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Dr. John McCarty

Dr. John McCarty, Senior Veterinarian, Merial, Inc.

Dr. John McCarty has prepared a practical article dealing with control of coccidiosis in broiler growing with reference to winter conditions. Successful application of vaccines requires appropriate administration and structured monitoring as described.

Coccidiosis can have an enormous impact on broiler performance which is most often reflected in reduced weight gain and decreased feed efficiency. It is considered to be the most costly pathogen challenge in modern broiler production in the U.S. While coccidiosis is a year-round problem, cold weather conditions can result in changes in the ecology in a broiler house that lead to increased cocci challenge.

When the weather cools and the houses tighten up, disease challenge tends to increase in the chicken house. As ventilation is decreased to help conserve heat, more moisture remains in the house. The increased moisture, especially in the litter, favors increased bacterial, viral, and cocci load.

Coccidia need moisture and heat for the oocysts to sporulate. Once these are sporulated, oocysts become infective to the chicken. The increase in moisture can lead to greater sporulation of the oocyst population. And, as more of the oocysts sporulate, birds are faced with a heavier cocci challenge.

The use of coccidiosis vaccines can help influence the nature of the load. Continued use of vaccines helps dilute the wild cocci population with a vaccine strain. In particular, vaccines with precocious strains place minimal stress on the bird while at the same time providing adequate stimulation for immunity development, and the bird can be protected with less stress.

The nature of the precocious strain vaccines allows for the increase of sporulation to be less detrimental, since the number of oocysts shed are less when compared to non-precocious strains of cocci. Even though there are fewer numbers of oocyst with the precocious strains of vaccine, the number present is still more than adequate to stimulate proper and complete immunity.

Coccidiosis control also helps minimize disease challenge from other organisms. A critical one when it comes to gut health is clostridia. Disruption of the intestinal lining, such 

as that caused by coccidiosis, provides opportunity for clostridial organisms to infect the gut and to cause disease such as necrotic enteritis. By reducing the level of coccidiosis, less disruption in the gut provides less opportunity for clostridial infection. This would also help the bird regarding nonspecific enteritis, both clinical and subclinical.

Sporulating Oocysts require heat
and moisture to develop in litter

There are many ways to prepare for the cooler months, but assuring proper cocci control prior to the onset of cold weather will keep a low cocci load in the house. Then, the use of a precocious vaccine strain during these months of the year allows for minimal stress on the bird’s digestive system while still providing optimum immunity against cocci.

It will also be important to continually monitor the cocci challenge. Doing routine postings of broilers to assure there is proper cycling helps confirm that the vaccine is doing its job of developing proper immunity.