Poultry Diseases Up Close – Coccidiosis

The excellent Keeping Chickens has made an excellent video which gives an overview of coccidiosis in chickens and shows how devastating just one bird with coccidiosis can be to an unprotected flock. While coccidiosis can occur at any age the greatest danger of infection is in chicks from four to eight weeks old. It takes around 6 days for the disease to run its course. Often there are no visible symptoms until the third and fourth days. This video does include some archival footage of chicks with coccidiosis and shows some of the symptoms of the disease as it progresses which may be upsetting to some.

Coccidiosis (pronounced coc·cid·i·o·sis) is one of the more common and costly diseases in poultry.  Chicken keepers in the past had come to accept a loss of 10 – 20 birds per hundred and the stunting of eight to ten more as a normal cost of doing business.  While coccidiosis can occur at any age, the greatest danger of infection is in birds of four to eight weeks old.  It is generally accepted that all young birds reared on litter are exposed to this costly disease.”

“Coccidiosis is caused by microscopic parasite in a tiny egg-like cell, which is protected by a very tough covering.  This cell, known as an oocysts is passed in the droppings, in this stage it is non-infective, but after about two days of moisture and warmth, significant changes begin to take place in the non-infective oocysts.  Four spores develop, each with two banana shaped spore zoites, so that each oocysts, when matured, contains eight spore zoites.  The oocysts is now know as an infective oocysts.

When it is swallowed by a chick the infective oocysts passes down the warm, moist intestinal tract, where the digestive juices of the bird dissolve the hard protective covering of the oocysts.  The spores break through the weakened wall of the oocysts and then the spore zoites escape from the spores.  These released organisms invade the cell lining the ceaca or other parts of the intestine, depending on the species of parasite.  Once inside the cell wall, the spore zoite develops into a rounded body enclosing the nucleus.  This nucleus slipts into two nuclei.  These in turn split and the process repeats until growth stops and a considerable number of nuclei have developed.  Then around each nucleus a new organism called a merozoite forms, fitting with the others into a clump resembling the segments of an orange.”

“It takes about six days for the disease to run it’s course.  Often there are no visible symptoms until the third and fourth days, when the merozoites break through the cell walls and cause the ceca to fill with blood and to swell considerably.  By the fourth day the chick has become listless and begins to show the typical ruffling of the feathers and failing appetite.  During this stage birds may begin to die from loss of blood, but it is the fifth day when the greatest number of deaths occur.  Blood begins to appear in the droppings and the second generation of organisms invades many more cells.  Some of the birds still die in the sixth day, but those that survive the attack are immune and begin to improve.  The blood in the ceca starts clotting which in turn causes shrinking.  The colour of the walls of the ceca begin to return to normal.  later on the sixth day the oocysts begin to pass in the droppings.”

“When we realise that one parent cell is capable of producing over 500,000 oocysts, it’s not difficult to understand how an entire flock may be infected by one single diseased bird.  Under farm conditions the birds pick up the infected oocysts from such places as the litter, yards, dirty feeders and waterers to spread the disease.  To aid in the prevention of coccidiosis, there are medicated chick feeds.  An alternative to medicated feed is to have your chick vaccinated.  If a breakout does occur, the cushioning effect of the preventative medication will keep the deaths and stunting loss to a very small percentage compared to birds not protected with the preventative medication.  As effective as these medications are, they cannot replace good management and sanitation practices.  To minimize the chance of a breakout, flocks should not be overcrowded, litter should be kept dry and their area always well ventilated.”

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