hens.
Some disease-causing organisms, such as the infectious bronchitis virus, are species specific to chickens, meaning they affect only chickens and no other type of animal. Other diseases may be shared by more than one species of poultry. Sometimes microbes that are harmless to one species can be devastating to chickens. One such microbe is the Marek's disease virus, which is common and harmless in turkeys but potentially deadly to chickens.
A reservoir of infectious microbes that affect chickens need not be some type of poultry. It might be a wild bird, or an exotic or cage bird kept as a household pet. Or it might not be a bird at all. Other pets, livestock, or rodents and other wild animals, even humans, can be reservoirs of an infectious disease that affects chickens. Salmonella bacteria is an example of a microbe that infects a wide variety of vertebrates, including humans. A few infectious organisms that parasitize chickens spend part of their life cycles living in arthropods — fleas, mites, ticks, lice, and mosquitoes — and can spread disease to chickens through those creatures' bites.
Inanimate reservoirs of infection are nonliving objects that harbor disease-causing microbes. Among them are accumulated droppings, litter, soil, dust, and feed or water in which an accumulation of pathogens survives or thrives.
When a chicken falls ill, knowing where the disease came from — the reservoir of infection — can help you control the disease and prevent future occurrences. You also need to know how the pathogen got from the reservoir of infection into the chicken.
Disease Happens
The vast majority of microbes are either harmless or actually beneficial. Beneficial microbes may live either on a chicken's skin or within its body, aiding digestion and/or enhancing the bird's immunity by fending off pathogenic microbes, a process known as competitive exclusion. (For more on this subject, see Probiotics and Prebiotics.)
Given the opportunity, however, some organisms that normally live on or in a healthy chicken can multiply to the point that they become harmful. Such an opportunity most commonly occurs in a chicken with an immune system that has been somehow weakened, perhaps by poor nutrition, a parasite overload, or excessive stress.
In contrast to these opportunistic organisms, other disease-causing organisms are primary pathogens. These organisms are not commonly found in the typical poultry environment, but when they arise from a reservoir of infection, they are capable of infecting a chicken with a perfectly healthy immune system.
Such an organism enters the chicken by being inhaled into the bird's respiratory system or taken into its digestive system with feed or water. Or the pathogen might be on or burrow into the chicken's skin, scales, or feathers, or invade the body through an open wound.
How Diseases Spread
Once introduced into an individual chicken, a disease may or may not be capable of spreading to other chickens. A disease that is caused by a primary pathogen is more likely to be contagious than one caused by an opportunistic organism. Brooder pneumonia, for example, is caused by opportunistic fungi and does not spread from chick to chick, while ringworm is caused by a primary pathogen and is contagious.
A contagious disease can spread either vertically or horizontally. Vertical transmission always involves direct contact between the infected chicken and the one that becomes infected. Horizontally transmitted diseases may be spread by either direct or indirect contact.
Vertical transmission is the spread of a disease from an infected hen to her eggs, and subsequently to chicks that hatch from the infected eggs. Some viruses can be vertically transmitted to chicks from an infected cock through the semen that fertilizes a healthy hen's eggs.
Horizontal transmission is the spread of a disease from one chicken to another by means other than from an infected breeder to offspring through eggs that hatch. Horizontally transmitted diseases don't necessarily require direct contact between a healthy chicken and a sick one.
Direct and Indirect Contact
Direct contact occurs when an infected bird and a susceptible bird mate with, peck, or preen one another. Diseases that spread through contact with the skin of an infected bird include pox and influenza (caused by viruses) and staphylococcal and streptococcal infections (caused by opportunistic bacteria). Staph and strep infections also spread through mucus-to-mucus contact during mating.
Indirect contact occurs when pathogens are mechanically transported from a reservoir of infection to a chicken that becomes infected. As with reservoirs of infection, modes of transportation can be either animate or inanimate. However, here the animal or object doing the transporting is not itself the original source of infection but is merely giving the pathogen a ride from one place to another. Logically enough, an object that gives a pathogen a lift is called a vehicle.
Vehicles of Transmission
Animate vehicles of transmission are living beings, which might be wild birds, rodents, household pets, or other animals that transport pathogens on their feet, feathers, or fur (as distinct from diseased animals that are reservoirs of infection, spreading disease through their saliva or droppings). Flies and other arthropods can transport pathogens on their feet or bodies (as distinct from infected arthropods that spread disease by injecting contaminated saliva). Humans can transport pathogens on their clothing, shoes, hair, or hands when they visit each other's flocks, travel from flock to flock to inspect or vaccinate, make deliveries, or attend a poultry show.
Inanimate vehicles of transmission are nonliving objects on which pathogens are transported from one place to another. They include shed skin, feathers, droppings, broken eggs, and other debris from infected birds. These bodily discharges can be transported to healthy chickens in contaminated feed or water. They might also be transported by air, which wafts dust, fluff, fine bits of dried droppings, and droplets of respiratory moisture expelled by breathing, sneezing, or coughing. Luckily, most airborne infections don't spread far.
A common vehicle is a single needle used for flockwide vaccination or blood sampling of both infected and susceptible birds. Reused items, such as egg cartons, feeders, drinkers, and tires (of a car, truck, tractor, mower, or wheelbarrow), are other objects to which body discharges containing pathogens may cling and be transported.
In veterinary jargon any inanimate object on which a pathogen hitches a ride is called a fomite, from the Latin word fomes, meaning tinder. A pathogen can travel on a fomite for hundreds of miles before setting off a new disease outbreak.
Biosecurity
Biosecurity encompasses all precautions you take to protect your flock from infectious diseases. The fewer precautions you take, the greater the risk that sooner or later a disease will affect your chickens.
On the other hand, no set of biosecurity measures, no matter how strict, is 100 percent foolproof in preventing disease. The best you can do to protect your flock is to follow a well-thought-out program of interrelated measures that are grounded in old-fashioned common sense. Your biosecurity program should include the following measures:
* Start with healthy chickens.
* Feed them a balanced ration (discussed in the next chapter, in Chicken Feed).
* Maintain a flock history.
* Provide a sound environment.
* Routinely clean their housing.
* Disinfect as necessary.
* Keep a closed flock, or quarantine newcomers.
* Exclude wild birds.
* Minimize stress.
* Medicate only as necessary.
Acquire Healthy Chickens
Maintaining a healthy flock is difficult unless you start out with healthy chickens. The best way to make sure new birds are healthy is to purchase locally, so you can see whether or not they come from a healthful environment. You can then ask the seller, eye to eye, about the birds' ages and health history, and you can see for yourself if any of the seller's birds show signs of diseases that might be carried by the birds you plan to buy.
You'll have the least chance of getting diseased birds if you start with newly hatched chicks. The older the bird, the more disease problems it has been exposed to. If you do purchase older chickens, take your time inspecting them. Make sure they have glossy plumage, look perky and active, and don't show any signs of stress behavior (see Stress Management).
Flocks and hatcheries enrolled in the National Poultry Improvement Plan are certified to be free of several serious infectious diseases (see NPIP, below). Unfortunately, you may not find a member who has the kind of birds you want.
Don't buy any chicken unless you are completely satisfied with its background in terms of genetics, management, sanitation, and health history. Above all, avoid chicks or grown chickens from live-bird auctions, flea markets, wheeler-dealers, traders, uncertified hatcheries, and any other source where chickens are brought together from far-flung places.
Keep a Flock History
A flock history is essentially a diary that documents anything and everything pertaining to your flock. Start it the moment you acquire your first chickens, noting the date (or date of hatch — if you purchase by mail, it will be on the shipping carton), source, strain (if known), anything the seller tells you about the birds and their history, and any health certificates that come with them.
Document your feed source(s), feeding and management practices, and any changes you make as you go along, including vaccinations you give and medications you use. Write things down as they occur, rather than trusting your memory to reconstruct events should you later need the information to help trace a health problem.
You don't need to make elaborate notes. In most cases, the date, along with a few key words, should be sufficient. The Flock History table lists some of the information that would be vital should your chickens come down with an infectious disease.
A Sound Environment
The way you house your chickens can influence their continuing state of health. Most poultry housing falls into one of the following categories:
* Cage confinement — favored for show birds and pedigreed breeders
* Confinement housing — favored for fast-growing broilers, breeder flocks, and floor-managed layers
* Range confinement — favored for pasture-raised broilers and sometimes layers
* Free range — favored for laying flocks where sufficient forage is available
* Coop and yard — the most common method used for urban and suburban flocks, and others where space is limited
Chickens raised on an industrial scale are confined entirely indoors for several reasons, among them that lighting can be strictly controlled, air can be filtered, water systems can be easily medicated, and diseases that are spread by flying insects and wild birds can be more effectively excluded. If there is a major problem, the manager will remove all the chickens, clean and disinfect the facilities, and then bring in an entirely new flock.
While confined flocks are protected from some diseases, as a trade-off they incur other health issues due to lack of sunshine, fresh air, and activity. In addition, if a contagious disease does manage to get into their crowded environment, it spreads like wildfire.
Backyard chickens typically have more space to roam, as well as having access to fresh air and sunshine. They not only develop stronger immune systems, but pathogens that might wander in are more likely to get diluted by air and space.
By far the most common method of housing backyard chickens is in a coop constructed in a fixed location, with a fenced run attached. The challenge in keeping chickens healthy in such a situation is that microbe and parasite populations accumulate over years of constant use. Therefore, the single most important feature of any chicken facility is ease of cleaning. If cleanup is a hassle, you won't do it as often as you ought, and your chickens will suffer for it.
Floors
A coop's flooring influences its ease of cleaning. Several different types of flooring are common in backyard coops.
A dirt floor is simple and cheap, and it keeps birds cool in warm weather. Its disadvantages are that it's colder in winter, does not exclude burrowing rodents, and cannot be effectively sanitized.
A wood floor invariably has cracks that get packed with filth, and most are too close to the ground, providing a hiding place that invites invasion by rodents. (For more on rodents, see Rodent Control.)
Sheet linoleum covering a wood floor is a popular option in small and suburban coops because it's easier to clean than plain wood. The chief disadvantages are that it may not hold up under repeated cleanings, and bored chickens may take a notion to peck it to pieces. (For potential toxic issues, see Vinyl Flooring.)
A droppings pit fashioned from wooden slats or welded wire covering a boxlike pit may be set up directly beneath the nighttime roost, where most poop accumulates, or it can cover the entire coop floor. It has the advantage that poop will fall through, where chickens can't pick in it. The pit must be periodically cleaned out before the accumulated droppings reach the slats or wire.
A droppings board is a smooth shelflike surface suspended beneath nighttime roosts. The collection of overnight poop is then scraped off each morning. The disadvantage is that cleaning the board is a daily chore. The advantage is that you will become well acquainted with your chickens' droppings and can readily detect any changes in appearance or odor. For more information on examining droppings, see Intestinal Disorders.
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Excerpted from "The Chicken Health Handbook"
by .
Copyright © 2015 Gail Damerow.
Excerpted by permission of Storey Publishing.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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