It may be due to poor management and poor innate resistance to disease

Which data are the basis of your question? Absolute numbers or relative amounts? Much more chickens are raised than other species in most countries, so absolute numbers can be very misleading.

Dear C.A. (Kees) Kan

In most of the diseases chickens found to be susceptible. Please see

https://edis.ifas.ufl.edu/publication/PS044

I think your question should be "why chickens in confined commercial poultry houses are more susceptible to diseases"? then the answer should be because of stressors which depress the immune system, and close proximity due to high stocking dencities. also young chickens (incomplete immue system) are more susciptible.

The fact that chickens are susceptible is to me no proof, that other species are not affected at the same rate. The publication is an extensive list of diseases, not indicating to me, which species are the most susceptible to diseases.

Chickens are kept confined in houses for commercial purpose, this condition produces stress, depress the immune system and increase susceptibility. Mortality is reported in number and in relation to other livestock in different countries, this number leads the reader as they are more susceptible but not. Chickens are raised more than other species and their number is more double to large animals, mortality rate and susceptibility should be considered with their number and genetic interval.

It is a vague question. Some diseases are genetically controlled, while some are not. In the latter case, drastic environmental forces are responsible,while in the former, genetic causes having a familial base are responsible. Timely vaccination and sound management may somewhat mitigate disease.

Continuous genetic improvement to obtain a higher body weight and a food conversion factor that reduced the immunity of broilers

Aside from prophylactic immunizations and biosecurity, most chicken viral diseases have no well-known therapeutic options. But if we consider two groups like the commercial and local breeds of chicken.

Commercial breeds have undergone continuous selection leading to a homogenous population with less genetic diversity and less potential for disease resistance.

Secondly, intensive farming requires artificial selection for commercially beneficial traits, housed in controlled environments as opposed to the local breeds that mostly undergo natural selection from exposure to various pathogens and harsh environments in the wild.

I will answer your question by mentioning backyard farming. Indeed, it is common in this type of farm to find that the animals are not vaccinated and no biosecurity measures are put in place. As a result, chickens are exposed to all kinds of diseases and can also become potential reservoirs of disease.

We also have the continuous genotypic evolution of viruses, which means that after a while, some vaccines become ineffective.

Will not they get natural immunity at least some survivors in the flock/herd? Will not such resistant ones be useful for breeding, MrAmoia,pl

Dear Loknath G.R.

Very good question!

Indeed, it is true that some chickens will manage to develop a certain natural immunity. The question is how many of them, won't the loss to the farmer be overproportional to the gain of birds that have developed a natural resistance to the virus?

Knowing that the virus develops a continuous mutation, will this gain of immuno-resistant animals be of much use in the backyard? Won't these animals be sold after a while?

I think that the development and production of recombinant thermostable vaccines more adapted to the genotypic diversity of each given region could be a solution.

They lack a complex lymphoid system like majority of animal...the have only bursa,Risk to infection increase with type of management system-free range poultry are the most susceptible, Hygiene is another influencing factor - fecal oral route is the main mode of transmission of poultry diseases,Due to their high body temperature make them vulnerable to environmental stressors eg cold weather increasing contraction of infection, limited spacing in poultry houses thus due to crowding diseases prevalence is higher, majority of infectious agent causing poultry infections are resistant to adverse environment and remain infective for long in contaminated poultry houses

Improper vaccination program as well as system of management and lack of sanitation inside poultry houses

Because of the continuous selection of productive traits, and this is inversely related to the body's immunity and exposure to diseases

In my opinion, poultry, especially chickens, suffer from diseases due to their weak immune systems, and vaccination activates part of this immune system to some extent. Therefore, proper health and nutrition management and preventing stress in them can help prevent diseases to a large extent. Also, proper ventilation and preventing crowding of chickens in one place are other factors that contribute to their health

Can we consider that rearing animals in the open air can also be a solution for strengthening the defensive qualities of the immune system of chickens?

Open air does not mean open space because it is difficult to control the temperature. It means providing the necessary oxygen and proper metabolism and other parts of the body to help strengthen the body's general system, including the immune system.

As a result of selection processes towards desirable productive traits such as body weight, immunity decreases, and birds become more susceptible to diseases