I find interesting tidbits while browsing around. Things I did not know, and I want to remember:
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 eggshells white 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 and a decline in hatchability.

Table 1. Non-infectious causes of reduced egg production.
Nervous flock, increased pecking, feathers in digestive tract
Birds down in cages, increased incidence of shell-less eggs
Vitamin D3
Increased mortality from calcium depletion, increased shell-less eggs
Increased nervousness, increased mortality (peckouts), poor albumen quality, feather eating
Low body weight gains, drop in egg size
Increased mortality due to urolithiasis, lowered feed intake
Lower feed intake, soft bones, thin shells, increased shell-less eggs
Vitamin D3
Increased shell-less eggs, soft bones
Nervousness, mouth lesions, fatty livers, biliary hyperplasia in liver tissue, reduced feed intake, thin shell
Weakness, limp neck, neck feathers easy to pull out, prostration
Shell-less eggs, loss of pigment of brown eggs, lowered hatch, of fertile eggs
Reduced feed consumption, birds lack coordination
Out of feed
Nervous flock, decreased feed consumption
Out of water
Blue combs, birds gathered around waterers
Inadequate daylength
Unusual pattern of egg production
High ambient temperature
Reduced egg size, reduced feed consumption, increased water consumption, panting
Northern fowl mite
Nervousness, finding mites on birds (usually around the cloaca)
Nervousness, weight loss, reduced feed intake
Stick-tight fleas
Fleas embedded in the fleshy parts of the chickens's head around the eyes, ulceration and irritation of skin around the eyes
Nematodes (roundworms)
Unthriftiness, poor feed efficiency, increased mortality (in severe infestations)
Cestodes (tapeworms)
General unthriftiness, dry and unkempt feathers, hearty appetite but weight loss
Table 2. Typical diagnostic signs associated with common diseases and conditions which can cause a drop in egg production.
Fowl pox
- scab-like lesions on the unfeathered body parts (especially face and comb)
- characteristic gross lesions in the intestinal tract - higher mortality in some cases - bloody droppings
Infectious bronchitis
- coughing, sneezing, and rales - egg production drops markedly (by as much as 50%). - soft-shelled or misshapen eggs - watery egg white - poor pigmentation of brown-shelled eggs
Newcastle disease
Mild form:Acute form: - reduction in feed and water consumption- respiratory distress - dramatic drop in egg production- twisted neck - decreased shell quality - increased mortality
Avian influenza
Mildly pathogenic form:Highly pathogenic form: - listlessness- facial swelling - sneezing, coughing- dark red/white spots on legs and combs - diarrhea- respiratory distress
Avian encephalomyelitis
- seldom show clinical signs - slight, transient drop in egg production
Mycoplasma gallisepticum
- coughing, sneezing, snicks, rales, nasal and ocular discharge - decrease in feed consumption and egg production
Fowl cholera
- sudden unexpected deaths - reduction in feed consumption - swollen wattles - nasal and ocular discharge - cyanosis of head - white water or green mucoid diarrhea
Infectious coryza
- swelling and puffiness around the face and wattles - thick, foul-smelling nasal discharge - labored breathing - decrease in feed and water consumption
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An Alphabetical List of More than 60 Chicken Breeds
With Comparative Information​


According to UC Davis Veterinary Care Program:
2. Physical Characteristics (4-6 weeks of age)
a. Comb – The cockerels comb is medium size and pinkish, the pullets is small and yellowish.
b. Legs – The cockerel’s legs are sturdy and long, the pullets are finer and shorter.
c. Tail – The cockerel’s tail is stumpy and curved, the pullets is longer and straight.
d. Back – The cockerel has a thin line of stub feathers down the center of his back, the pullet has more advanced feathering along the center of her back.
e. Side of neck, flank and crop – The feathering in the cockerel in these areas is poorly advanced, the pullets feathering in these areas is well advanced.
f. Wing bows – In the cockerel the wing bows are bare, in pullets the wing bows are covered with small feathers.