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Trends and research affecting coccidiosis management

Producing meat without antibiotics and other drugs has long been advocated by European consumers and regulators and it appears that more Americans are following suit.

Consider the following preliminary findings from the 2006 Manufacturer Survey of the Organic Trade Association (OTA), a US organization reporting on US food trends:

• Organic food sales totaled nearly $14 billion in 2005, representing 2.5% of all retail sales for food.
  
  
• Organic food sales are expected to reach nearly $16 billion by the end of 2006.
  
  
• The fastest-growing organic food in 2005 was organic meat, including poultry, with sales rising by over 55%.
  
  

"These findings show there is continued strong growth for organic products, which means additional opportunities for farmers and more choices for consumers," according to Caren Wilcox, the OTA's executive director.

The OTA has also forecasted that the fastest growing category of organic product sales would be poultry with an anticipated average annual growth of over 33% through 2008.

To meet this demand, many mainstream poultry operations in the Americas and Europe have already discontinued their use of growth-promoting antibiotics "either voluntarily or because of legislation "and are placing more emphasis on intestinal health programs as a means of controlling disease. Vaccination control has also helped operations reduce or discontinue the use of chemicals or ionophores for coccidiosis control.

Editor's note: The following news items are from the IX International Coccidiosis Conference in Iguasu Falls, Brazil.

Late production E. maxima problems linked to anticoccidial resistance

Problems with Eimeria maxima infections late in the production cycle appear to be linked to extensive use of ionophore antibiotics and resulting ionophore-resistant E. acervulina, says Dr. Greg F. Mathis of Southern Poultry Research, Inc.

An earlier study suggested that E. acervulina can interfere with E. maxima colonization. Consequently, Dr. Mathis designed a battery cage study to examine the relationship of E. acervulina sensitivity to the ionophore salinomycin and subsequent infection levels with E. maxima.

Birds were fed nonmedicated feed or salinomycin at the rate of 60 grams/ton and were then challenged with either a salinomycin sensitive strain of E. acervulina, a resistant strain of E. acervulina and/or an E. maxima field isolate.

The oocyst per bird challenge levels were as follows:

• None (control)
  
  
• E. acervulina (sensitive strain) 50,000
  
  
• E. acervulina (resistant strain) 50,000
  
  
• E. acervulina (sensitive strain ) 50,000 plus E. maxima 5,000
  
  
• E. acervulina (resistant strain) 50,000 plus E. maxima 5,000
  
  
• E. maxima 5,000
  
  

E. maxima alone caused a 20% weight reduction and 2.70 lesion score, said Mathis.

Salinomycin controlled the sensitive strain with 5% weight reduction and 1.25 lesion score. It did not control the resistant strain, resulting in a 22% weight reduction and 2.75 lesion score.

Birds infected with E. maxima and the sensitive E. acervulina strain had E. maxima lesion scores of 2.25. The birds infected with E. maxima and the resistant E. acervulina strain had E. maxima lesion scores of 1.30.

"From the results it can be inferred that E. acervulina interfered with development of E. maxima. Higher anticoccidial resistance allows more E. acervulina colonization, which appears to interfere with colonization of E. maxima, and thus indirectly slows E. maxima immunity development.

"This increases the chance for late problems with E. maxima, possibly explaining an increase in field reports of late E. maxima infections where salinomycin has been extensively used," Mathis said.

Lesser known Eimeria species underestimated

Two lesser-known Eimeria species in poultry may be underestimated in importance.

One of the species is Eimeria mitis. "Mitis" means mild and the species is so named because it has been considered to be of minor significance in poultry, said Dr. Luciano Gobbi, of Schering-Plough Animal Health, Italy.

However, a two-phase trial has shown that, in contrast to its name, E. mitis can impair chicken performance and cause losses just like other, better known Eimeria species, the veterinarian said.

In the first phase of the study, groups of 14-day-old Ross 508 chickens were infected with either E. mitis or Eimeria acervulina, a species of coccidia known to have a significant adverse effect on chickens. A third group of birds received saline solution and served as a control. The success of the challenge was confirmed by oocyst counting and shedding. Bird performance was evaluated.

Compared to controls, birds that received either E. mitis or E. acervulina had significantly lower daily weight gain, feed intake and water consumption, as well as a higher feed conversion ratio and lower final body weight, Gobbi said.

In the second trial phase, three additional groups of 14- day-old Ross 508 birds were challenged with E. mitis and E. acervulina and were then injected with Pontamine Sky Blue dye to enable evaluation of intestinal mucosa, he said.

Eimeria-infected chickens exhibited color differences in the mucosal surface compared to controls. In fact, only the infected birds had dye leakage between 72 and 144 hours post-infection. The leakage stained intestinal mucosa and gut contents, confirming cell damage and increased gut permeability due to the multiplication of both Eimeria species. In addition, infection with either Eimeria species caused significant gut wall thickening due to edema and inflammation, he said.

"The results indicate that E. mitis can impair chicken performance and cause losses just like other, well-known Eimeria species, despite the name E. mitis," Dr. Gobbi said. Dr. Steve H. Fitz-Coy, also of Schering-Plough Animal Health, reported on E. mivati, a coccidial species that some researchers have considered to be a variant of E. acervulina or a mixture of E. acervulina and E. mitis, but not a unique species.

Fitz-Coy identified several field isolates from Georgia and the DelMarVa Peninsula that fit descriptions of E. mivati. He selected three of the isolates and sent them with 10 other Eimeria species samples to an independent lab for polymerase chain reaction (PCR) assay. The identity of each sample was not known by the lab.

"The only isolates that could not be identified by PCR assay were the E. mivati samples," he said. The current primers for identification of Eimeria species include E. acervulina and virtually all the other Eimeria species known to affect chickens "except E. mivati, Fitz-Coy said. The PCR test indicates that E. mivati is, in fact, a valid and unique Eimeria species, he said.

E. mivati is also "moderately pathogenic" in chickens and, on some occasions, can cause mortality, according to Fitz-Coy. In one study, mortality due to E. mivati was 40% in naive chickens, but there was no pathology in hyperimmunized hatch-mates.

Water potential carrier of coccidia to poultry

Drinking water may be a potential carrier of coccidia to chickens, according to a new study.

The study focused on 24 farms that used forage or surface water and did not include farms supplied by treated water, said Reperant Jean-Michael, Le Du Maryse, of the French Agency for Food Safety, Zoopôle Les Croix, Ploufragan, France.

Fecal samples from the farms showed that 75% of the flocks were positive for coccidia. When filters were placed to capture oocysts where water entered the buildings, four of the samples were positive for coccidia, he said. The species of coccidia found in the water was Eimeria acervulina, which was also present in litter from farms in the study, the investigator said.

"These preliminary results suggest that water can be a potential carrier of coccidia for chickens," he said, adding that other forms of water supply could be considered in future studies.

Source: CocciForum Issue No.12, Schering-Plough Animal Health.