Egg Drop Syndrome (EDS) in laying hens
This disease has a great economic impact as it considerably affects production.
Diseases are aspects of vital importance, since they are the foundation for analyzing the behavior of birds and their incidence in production, in order to identify the pertinent action plans to control them in time.
The Egg Drop Syndrome (EDS) is a pathology that affects laying hens and is transmitted throughout the egg. All breeds can be infected, but it has been reported that broiler breeders and brown egg birds are more susceptible
Horizontal transmission occurs slowly in the cage system and quickly in floor laying systems in layer farms. Contaminated eggs, as well as egg trays or feces, appear to be the main sources of virus spread. However, some outbreaks have been attributed to contact with wild birds or water contaminated by feces
It is believed that the few infected hens carry latent virus and then infect other hens when they go into lay. Infected hens excrete virus and healthy hens in contact become infected. Once the flock becomes sick, horizontal contagion occurs, but the virus is not very infectious or excretion is low, so other nearby flocks may not become sick.
The disease is mainly characterized by a drop in egg production early in the laying period, or by a sudden drop in production later in the laying period.
Early on, symptoms include shelled and thin-shelled eggs, deformed eggs and, in the case of brown eggs, a loss of shell color. In addition, the whites of these eggs are very watery, and there is considerable variation in egg weight.
The most common symptoms in birds are:
Decrease in feed consumption
The crest becomes pale
Appearance of slight diarrhea
lthough the signs of EDS are quite characteristic, the diagnosis should not be made by the clinical picture alone, but should be confirmed by laboratory testing, as several infectious and non-infectious causes can lead to a decrease in egg production and can impair external and internal egg quality.
In addition, several non-infectious factors, such as stocking density, management, and feed and water quality, are implicated in egg production losses and should be taken into account.
Outbreaks of EDS typically last 4 to 10 weeks and a 10 to 40% drop in egg production can be expected. The time it takes for a bird to return to normal laying can be 4 to 8 weeks, and in many cases the production curve is below normal.
The decrease in egg production is related to the pathological effects that this adenovirus causes in the reproductive system of laying hens.
On the other hand, the virus is eliminated through the egg and day-old chicks, which makes it persistent in production. The spread of this type A adenovirus implies a greater number of affected birds during their productive stage, although it does not cause mortality.
EDS produces minimal lesions and they are limited to the reproductive tract of laying hens, where inactive ovaries, atrophy of the oviducts, and edema and white exudates in the uterus can be found.
There is no effective treatment for EDS. The prevention strategy should be based on a strict biosecurity plan, proper cleaning and disinfection of equipment in contact with eggs, especially egg trays, which are known to be a major factor in the spread of the disease, in addition to restricting the entry of visitors.
Vaccination with an inactivated virus prior to laying is especially important to prevent egg production losses and reduced egg shell quality in commercial and breeder layer flocks. Initial vaccination is done between 14 and 16 weeks of age.
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