Disease agents are the most contributors to early chick mortality. Some of these agents are imported from the hatchery along with the chicks. As a matter of fact, no hatchery in Nigeria produces a 100% disease free chick hence the need exposing chicks to antibiotics and vitamin for the first one week of life. The biggest cause of disease outbreak in a flock is the extremely contaminated farm pens and environment and poor biosecurity. Most farmers unknowingly allow disease to build up in their farm environment because of their unhygienic way of handling and disposing old litter materials.
Poor biosecurity measures will expose the flock to disease agents. Chicks have poorly developed immune system and this exposure can be lethal to them wiping of a good percentage if not all of the flock in their first few weeks of life.
Generally speaking, disease agents responsible for early chick mortality can be grouped into four (4) major groups which are;
Bacterial diseases: These are infections caused by bacterial challenge. Some examples bacterial diseases responsible for early chick mortality are:
Omphalitis: This is an inflammation of the navel. This is usually a result of poor navel healing as consequence of poor hatching condition. With optimal heat during brooding, this should not cause a heavy mortality, but it becomes a huge challenge if bacterial contamination sets in especially E. coli. Affected chicks usually present inflamed skin in the navel area, soft, flabby and distended abdomen, vent pasting, foul smelling on carcass opening, due to unabsorbed yolk.
Pullorum: This is caused by Salmonella pullorum. It is an acute infectious and fatal bacterial disease of chicks characterized by ruffled feather, white diarrhea, labor breathing, chirping and death.
Colibacillosis: It is an acute septicemia disease caused by E-coli affecting all ages characterized by involvement of all systems, poor feed conversion and death.
Viral disease: These are group of infection caused by viral agents. Some examples viral diseases responsible for early chick mortality are: Gumboro, Newcastle disease, fowl pox etc. Gumboro is a highly contagious disease of young birds usually between the ages of 3-6weeks but is sometimes seen in adult birds. It causes serious mortality and morbidity. It can wipe out 70-80% of an affected flock. Prevention through vaccination is the best way to prevent loss due to this infection.
Fungal diseases: Mycotoxicosis refers to a group of diseases caused by the effects of toxins produced by fungi/moulds. The major means of flock exposure to mycotoxin is feed but birds can also be exposed to toxins through contaminated litter material. High grain moisture content and poor storage conditions are major predisposing factors.
Several mycotoxins have been identified, and many of them are pathogenic (i.e. are capable of causing disease condition). Mycotoxins rarely act in isolation because moulds have the capacity to produce more than one type of toxin at a particular time thus making their effects additive or synergistic. Because of the immuno-suppressive effects (i.e. reduced ability to combat infections) of mycotoxicosis on birds, exposed flock usually become more prone to other disease agents especially bacterial and viral and also nutritional deficiencies. The disease condition is hard to recognize by an untrained eye. Even professionals must marry post mortem findings with laboratory feed analysis to arrive at a confirmatory diagnosis.
Protozoan diseases: Protozoa are single-celled organisms. They are cosmopolitan in nature i.e. they are found everywhere. Protozoan parasites that are important in poultry production are; coccidia, cryptosporidia, and histomonads.
The most common and economically important of all is coccidiosis. It is caused by Eimeria spp. There are about six species that cause disease in chickens: E. tenella, E. acervulina, E. brunetti, E. maxima, E. mitis, and E. necatrix.
Coccidia organisms infest the lining of the intestine where they multiply massively under a very short period to cause bleeding and erosion of the intestinal lining. The erosion of the intestinal lining reduces its ability to absorb end products of digestion hence affected flock if not attended to promptly will have many birds with stunted growth. It causes high mortality and morbidity. Common signs are weakness, in-appetence, ruffled feathers, weight loss, birds curdling together as in they are cold, brownish/bloody watery diarrhoea, and death if not addressed. Post mortem findings in dead carcass will reveal pale breast muscle, blood stains on the internal surface of the intestine and accumulation of clotted blood in the ceacum depending on the type of Eimeria responsible for the infection. Birds infected with coccidiosis are prone to other infection e.g. necrotic enteritis.
Predisposing factor to coccidiosis are bad management practices like wet litter, overcrowding, high and environmental contamination.