Coccidiosis has been one of the costliest health threats throughout the several decades that the modern poultry production industry has existed, and over the years, a variety of different control options have been developed, from synthetic “chemical” coccidiostats, to ionophores, to vaccines.
According to Elanco, however, there are important distinctions between these different categories that must be kept in mind in order to ensure animals remain as healthy as possible, lowering the environmental footprint of production. Today, we hear from Dr. Tom Jeffers, adjunct professor of animal science at Cornell University, about how these products work and how resistance to them is unlikely to be developed. He is joined by Philippe Gelaude, Elanco’s poultry technical consultant for Belgium & the Nordic countries, and Dr. Emily Kimminau, Elanco’s US poultry technical advisor, who share data from both trials and field experience about how different coccidiosis control programs have performed in Europe and America.
[Feedinfo] What are some of the considerations when deciding whether to use ionophores or vaccines to control coccidiosis?
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[Tom Jeffers] There are several things to consider in the use of vaccines to control coccidiosis. Much of the concern stems from the fact that all coccidiosis vaccines contain live oocysts of coccidia that, when ingested by the broiler, result in a coccidiosis infection. An initial concern is the lack of uniformity of exposure to vaccine oocysts when the broiler chicks are first administered the vaccine. Some of the chicks ingest too many oocysts, while some consume none and thus go to the grow out facility without an immunological priming exposure to the immunizing antigens of the coccidia. This concern is compounded by the fact that such infections must proceed to the damaging schizont stage of the coccidia lifecycle to elicit immunity, because only the merozoites of coccidia are immunogenic. Such vaccine-induced infections are, therefore, a threat to intestinal integrity and are a precursor to necrotic enteritis. A further disadvantage in the use of coccidiosis vaccines is the fact that all the species of coccidia, except for Eimeria maxima, must produce multiple infections to elicit protective immunity, meaning that vaccinated broilers may face the threat of coccidiosis throughout their life, right up until processing. |
Dr. Tom Jeffers |
None of these disadvantages must be considered in the use of an ionophore to control coccidiosis. In fact, the use of an ionophore provides the perfect balance between the coccidia and the broiler, in that the ionophore prevents clinical coccidiosis while allowing a low level of cycling of the coccidia, thus allowing immunity to develop in the absence of clinical coccidiosis while being medicated with the ionophore. This assures the maintenance of intestinal integrity and prevents coccidiosis from being a precursor to necrotic enteritis. Therefore, when deciding to use ionophores or vaccines to control coccidiosis, there are clear advantages in using an ionophore.
[Feedinfo] You have overseen trials comparing flocks treated with ionophores versus those receiving coccidiosis vaccines. Can you briefly introduce these trials? What differences did you observe in the health and performance of the different flocks?
[Philippe Gelaude] In a recent French study different coccidiosis prevention strategies were indeed compared to each other, including commercially available coccidiostats and a coccidiosis vaccine consisting of 5 different strains. This pen trial focused on differences related to intestinal integrity and performance between both treatment groups.
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While the first treatment group was vaccinated against coccidiosis in the hatchery, the second received a narasin based anticoccidial program (Maxiban® until day 27 followed by Monteban® until slaughter). Both groups were inoculated with sporulated oocysts at day 21 and Elanco’s Health Tracking System (HTSi) was used at day 27 to collect health data in a standardized manner. In total, 23 intestinal lesions were evaluated, including coccidial lesion scores, in order to generate the Intestinal Integrity (I²) Index, which also has a proven direct correlation with performance data such as Feed Conversion Rate (FCR) and Average Daily Gain (ADG). It is generally accepted that I² below 90 is considered as suboptimal. |
Philippe Gelaude |
Differences related to intestinal health and performance were quite clear between both treatment groups. While the narasin-based anticoccidial program resulted in 95.8% of birds without E. acervulina lesions and only 4.2% with score 1 lesions, 41.7% of the vaccinated birds had a score 2 or higher, resulting in a suboptimal I² score below 90 for the vaccinated group. The Maxiban®/Monteban® treatment group had a significantly higher intestinal integrity (I²) of at least +6 points resulting in an increase of ADG (+1.23g/day), body weight (+60g) and carcass yield (+0.7%) combined with a reduction of FCR (-4.5 points) compared to the vaccinated group.
[Feedinfo] What role do coccidiosis vaccines play in broiler production in Europe, and what can real world data like those from HTSi tell us about the differences between ionophores and a vaccine program?
[Philippe Gelaude] Coccidiosis vaccines have a place within the toolbox of coccidiosis prevention in the poultry industry and especially within the laying bird segment; however, ionophore based programs remain the number one choice in broilers. While scientific studies have already highlighted the animal health and performance benefits between both coccidiosis prevention strategies in controlled environments, these findings are also supported by field data collected through Elanco’s Health Tracking System (HTSi). The HTSi database has already proven that it can be used to inform and evaluate changes that can optimize intestinal health, and hence welfare, productivity, and sustainability of the poultry industry. Therefore, the database of three European countries has been consulted to investigate if ionophore-based programs result in higher bodyweights and higher flock uniformity compared to vaccinated flocks. More than 1000 vaccinated birds and approximately 4900 birds which were treated with ionophores were included. When controlling for bird age and geography, broilers belonging to the ionophore group had a significant higher uniformity and bodyweight (+64,1g) compared to vaccinated birds. Later field data supports the findings of the aforementioned scientific studies.
At the same time, HTSi is a valuable tool since it has the possibility to answer new questions that arise in a continuously evolving European broiler industry. Since the broiler industry is changing in Europe, with the rise of slow growers in areas such as the Netherlands, it must be taken into account that this might impact coccidiosis prevalence of several Eimeria species and the evolution of coccidial pressure within the poultry house. Based on HTSi data, E. acervulina, E. maxima and E. tenella are still the most dominant species present in Dutch slow growers, while E. necatrix and E. brunetti have also been detected and thus pose a risk in this type of broiler production. While the use of anticoccidials in broilers such as ionophores result in a broad protection against Eimeria spp., higher flock uniformity and higher body weight, vaccination will only confer a certain amount of protection against the Eimeria spp. included in the vaccine.
[Feedinfo] Beyond the health and performance impacts, the decision of what sort of coccidiosis control tool to use is also influenced by regulatory and market concerns. For example, in the US, ionophores are technically classed as an antibiotic. What were the experiences of US producers seeking to move away from the use of ionophores as part of a larger No Antibiotics Ever (NAE) push?
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[Emily Kimminau] Ionophores have been fundamental in coccidiosis control in the US since they were released to market. Their removal resulted in a drastic shift in coccidiosis control programs. There were also more challenges with other diseases often associated with coccidiosis, namely Necrotic Enteritis (NE). This led to increased mortality in addition to decreased performance. Producers also saw increased cost of production. Although the chemical anticoccidials provide protection against coccidia, they do not impact Clostridium perfringens, the causative agent of NE. Therefore, producers had to find alternative products. While some had success, there was no “silver bullet”, and in many cases, it required producers to utilize multiple products, ultimately increasing costs. In some instances, water products were used to help mitigate NE losses, but because of the great farm to farm variation, adequate application is much harder to ensure when compared with in feed products. Also, because so many producers shifted to NAE relatively quickly, the market was flooded with these birds, and therefore very few got a premium for the product. |
Dr. Emily Kimminau |
[Feedinfo] And how is the thinking on antibiotic-free poultry production evolving as a result of that experience? Why is NAIHM (No Antibiotics Important in Human Medicine) now being considered rather than NAE and what does this mean in terms of coccidiosis control?
[Emily Kimminau] Coccidiosis continues to be the most prevalent challenge and financial burden on poultry producers around the world. As long as birds are raised indoors, we will continue to create the perfect environment for coccidia infection. Taking away a beneficial tool to help with coccidia-associated losses was a difficult move in the United States. It put pressure on the already limited available control measures. We are not likely to see another coccidia drug come to market, so it is crucial to utilize what we have and reduce the risk of resistance. While some US companies stood by the removal of ionophores, others such as McDonald’s understand the limited options you leave producers with to control coccidiosis – and that control of coccidiosis is critical for bird performance, welfare and decreasing the carbon footprint. At the end of the day, ionophores are not used in human medicine, and so should continue to be utilized as an important tool for maintaining health and providing affordable poultry for consumers worldwide.
[Feedinfo] One final concern about widespread use of any antimicrobial substance is the likelihood of the target microbe acquiring resistance, making the drug less effective. To what extent is this a concern for ionophores and what have we learnt in the last 5 decades on achieving stable and sustainable cocci control?
[Tom Jeffers] When considering the potential for anticoccidial drug resistance, we must recognize that coccidia are sexually reproducing organisms and thus genetic traits in the coccidia follow Mendelian rules of inheritance, unlike some microbes in which resistance can be transferred to other microbes through cytoplasmic inclusion bodies such as plasmids. Coccidia do not have such cytoplasmic inclusions and their genetic traits are conferred through the expression of genes on one or more of their several chromosomes. Thus, the sporulation process of the oocysts of coccidia results in eight sporozoites, the invasive stage of the coccidia, with one set of four sporozoites being genetically identical, while the other set of four sporozoites, although genetically distinct from the other set of four, are again genetically identical with each other.
Moreover, the likelihood of anticoccidial drug resistance is directly related to the complexity of the mode of action of the respective anticoccidial. A relatively simple mode of action requires a relatively simple genetic change, or mutation, within the coccidia to circumvent the action of the anticoccidial through the development of resistance. The synthetic anticoccidials, now often referred to as “chemicals”, all have a relatively simple mode of action, often blocking a critical biochemical pathway in the metabolism of the coccidia that is essential to their survival. As an example, we may take the synthetic anticoccidial decoquinate. It blocks cytochrome, an enzyme in the mitochondria of coccidia essential to mitochondrial respiration, thus preventing the asexual stages of the coccidia to divide and form schizonts containing multiple merozoites. This anticoccidial effect can be overcome with a single gene mutation in the coccidia, allowing them to circumvent the blockage of mitochondrial respiration and to go on to divide and reproduce normally. Thus, resistance can develop in a single generation of coccidia and result in the failure of decoquinate to control coccidiosis in medicated broilers very rapidly after initial use in the broiler ration. Since each oocyst would contain four sporozoites carrying the resistance mutation, one can see how resistant coccidia could quickly dominate the population of coccidia in the broiler grow out facility.
By way of contrast, ionophores have a very complex mode of action. They become incorporated in the bilipid membrane surrounding the sporozoite. Once there, they transport cations such as sodium into the sporozoite, quickly resulting in an osmotic imbalance within the sporozoite. The sporozoite, in turn, tries to eliminate this excess of sodium ions by pumping the sodium out using an enzyme, sodium/potassium ATPase. This requires energy that the sporozoite was going to use to invade an epithelial cell in the intestine of the broiler and initiate an infection. The sporozoite then quickly runs out of energy, resulting in a lethal osmotic imbalance in the sporozoite and robbing it of the ability to invade an epithelial cell in the intestinal lumen of the broiler. To overcome this complex anticoccidial action of the ionophore would require several genetic changes in the coccidia and likely would require the linkage these mutations across several chromosomes of the coccidia. As a result, the coccidia have not been able to accomplish such a complex genetic adaptation to the ionophores and resistance to this class of anticoccidials has not been a problem.
Perhaps the very best evidence of the lack of resistance to the ionophores, resulting in their continuing effectiveness as anticoccidials, is the growth performance of modern-day broiler chickens while medicated with an ionophore. By using the ionophores to protect against coccidiosis over the last 5 decades, many global broiler producers are achieving growth and feed efficiency in their broiler flocks approaching the genetic potential of their broiler chickens.
Published in association with Elanco
