The laying cycle of a chicken flock usually covers a span of about 12 months. Egg productionbegins when the birds reach about 18-22 weeks of age, depending on the breed and season. Flockproduction rises sharply and reaches a peak of about 90%, 6-8 weeks later. Production thengradually declines to about 65% after 12 months of lay. A typical production curve for a layingflock, showing changes in the level of egg production and in egg weight, over time, is giveninFigure 1.

Figure 1. 

There are many factors that can adversely affect egg production. Unraveling the cause of asudden drop in egg production requires a thorough investigation into the history of the flock. Egg production can be affected by such factors as feed consumption (quality and quantity),water intake, intensity and duration of light received, parasite infestation, disease, andnumerous management and environmental factors.

Noninfectious Causes

Aging Hens

Chickens can live for many years and continue to lay eggs for many of these years. However,after two or three years many hens significantly decline in productivity (seeFigure 2). This varies greatly from bird to bird. Good layers will lay for about 50 to 60 weeksand then have a rest period called a molt. Poorer layers and older hens will molt more oftenand lay less consistently. SeeTable 1.

Figure 2. 

Improper Nutrition

Laying chickens require a completely balanced diet to sustain maximum egg production over time.Inadequate nutrition can cause hens to stop laying. Inadequate levels of energy, protein orcalcium can cause a drop in egg production. This is why it is so important to supply layinghens with a constant supply of nutritionally balanced layer food. Feeding whole grains, scratchfeeds and table scraps will cause the birds diet to become imbalanced and inadequate.

Many times these imbalances can cause other problems like oviductal prolapse. Prolapse mayoccur when the bird is too fat and/or an egg is too large and the bird's reproductive tractis expelled with the egg. Prolapse usually causes permanent damage to the hen and is fatalin many cases.

Omission Of Feed Ingredients

Salt

Animals have an innate desire to consume salt. Feeding a salt-deficient diet will lead toincreased feather pecking and a decline in egg production.

Most animal feeds will contain added salt, usually in the form of sodium chloride. Iodineis rarely added as a separate ingredient. Instead, iodized salt is routinely used. Cobaltiodized salt is often used in diets for swine and ruminants, and this can also be used withoutany problems for poultry. This type of salt is usually blue.

Sodium is an essential nutrient, playing a major role in maintaining body fluid volume, bloodpH, and proper osmotic relationships. A continuously low intake of salt can cause a loss ofappetite. Sodium deficiencies adversely affect utilization of dietary protein and energy,and interfere with reproductive performance.

Chlorine is also an essential nutrient. Hydrogen chloride (HCl) released from the true stomach(proventriculus) is important in digestion. Chlorine also plays a role in maintaining osmoticbalance in body fluids. Birds deficient in chlorine are more nervous, showing increased sensitivityto sudden noise.

Calcium

The egg shell is composed primarily of calcium carbonate. The pullet's requirement for calciumis relatively low during the growing period, but when the first eggs are produced, the needis increased at least four times, with practically all of the increase being used for the productionof eggshells. Inadequate calcium consumption will result in decreased egg production and loweregg shell quality.

Hens store calcium in medullary bone, a specialized bone capable of rapid calcium turnover. As calcium stores are depleted, bones become brittle. In severe cases, hens are unable tostand. The condition is known as caged-layer fatigue. Birds on the ground or on litter floorsrecycle calcium and phosphorus through consumption of feces, and do not have caged-layer fatigue.

Calcium can be supplied in the diet as either ground limestone or oyster shell. Particlesize affects calcium availability. Usually the larger the particle size, the longer the particlewill be retained in the upper digestive tract. This means that the larger particles of thecalcium source are released more slowly, and this may be important for the continuity of shellformation, especially in the dark period when birds do not ordinarily eat.

Periodically, dolomitic limestone is offered to the feed industry. However, dolomitic limestone(which is used in the steel industry) should never be used in poultry diets. Dolomitic limestonecontains at least 10% magnesium, and this complexes with calcium or competes with calcium forabsorption sites in the intestines. The consequence of feeding dolomitic limestone is inducedcalcium deficiency.

Young birds should not be fed a high calcium layer diet because the calcium/phosphorus ratiowill be unbalanced, resulting in increased morbidity or mortality.

Vitamin D

Vitamin D is required for normal calcium absorption and utilization. If inadequate levelsof vitamin D are fed, induced calcium deficiency quickly results and egg production decreases.

Feed grade vitamin D comes in two forms, D2 and D3. In most animals, both are equally potent. In birds, however, D3 is substantially more active than D2. In poultry diets, therefore, vitamin D must be supplied in the form of D3.

Protein

Dietary requirements for protein are actually requirements for the amino acids that constitutethe protein. There are 22 amino acids in body proteins, and all are physiologically essential. Poultry cannot synthesize some of these, or cannot synthesize them rapidly enough to meetthe metabolic requirement. Therefore, these amino acids must be supplied in the diet. Aminoacid requirements vary considerably according to the productive state (i.e., growing, layingeggs, etc.), age, type, breed, and strain. Methionine is the amino acid most often deficientin laying rations.

When pullets begin laying, there is an increase in protein, vitamin and mineral requirementsper day due to deposition in the egg. If dietary protein is too low or the amino acid requirementsare not met, poor egg production and hatchability will occur.

Fat

Dietary fat is a source of energy and of linoleic acid, an essential fatty acid. A deficiencyof linoleic acid will adversely affect egg production. Dietary fats also serve as "carriers"of fat-soluble vitamins, and some fat is necessary for absorption of vitamins. In fact, impairmentof the absorption of fat-soluble vitamins (A, D, E, and K) is the most serious consequenceof a dietary deficiency of fat.

Toxicoses

Salt

Although the salt requirement of birds is relatively low, adequate levels are essential, andexcessive amounts are highly toxic and reduce egg production. Birds require a sensitive balancebetween necessary and toxic levels of salt. SeeTable 1.

Excess dietary salt intake readily causes wet droppings and wet litter. Several feed ingredients,such as fish meal, corn gluten meal, meat meal, whey and sunflower meal contain high levelsof sodium. When such ingredients are used, the level of supplemental salt (NaCl) in the dietmust be reduced.

Phosphorus

The nutritional role of phosphorus is closely related to that of calcium. Both are constituentsof bone. The ratio of dietary calcium to phosphorus affects the absorption of both these elements;an excess of either one impedes absorption and can reduce egg production, shell quality and/orhatchability.

In addition to its function in bone, phosphorus plays a primary role in carbohydrate metabolism,is active in fat metabolism, and helps to regulate the acid-base balance of the body.

Vitamin D

Excess vitamin D3 leads to increased calcium absorption resulting in hypercalcemia which may reduce egg production.Most animal species appear to be able to tolerate 10 times their vitamin D3 requirement for long periods of time. For short-periods of time, poultry can tolerate upto 100 times their requirement. An excess of vitamin D3 in the diet, therefore, is unlikely.

Mycotoxins

Molds can produce mycotoxins which adversely affect egg production and general health. Theycan interfere with the absorption or metabolism of certain nutrients, depending on the particularmycotoxin. Apparent calcium and/or vitamin D3 deficiencies can occur when mycotoxin contaminated feeds are given to laying hens. In addition,some have hormonal effects which can cause a decline in egg production.

The major mycotoxin of concern with corn is aflatoxin, produced by the moldAspergillus flavus. The mold infects corn both in the field and in storage. Aflatoxin fluoresces under ultravioletlight, so its presence can be detected by examining grain under "black light". Othermycotoxins sometimes associated with corn and other grains are zearalenone (F-2 toxin), ochratoxin,T-2 toxin, vomitoxin, and citrinin. More than 300 mycotoxins have been identified.

Botulism

Botulism is an acute intoxication caused by consumption of a neurotoxin produced by the bacteriumClostridium botulinum. It commonly occurs when birds consume decomposing carcasses, spoiled feed or other decayingorganic materials. Ponds and other stagnant water sources are often areas of decaying materialsthat may contain this toxin.

Other toxins

Numerous plants are toxic to varying degrees if plant parts or seeds are consumed by the bird. Production, hatchability, growth, and livability may be reduced. Examples of these plantsinclude crotalaria, nightshade, coffeeweed, cotton seeds, chick peas, vetches, and many ornamentals.Other potential causes of problems include pesticides, herbicides, disinfectants, fertilizers,drugs, antibiotics, and other chemicals, including oils and antifreeze.

Anticoccidials

Anticoccidials (to prevent coccidiosis) are commonly used in diets for replacement pullets,meat birds and young breeding stock that are reared on litter floors. Anticoccidials are notgiven to commercial laying hens.

Nicarbazin

Nicarbazin is an anticoccidial drug that reduces reproductive performance when it's inadvertentlyadded to layer or breeder diets at normal anticoccidial levels. The yolk membranes are weakened,resulting in mottling of the yolk. Nicarbazin fed to brown-egg layers turns their eggshellswhite within 48 hours, although this is completely reversible when the product is withdrawnfrom the feed. Even low levels of nicarbazin can cause some loss in shell color, mottlingof egg yolks (see Fact Sheet PS-24, "Egg Quality"), and a decline in hatchability.

Monensin

Monensin has been the most successful of the anticoccidials. Monensin, and other ionophoreanticoccidials, have an adverse effect on egg production when used in conjunction with lowprotein diets.

Management Mistakes

Out of feed

If hens are out of feed for several hours, a decline in egg production will probably occur. The amount of decline will be related to the time without feed. Be sure that all the birdshave access to an adequate supply of a complete feed which meets all their nutritional requirements.

Feed stored on the farm longer than two weeks may become moldy. If feed becomes wet it shouldbe discarded. In addition, vitamin potency decreases with prolonged storage.

Out of water

Water is often taken for granted, and yet it is probably the most essential nutrient. Wateris by far the single constituent of the body, and, in general, represents about 70% of totalbody weight. Access to water is very important, and a lack of water for several hours willprobably cause a decline in egg production. Hens are more sensitive to a lack of water thana lack of feed.

The amount of water needed depends on environmental temperature and relative humidity, dietcomposition, and rate of egg production. It has been generally assumed that birds drink approximatelytwice as much water as the amount of feed consumed on a weight basis, but water intake variesgreatly, especially in hot weather.

Inadequate daylength

Hens need about 14 hours of daylength to maintain egg production. The intensity of light shouldbe sufficient to allow a person to read newsprint at bird level. The decreasing daylength duringthe Fall and shorter daylengths in the Winter would be expected to cause a severe decline,or even cessation, in egg production unless supplemental light is provided. When productionceases, the birds may also undergo a feather molt. Hens exposed to only natural light wouldbe expected to resume egg production in the Spring.

High house temperatures

High environmental temperatures pose severe problems for all types of poultry. Feed consumption,egg production, egg size, and hatchability are all adversely affected under conditions of severeheat stress. Shade, ventilation, and a plentiful supply of cool water help reduce the adverseeffects of heat stress.

Ectoparasites

An ectoparasite is a parasitic organism that feeds on the exterior of the body of the host.

Northern fowl mite

The northern fowl mite (Ornithonyssus sylviarum) is the most common of the poultry mites. Refer to the publication PS-10, ("Common ContinuousExternal Parasites of Poultry"), for information on identification and control of Northernfowl mites.

Northern fowl mites are blood suckers and are irritating to poultry. Anemia occurs in heavilyparasitized birds, reducing feed efficiency, egg production, and ability to withstand and overcomediseases.

Lice

Several species of chewing lice may be found on chickens, especially those in small flocksor on range. Refer to publication PS-10, ("Common Continuous External Parasites of Poultry"),for information on identification and control of lice.

Chicken lice feed on dry scales, feathers, or scabs on the skin. As lice crawl over the bird,their mouth parts and sharp claws scratch the skin. The constant irritation causes the birdto become nervous and behave abnormally, causing a general unthriftiness and unkempt appearancein the bird. Egg production in infested flocks may drop as much as 10%, although some heavyinfestations have caused egg production to fall as much as 20%.

Fleas

Stick-tight fleas are sometimes a severe problem in home flocks and may be difficult to preventor eradicate. The adult female flea attaches to the skin around the face and head, causingsevere irritation and, in some cases, blindness. Refer to publication PS-10, ("CommonContinuous External Parasites of Poultry"), for information on identification and controlof stick-tight fleas.

Endoparasites

An endoparasite is a parasite that lives and feeds inside the host animal.

Heavy infestations of endoparasites can cause unthriftiness, poor feed efficiency, poor growth,reduced egg production, and mortality in severe infestations. Infected birds may also be moresusceptible to various diseases and stresses.

Nematodes

Nematodes, or roundworms, are elongated, cylindrical, unsegmented endoparasites. There aremany species of roundworms, each tending to infect a specific area of the gastrointestinaltract. Refer to publication PS-18, ("Nematode Parasites of Poultry"), for identificationand control of nematodes.

Tapeworms

Tapeworms (cestodes) are white or yellowish ribbon-like segmented flat worms. They vary insize from 0.17 to 12 inches in length. Although tapeworms do not produce extensive lesionsor damage to the intestines, they are nutritional competitors. A cestode does not digest itsown food. Instead, it anchors itself to the inner wall of the bird's intestines, letting itssegmented body dangle in the flow of digested material, absorbing nutrients before they canbe utilized by the host. A variety of commercially available anthelmintics will effectivelyand safely eliminate both nematodes and cestodes from poultry.

Diseases

Fowl Pox

Fowl pox is a viral disease of chickens characterized by scab-like lesions on the skin of theunfeathered body parts and/or on diphtheritic (wet) membranes lining the mouth or air passages. Infection with the fowl pox virus will cause the chickens to have poor growth, poor feed conversionand a precipitous fall in egg production. Fowl pox may affect any age bird. It is transmittedby direct contact with an infected chicken or by mosquitos.Table 2.

For more information on fowl pox, refer to publication VM66, "Prevention and Control ofFowl Pox in Backyard Chicken Flocks".

Coccidiosis

Coccidiosis is a protozoan disease characterized by enteritis and diarrhea in poultry. Unlikethe organisms which cause many other poultry diseases, coccidia are almost universally foundwherever chickens are raised. Coccidiosis outbreaks vary from very mild to severe infections.SeeTable 2.

Individual strains of cocci attack birds differently, resulting in diverse symptoms. The overallsymptoms may be one or more of the following: bloody droppings, high mortality, general droopiness,emaciation, a marked drop in feed consumption, diarrhea and a drop in egg production in layers.

It is common to add a coccidiostate in the feed of broilers. In addition, live vaccines arecurrently available.

Infectious bronchitis

Infectious bronchitis is a highly contagious respiratory disease. The disease is caused bya virus which is moderately resistant, but can be destroyed by many common disinfectants.

Infectious bronchitis occurs only in chickens (Infectious bronchitis is different from Quailbronchitis which affects Bobwhite Quail). All ages of chickens are susceptible to infectiousbronchitis. In laying hens it is characterized by respiratory signs (gasping, sneezing, coughing)and a marked decrease in egg production. Egg quality is also adversely affected. Low eggquality and shell irregularities (soft-shelled or mis-shapened) may persist long after an outbreak.Chickens that have had infectious bronchitis, especially during the first week of life, maynever be good layers.

There is no effective treatment for infectious bronchitis, although broad spectrum antibioticsfor 3 to 5 days may aid in controlling secondary bacterial infections. Vaccines can be usedfor prevention, but they are only effective if they contain the right serotypes of virus fora given area. Infectious bronchitis vaccine is often combined with Newcastle vaccine in thesame vial.

Newcastle disease

Newcastle disease is caused by a virus. The viruses vary in pathogenicity and are classifiedas lentogenic (mildly virulent), mesogenic (moderately virulent), and velogenic (markedly virulent).

Newcastle disease is characterized by a sudden onset and rapid spread through the flock. Inadult laying hens clinical signs can include depression, loss of appetite, decreased waterconsumption, and a dramatic decline in egg production. Production may drop to zero. Newcastledisease runs its course in 10 to 14 days, but the hens do not come back into full productionfor 5 to 6 weeks.

There is no treatment for Newcastle disease. Antibiotics can be given for 3 to 5 days to preventsecondary bacterial infections. Chickens and turkeys can be immunized against Newcastle diseaseby vaccination.

Avian influenza

Avian influenza is a viral disease affecting the respiratory, digestive and/or nervous systemsof many species of birds. Avian influenza viruses are classified based on severity of disease,ranging from apathogenic to highly pathogenic. The mildly pathogenic form produces listlessness,respiratory signs (sneezing, coughing), and diarrhea. The level of mortality is usually low. The highly pathogenic form of avian influenza produces facial swelling, cyanosis, and dehydrationwith respiratory distress. Dark red/white spots (cyanosis/ischemia) develop on the legs andcombs of chicks. Mortality can range from low to near 100%. The decrease in egg productionis related to the severity of the disease and can be severe.

There is no specific treatment for avian influenza. Recovery is rather spontaneous. Birdsslaughtered 7 days after infection often have no significant increase in condemnations.

Infected flocks will be quarantined by the State. Quarantine is continued until the flockis depopulated. The course of the disease is 10 to 14 days, but recovered birds continue toshed the avian influenza virus in feces for 3 or 4 weeks. Eggs from layers are safe to eat,but the shell should be wash and sanitized. The poultry litter or manure should be compostedbefore application to cultivated lands.

For more information on avian influenza refer to publication PS-38, "Avian Influenza inPoultry".

Avian encephalomyelitis

Avian encephalomyelitis (epidemic tremors) is a viral disease usually affecting young poultry. It is characterized by incoordination and tremors, especially of the head and neck in chicks,and elevated mortality levels. Chicks that recover may later develop cataracts after sexualmaturity. In affected hens, decreases in egg production and hatchability are noted.

Laying hens seldom show clinical signs when infection is going through the flock. However,good production records often reveal a slight drop in egg production (5 to 20%) lasting nomore than two weeks. In breeding flocks, a corresponding decrease in hatchability is alsonoted.

There is no effective treatment. All replacement breeder and layer pullets should be immunized.

Mycoplasma gallisepticum infection

Mycoplasma gallisepticum infection (chronic respiratory disease, PPLO infection, airsacculitis, MG) is characterizedby respiratory distress (coughing, sneezing, snicks, rales, discharge from eyes and nose).Feed consumption and egg production decline in laying hens. Mortality is usually low but theremay be many unthrifty birds.

The organism may be present in a flock and cause no disease until triggered by stress, e.g.,changes in housing, management, nutrition, or weather.

Many broad spectrum antibiotics have been used for treatment and will suppress losses. However,relapses often occur when treatment is discontinued. Most antibiotics are given in feed orwater, preferably in water. Tylosine and tetracyclines have been used extensively for treatment. Injectable antibiotics may be more effective if the disease is advanced and if the flock issmall enough to be treated individually. FDA withdrawal periods for respective medicationsused must be strictly observed to avoid residual chemicals in the eggs and meat. Live and inactivatedvaccines also are commonly used to reduce the adverse effects of the disease.

Fowl cholera

Fowl cholera is an infectious bacterial disease of poultry. With an acute outbreak, suddenunexpected deaths occur in the flock. Laying hens may be found dead on the nest. Sick birdsshow anorexia, depression, cyanosis, rales, discharge from eyes and nose, white watery or greenmucoid diarrhea, and egg production is decreased.

As fowl cholera becomes chronic, chickens develop abscessed wattles and swelling of jointsand foot pads. Cheesy pus may accumulate in the sinuses under the eyes.

Flocks can be treated with a sulfa drug. Sulfa drugs are not FDA approved for use in pulletsolder than 14 weeks or for commercial laying hens. Sulfa drugs cause residues in meat andeggs. Prolonged use of sulfa drugs is toxic and causes a decrease in production in layinghens. Antibiotics can be used, but require higher levels and longer medication to stop theoutbreak.

Where fowl cholera is endemic, live and/or inactivated vaccines are recommended. Do not startvaccinating for fowl cholera until it becomes a problem on the farm and a diagnosis is confirmed.

Infectious coryza

Coryza is a respiratory disease of chickens. Common clinical signs nclude swelling and puffinessaround the face and wattles, a thick sticky discharge with a characteristic offensive odorfrom the nostrils, labored breathing, and rales. There is a drop in feed and water consumptionas well as egg production.

Sulfadimethoxine (Albon) is the preferred treatment for infectious coryza. If Albon failsor is not available, sulfamethazine, sulfamerazine, or erythromycin (Gallimycin) can be usedas alternative treatments. The sulfa drugs are not FDA approved for pullets older than 14weeks or for commercial laying hens.

A vaccine for infectious coryza is available. It is given subcutaneously (under the skin)on the back of the neck. Chicks are usually vaccinated four times, starting at 5 weeks ofage (i.e., at 5, 9, 15, and 19 weeks with at least 4 weeks between injections). Vaccinate againat 10 months of age and twice yearly thereafter.

Other Problems To Consider

There are a variety of other problems which can cause an apparent drop in egg production.They include:

1. Predators and snakes consuming the eggs.
2. Egg-eating by hens in the flock.
3. Excessive egg breakage.
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