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Progress on the Control of Intestinal Parasites Discussed at AVMA Meeting

17 September 2013

One session at the 150th convention of the American Veterinary Medical Association (AVMA) held in Chicago in July 2013 was devoted to progress in the control of coccidiosis and other intestinal parasites.

Revisiting Lesion Scoring Techniques for Coccidiosis

In 1970, poultry parasitology researchers, J. Johnson and W.M. Reid from the University of Georgia Department of Poultry Science published a lesion scoring method designed to evaluate gross intestinal and cecal lesions induced by single species laboratory infections with Eimeria spp. of chickens, explained Hector M. Cervantes of Phibro Animal Health.

Although the intent of their publication was to standardise lesion scoring techniques among poultry parasitology researchers, veterinarians working for the production and allied poultry industries quickly adopted the technique for routine monitoring of coccidiosis.

However, the current interpretation of the lesion scoring technique developed by Johnson and Reid differs substantially from the original publication. Dr Cervantes highlighted the need to score coccidial lesions more uniformly at the poultry industry level and emphasised the differences between the original publication and its current interpretation.

The Influence of Volume on Coccidiosis Vaccine Uptake in the Hatchery

Successful mass application is critical to the success of any broiler coccidiosis vaccination programme. John E. McCarty, DVM, MAM, from Merial Select stated that all live coccidiosis vaccines require oral ingestion.

A previous study done at the University of Delaware’s Lasher Lab showed that the spray cabinet efficacy is approximately 88 per cent based on oocyst shed rates five to eight days post-hatch. The question remains, can we improve beyond this 88 per cent?

Last year, using the following paper as a starting point (Caldwell et al. (2001) Journal of Applied Poultry Research. 10:107–111), research was implemented to determine if increasing relative photo-intensity at the time of spray application can have a positive impact on vaccine uptake. It did, according to Dr McCarty, so this year, he and his team looked at volume and how it impacted occyst shed based on oocyst per gram of faeces. The findings from these studies and field data were presented at the AVMA Convention.

Protection against Coccidiosis using Eimeria Oocysts suspended in Gelatin Beads

Current methods of preventing outbreaks of avian coccidiosis involve medication of feed with ionophore drugs or synthetic chemicals or by vaccination of chicks with low doses of Eimeria oocysts in ovo or by spray vaccination just after hatch.

Mark Jenkins reported that data from the USDA-ARS Animal Parasitic Diseases Laboratory, Barc in Beltsville indicates that the uniformity and efficiency of vaccination can be improved such that each chick receives a dose of Eimeria oocysts sufficient to induce immunity during early grow-out.

Their battery pen studies have shown that applying gel beads containing Eimeria oocysts to starter feed increases vaccine coverage, equivalent to oral gavage of individual chicks.

In the study presented to the AVMA, day-old chicks were placed in floor pens after being immunised with a mixture of Eimeria oocysts delivered by a different vaccination method (oral gavage, spray vaccination or gel beads). At four weeks of age, chickens (and non-immunised controls) were challenged with a high dose of Eimeria oocysts.

Chicks vaccinated by either gel bead or oral gavage displayed complete protection (P<0.05) against challenge compared to controls as measured by weight gain over the infection period. Chicks immunized by spray administration showed no significant (P>0.05) weight gain protection.

No significant difference (P>0.05) was observed in feed conversion between groups vaccinated by any of the oocyst delivery methods.

Dr Jenkins concluded the findings indicate that gel bead technology is a viable alternative for administering Eimeria oocysts to day-old broiler chicks under poultry house conditions that allow for cycling of oocysts from litter. He added that more practical delivery methods of spraying gel beads onto feed are being explored.

Effect of Lasalocid or Salinomycin on Performance and Immunity Following Coccidia Vaccination of Commercial Broilers

Coccidia vaccines and ionophores have each traditionally been used to control coccidiosis in broilers. More recently, said Kalen Cookson of Zoetis, producers have tried combinations of the two strategies. The goal of their study was to measure the effect of lasalocid (Avatec®) or salinomycin (Bio-Cox®) on oocyst immunity and performance in vaccinated broilers.

Broilers were vaccinated in ovo with Inovocox® EM1 and assigned in a random block design (seven replicates each) to one of seven treatments: no anticoccidial or either lasalocid (LAS) or salinomycin (SAL) in grower feed (G=18-35 days), finisher feed (F=35-50 days) or both (G+F). LAS and SAL were included at 68g per ton and 40g per ton, respectively.

At 36 days, five birds from each pen and 35 non-vaccinated controls were orally gavaged with E. acervulina, E. maxima and E. tenella oocysts. Lesion scores were assessed at 42 days. Birds and feed were weighed by pen at 35, 50 and 60 days.

LAS and SAL groups were significantly protected from challenge against all three Eimeria spp. and 35-day feed conversion ratios (FCRs) were significantly lower (by four to five points, respectively) than EM-1 controls. At 50 days, FCRs of LAS or SAL (G+F) groups were three points lower (not significant). At 60 days, LAS or SAL (G+F) groups had significantly lower FCRs (five to six points, respectively) than EM-1 controls.

Recombinant Profilin Subunit Adjuvanted Vaccine against Avian Coccidiosis Confers Protection against Eimeria acervulina, E. tenella and E. maxima

Montanide ISA 71 VG (ISA 71) water-in-oil adjuvant has been developed to increase cell-mediated immunity and has been selected previously to be used in conjunction with profilin as a candidate vaccine for in vivo coccidiosis protection. In this paper, Heloise Imbault of SEPPIC Inc. showed that subcutaneous vaccination of chickens with E. acervulina profilin and ISA 71 induces cross-protection against infection with E. acervulina, E. maxima and E. tenella.

Vaccination with profilin/ISA 71 was associated with greater body weight gain following E. acervulina and E. maxima infections, and decreased parasite faecal shedding after E. acervulina, E. maxima and E. tenella infection, compared with non-vaccinated birds. Anti-profilin antibody levels were higher in sera of chickens vaccinated with profilin/ISA 71 than with profilin alone.

Finally, the levels of transcripts encoding interferon-γ, interleukin (IL)-2, IL-10 and IL-17A were increased in intestinal lymphocytes from chickens infected with E. acervulina, E. maxima or E. tenella and vaccinated with profilin/ISA 71 than with profilin alone.

None of these effects was seen in chickens injected with ISA 71 alone, indicating that the adjuvant did not confer non-specific immune stimulation.

In this study, Dr Imbault said that, using comparative RNA microarray hybridisations, it was shown that transcripts levels are altered in a larger number of biological functions in birds vaccinated with ISA 71 adjuvanted profilin than with profilin alone, compared to profilin adjuvanted with a reference water in oil adjuvant dedicated to antibody production (Montanide ISA 70 VG) versus profilin alone.

These results suggest that profilin plus ISA 71 augments protective immunity against selective Eimeria species in chickens.

Comparison of the Susceptibility to Eimeria Maxima in Different Commercial Lines of Broiler Chickens

Coccidiosis is a very costly disease to the poultry industry. The two main modes of disease control over the years have been in-feed anticoccidials and vaccination. The current expense for preventive medication exceeds $90 million in the United States and more than $300 million worldwide (McDougald, 2008). Even though the cost of preventative medications are high, according to Chad M. Malinak of the University of Georgia, the selection of viable options is diminishing due to the high cost of producing new medications, anticoccidial resistant strains and changing consumer preference.

There have been studies to show that there can be differences in susceptibility between inbred lines of layers (Bumstead, 1987). Significant changes in the growth rate and feed efficiency in broiler chickens have resulted in the decreasing age at slaughter every year.

The objective of the Georgia study was to evaluate whether there is a difference in resistance or susceptibility to Eimeria maxima in four commercial broiler chicken lines. E. maxima were selected for this study for the influence it has as a risk factor for the onset of necrotic enteritis.

Broilers were inoculated with pure E. maxima strains and the following parameters were then evaluated in each group: mortality, plasma carotenoids, feed conversion, average daily weight gain, lesion scores (using Johnson and Reid) and faecal oocyst output by microscopy.

Impact of Coccidiosis Vaccination Growth Curve on Live Bird Body Composition and Flock Uniformity

Broilers vaccinated with a live coccidiosis vaccine exhibit a different coccidiosis challenge and growth pattern from broilers fed an in-feed ionophore programme, according to Linnea J. Newman, Robert G. Teeter and Stephen W. Davis from Merck Animal Health.

In the case of the vaccinated broiler, the immunity-building process may cause some depression of daily gain at some point during the time period between 14 and 24 days, followed by compensatory gain.

Studies were designed to see if the compensatory gain period following immunity in vaccinated flocks provides an opportunity to alter live bird body composition through ration formulation.

Proximate analysis of whole bird body composition, including protein, fat, ash, water and energy via DEXA scan of birds fed four dietary energy levels in a controlled pen study provide data on live bird yield and is correlated to bird performance through the entire growth curve. Coccidiosis-vaccinated commercial broiler flocks provide data on carcass uniformity and yield in applied experiments under commercial field conditions.

Early coccidiosis immunity, and ration formulation adjusted to the coccidiosis vaccination growth curve provide an opportunity for significant production cost savings, the researchers concluded.

Incidence of Intestinal Worms in Broiler Breeders in the US

The objective of a study presented by Sara J. Steinlage of Elanco was to get a representative sampling of the degree of helminthiasis in broiler breeder operations in the US.

With these data, the incidence and severity of the infections could be determined in various complexes, companies and perhaps the industry. In addition, an effort was made to compare the “quality” of the farm with the incidence of helminthes.

Intestinal samples were collected from 10 companies representing 15 different complexes throughout the US for a total of 281 intestinal tracts.

Helminths isolated and identified in the intestinal tracts (and overall incidences) were Heterakis gallinarum (96 per cent), Capillaria obsignata (75 per cent), Ascaridia galli (63 per cent) and Raillietina cesticillus (14 per cent).

Dr Steinlage added that, although the difference between good and poor performing farms was not statistical, there was a trend for the poor performing farms to also have a greater worm burden.

Broiler Breeder and Pullet Intestinal Worm Incidence in Field Post-mortems

The presentation by Francene Van Sambeek of Elanco summarised 13 months of field reports on the incidence of round worms, caecal worms, tapeworms and capillary worms in broiler breeders and pullets.

Further Reading

Find out more information on coccidiosis by clicking here.

September 2013

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