Laying Hens Laying Drop? Watch Out for These Four Viral Diseases

I. Newcastle Disease
1. Overview: An acute, highly virulent infectious disease that chickens of all ages are susceptible to, characterized mainly by diarrhea, difficulty breathing and neurological symptoms. It can be divided into four types: peracute, acute, subacute and chronic. Peracute and acute Newcastle disease have a short onset time and high mortality; it is the subacute and chronic forms that have a relatively large impact on egg production, sometimes also called atypical Newcastle disease. Flocks with atypical Newcastle disease generally show respiratory symptoms: sick chickens cough, have rales, difficulty breathing, swollen eyelids, shrunken combs with a purplish color, and sometimes pass yellow or green watery droppings; in severe cases egg production drops by 20%-30%, sometimes by more than 50%. Egg quality decreases, with more white-shelled eggs, soft-shelled eggs and deformed eggs; when the egg is opened, the albumen is as thin as water.
2. Necropsy: Congestion or hemorrhage of the trachea, individual chickens with swollen sinuses, shedding of the proventricular mucosa, hemorrhage or swelling of the papillae, and in severe cases hemorrhage in the gizzard as well. Extensive hemorrhage in the duodenum and small intestine; the jujube-pit-shaped ulcerative hemorrhage in the small intestine has typical diagnostic significance. Diffuse hemorrhage in the rectum, and enlargement and hemorrhage of the cecal lymph nodes also have diagnostic significance. In laying hens the yolk is purplish or congested, and in severe cases there is metritis or salpingitis.
3. Countermeasures: Emergency vaccination with ND strain IV vaccine, 3-4 doses per bird. To prevent secondary E. coli infection, antibiotics can be given in drinking water for 3-4 d.
　　
II. Avian Influenza
1. Overview: Avian influenza (A1) is an acute, highly contagious infectious disease caused by type A virus. This disease can occur in all four seasons, regardless of breed or age, and is especially common in cold seasons. Birds, humans and lower mammals are all susceptible to type A influenza virus. The clinical symptoms in flocks infected with avian influenza are diverse and can be divided into respiratory, nervous and reproductive types, etc. Sick chickens have an elevated body temperature and are depressed; they cough, have rales, tear up, and their face and head swell, while the comb, wattles, skin and scales on the toes turn purplish; they pass yellow and white watery droppings, egg production drops, and deformed eggs, faded eggs and soft-shelled eggs increase; some also have neurological symptoms.
2. Necropsy: Edema of the head and cyanosis and congestion of the wattles, comb and legs; edema and congestion of the tracheal mucosa, with serous or caseous exudate; swelling of the sinus cavities, swelling and thickening of the air sacs with fibrinous or caseous exudate; enlargement and necrosis of the liver and spleen; ulceration and hemorrhage of the proventricular papillae, extensive hemorrhage in the intestinal tract; swelling and congestion of the follicles, congestion of the oviduct, sometimes accompanied by yolk peritonitis.
3. Countermeasures: There is currently no effective chemical drug for treating this disease; quinolone drugs can be used to prevent bacterial infection. Prevention should be the main focus at ordinary times, and in epidemic areas oil-emulsion inactivated vaccine should be used for immunization. Affected flocks should be culled.
　　
III. Egg Drop Syndrome
1. Overview: This disease occurs mainly in laying hens and young pullets; chickens of other ages can be infected but show no symptoms, and it is also seen in flocks at the peak laying period of 25-34 weeks of age. At onset, the sick chickens' spirit, feed intake, water intake and droppings are basically normal, while egg production drops severely day by day. The eggshell color becomes lighter or a large number of thin-shelled eggs, soft-shelled eggs, shell-less eggs and deformed eggs appear. It generally lasts about 3 weeks, then slowly recovers, at a rate that varies, and sometimes it may also return to the original level.
2. Necropsy: EDS-76 lacks characteristic lesions; sometimes chickens develop catarrhal enteritis, ovarian atrophy or hemorrhage, inflammation of the uterus and oviduct, white exudate in the oviduct lumen, and edema, pallor and thickening of the mucosa.
3. Countermeasures: Vaccination with EDS oil-emulsion inactivated vaccine before the start of laying can prevent the occurrence of this disease. Cull virus-carrying sick chickens and do a good job of disinfection and hygiene.
　　
IV. Infectious Bronchitis
1. Overview: Infectious bronchitis (1B) is an acute respiratory disease, highly contagious, characterized mainly by tracheal rales, coughing and sneezing. At present it is divided into respiratory, renal, reproductive and proventricular types of infectious bronchitis, etc.
(1) Flocks infected with the reproductive type of infectious bronchitis have respiratory symptoms and a drop in laying rate, along with soft-shelled eggs, deformed eggs, rough-shelled eggs, pale-colored eggs and white-shelled eggs; the albumen is watery and easily separates from the yolk. In severe cases it can lead to yolk peritonitis.
(2) The respiratory type of infectious bronchitis, accompanied by the renal type of infectious bronchitis, presents with diarrhea and, in severe cases, damages the kidneys; urate is no longer excreted with the droppings, causing urate deposition, that is, visceral gout.
(3) Chickens with the proventricular type of infectious bronchitis progressively lose weight, have ruffled feathers, stand still, have drooping wings and reduced body weight, and sometimes have respiratory symptoms, showing coughing, rales, etc.
2. Necropsy: In sick chickens, there is serous or catarrhal exudate in the trachea, nasal passages and sinuses, cloudy air sacs with yellow caseous exudate, and edema of the proventricular mucosa; chickens with proventriculitis have severe enlargement of the proventriculus, obvious thickening of the proventricular wall, and in a few cases ulceration and hemorrhage of the mucosa, as well as hepatic congestion and enlargement, slight splenic swelling, and pulmonary congestion; there is mucus in the trachea with annular hemorrhage; the follicles are congested, hemorrhagic or atrophied, the oviduct is shortened, and the mucosa becomes thick and rough; the kidneys are enlarged and pale, with the renal tubules and ureters filled with urate; the rectal mucosa shows strip-shaped hemorrhage, and there is a large amount of lime-like watery droppings in the cloaca.