Special sessions were dedicated to coccidiosis control during the Poultry Science Association Annual Meeting held in St Louis, USA in July 2011.

Practical Aspects of Coccidiosis

Dr Linnea Newman, from Merck Animal Health, stated that a quarter of a century ago, broiler coccidiosis control using in-feed anticoccidial medication was highly effective. Rotation and shuttle programmes maximised efficacy, and control could be maintained with minimum flock-to-flock variation regardless of environmental conditions.

But as sensitivity of the field coccidia decline, we must accept that farms will be subjected to some degree of Eimeria challenge or "coccidiasis" during the life of the flock.

"Control" used to be the word that was used. The reduced efficacy of the anticoccidials and the loss of 3-nitro make "management" a more appropriate word, she said.

The genetics of the modern high-yield broiler allow slaughter by 30 to 36 days in many markets, and slaughter age will often coincide with the peak of Eimeria challenge.

Coccidiosis or coccidiasis is no longer just a disease of a single bird or a single flock. It is a dynamic population that produces different clinical or economic outcomes depending upon many field factors such as stocking density, environmental humidity, slaughter age and the influence of the coccidiosis control program of the previous flock.

Sporulation is necessary for the oocysts and heat and moisture is needed for sporulation. Moisture comes from faeces. Low density, small chicks, equals little poop while high density – big birds, full house – equals more poop. Coccidiosis multiplication increases with increased moisture.

Lower density means immunity takes longer. Higher density means it breaks quicker and immunity develops quicker, said Dr Newman. Lower density makes it harder to measure coccidiosis, but it is there. It takes longer and immunity develops eventually; that is the natural way coccidiosis interacts.

Anticoccidial programme as a factor

Dr Newman stated that effective chemicals severely depress coccidiosis reproduction. When they stop working, there tends to be a break. Ionophores allow a bit of leakage.

Eimeria reproduction is slowed by in-feed anticoccidial medication, low stocking density and low environmental humidity. This results in populations that peak at 28 days of age or later. When this peak corresponds to the final two weeks before slaughter, negative economic impact is maximized.

In Europe, where they use clean litter after each flock, there is a coccidiosis challenge early. In the US, they reuse the litter (not changed after each flock), and the coccidiosis challenge comes late.

In Europe, there is full ionophore use and high density while in the US chemicals rather than ionophores are used, with lower house densities. The timing of the lesion can significantly impact performance.

Dr Newman emphasised one more important concept: carry-over. Bird slaughter at peak shedding presents early challenges in the next flock, whether one has clean litter or reused litter. This is really important, she said.

A peak in Eimeria shedding immediately before slaughter appears to result in the carry-over of a higher challenge to the subsequent flock, even when cleaning and disinfection are employed.

She said: "It carries over whether you clean out or not. We can't get it out, no matter what we do. This increases need for starting anticoccidials in the next flock.

"This gives a greater opportunity to create immunity. But, if you let it get bad at the end of the life of one flock, the worse it is on the next flock," she said.

A peak in Eimeria shedding immediately before slaughter appears to result in the carry-over of a higher challenge to the subsequent flock, even when cleaning and disinfection are employed.

This early challenge may alter the clinical and economic outcome of the Eimeria population dynamics in that flock, which may, in turn, influence the next flock in sequence.

When you have a dry environment, low stocking density, clean litter and whole house brooding, good things happen, Dr Newman concluded.

Worldwide Perspective

Dr Martin S. De Gussem from Vetworks in Belgium said that coccidiosis in poultry is still considered one of the main diseases affecting performance of poultry reared under intensive production systems. With current available diagnostic methods such as oocyst counts and lesion scoring, a good interpretation of the impact of subclinical coccidiosis is not easy.

Another problem which is difficult to address is the interpretation of the efficacy of an anticoccidial programme. Anticoccidial sensitivity testing of the different drugs available is the only reproducible method available today but interpretation is far from easy.

The result of all this is that coccidiosis is underestimated as a health hazard and thus remains an important economic threat. Continuous optimisation of anticoccidial programmes is advantageous to the broiler industry, he said.

In addition to this, a link between subclinical coccidiosis and bacterial enteritis complicates choosing the right tools and strategy for poultry producers, particularly in countries producing poultry meat without growth promoters and/or with vegetable diets only.

Bacterial enteritis is an issue in Europe and Latin America, although those regions do not have problems with necrotic enteritis.

Implementing sound shuttle and rotation programs, making use of all available and validated preventive tools (anticoccidials and live vaccines) is essential to not only control clinical, but mainly subclinical coccidiosis.

While basic rules for preventive programs are applicable all over the globe, there are regional differences, such as: poultry meat organoleptic requirements, legislation in and availability of anticoccidial drugs and vaccines, management and impact of climatic conditions on coccidiosis challenge. Anticoccidial prevention programs are per definition tailor made and solutions should continuously be evaluated.

He said that subclinical coccidiosis in Europe causes a nine per cent production loss. The subclinical disease is difficult to diagnose, prevent and correct.

Coccidiosis diagnosis

Dr De Gussem discussed the different diagnostic tools used with coccidiosis.

• Oocyst per gram (OPG) (faeces in the litter) counts are used in Europe but are not used that much elsewhere. They are labour-intensive and expensive. There is a poor relation between OPG and performance.
• Coccimorph is a computer method of diagnosis. It was developed in Brazil and uses photographs.
• Anticoccidial Standard Testing (AST) is not used that much.
• Lesion Scoring (LS) is done all over the world. It scores macroscopic lesions in the gut (from 0-4). It is labour-intensive, expensive and difficult to do, with sometimes confusing, and sometimes subjective results.

However, LS has a very strong relation with performance. Several time-points are needed to get accurate results. Companies need to establish their own data per complex/integration. Large producers need to compare coccidiosis levels. It is very important to figure out the differences between complexes. Producers must carry out bench-marking.

To conclude, Dr De Gussem said that subclinical coccidiosis remains an important problem in the international poultry sector.

Coccidiosis Effects on Energy Costs

Dr Bob Teeter, from Oklahoma State University in the US, evaluated coccidiosis impact and calorific costs. Coccidiosis is one of the most expensive diseases and a major immunity stressor, he said.

Immunity to coccidiosis is variable, taking from two to four weeks to develop immunity for E. maxima.

Dr Teeter and his colleagues carried out a metabolic chamber experiment in which two groups of birds were reared in coccidiosis-free environments with one vaccinated at hatch and the other maintained as naïive to cocci.

There were five challenge periods which consisted of an oral dose of sterile saline or a mixture of three Eimeria species administered as oocysts to naive birds at 14, 21, 28, 35, and 42 days.

Though coccidiosis challenge occurring early in the production cycle had an energy cost, birds exposed late (at 35 to 42 days) exhibited higher costs.

The Effective Caloric Value (ECV) system rearranges the way we look at caloric density. Increase in caloric density can improve feed conversion: dietary energy, body weight and feed conversion relationships.

Effective caloric value (ECV) places caloric density equivalents upon nutritional and non-nutritional factors. In this study, coccidiosis mediated lesion scores six day post-challenge had a marked deleterious impact upon ECV.

Lesion scores of 1 and 2 reduced the dietary energy value from an initial 3,200kcal per kg ration by 125 and 596kcal for 800-g broilers and by 625 and 2,277kcal per for 3-kg birds, respectively, Dr. Teeter said.

Management issues, nutritional and non-nutritional factors, such as light, housing, stocking density and feed form all have an impact on energy costs. Hygienic challenges reduce nutrient utilisation and the inflammation of intestines reduces absorption. However, lesion score cost far exceeded consequences for inadequate lighting program and poor pellet quality.

In the test they ran, the birds were challenged with 1ml of E. acervulina, E. maxima and E. tenella and at 35 days, energy consumption dropped as the birds got sicker. Feed conversion deteriorated. Average daily gain fell by 25 per cent (70 per cent compared to the controls). Plus, malabsorption got worse.

"Coccidiosis hurt performance, energy and consumption by a huge amount. It is critical not to have late growth challenges. While early challenges had a minor negative effect, late coccidiosis stress had major negative effect on: feed conversion, average daily gain, feed consumption," he said.

Dr. Teeter concluded by saying that when coccidiosis occurs in the final two weeks of the growth cycle, even minor lesions significantly reduce performance.

Further Reading

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Find out more information on coccidiosis by clicking here.

December 2011