One of the biggest challenges in poultry production nowadays is to learn how to raise chickens without antibiotics and coccidiostats. This will automatically result in an increased need to rely on prevention strategies, especially Eimeria vaccines. But are Eimeria vaccines and antibiotic reduction incompatible or can they coexist?
What’s the real cost of Coccidiosis?
Coccidiosis caused by Eimeria parasites is one of the most common and widespread diseases in modern commercial poultry systems.
The global cost of coccidiosis has been recently estimated to be >$3 billion per annum. This cost calculation is based on direct production losses and indirect costs for prevention measures. However, most of this financial loss comes from an increased feed conversion ratio (FCR) and decreased weight gain (Williams, 1999). In addition, clinical disease – in broilers mainly caused by Eimeria tenella – leads to increased mortality. Finally, Eimeria is also one of the most important predisposing factors for bacterial enteritis.
Anticoccidial feed additives or anticoccidial drugs have been and still are the most widely used prevention tool in broilers. These products have many merits but the two main issues associated with their use are (i) reduced sensitivity of Eimeria parasites when a certain product is used for too long or too often and (ii) cross resistance between certain compounds (Marien et al., 2007).
The need for prevention against this disease is as old as coccidiosis itself in poultry farming. It has been some time since the first vaccines were developed and fortunately innovations have been incorporated into the production process which have meant that prevention against Eimeria is now safer, more effective and longer-lasting.
The first vaccine against coccidiosis in poultry farming was developed in 1952.
At that time, the product contained only a single, non-attenuated species of Eimeria (Eimeria tenella). In 1974, Dr. Jeffers and his colleagues published their discovery of the precocious lines, thereby revealing the method of attenuation by precociousness.
However, for various reasons, the first vaccine containing Eimeria species attenuated by precociousness was not marketed until 1989 (Williams, 2002).
When talking about the diagnosis of Eimeria in chickens, most people think of the oocyst count (OPG) and now PCR as the gold standard methods for obtaining the most accurate diagnosis. This is partly true, however it is very important to remember that the earliest diagnosis is still only possible with the classical lesion scoring technique implemented in 1970 by Johnson & Reid. Some factors can affect the lesion scoring method and should therefore be taken into consideration: proper selection of birds, careful necropsy procedure and accurate training for lesion identification.
Most of the Eimeria vaccines available for chickens consist of live parasites that need to undergo two and sometimes three entire life cycles inside the host gut in order to trigger the immune system and subsequently establish a full protective immunity.
On the market, there are live non-attenuated and attenuated vaccines. Live non-attenuated vaccines consist of parasites that still maintain their natural virulence.
Live Eimeria vaccines have been widely used in poultry for more than 50 years now and we already described the differences among each other in a previous post (Part I). Since the 80s, attempts to develop next-generation recombinant coccidiosis vaccines have led to the identification of several candidate antigens (Blake et al. 2017). In spite of this, no recombinant Eimeria vaccine has been brought to market so far. So has anything new come to market since the 1950’s?
The reality is that nothing more than classic live Eimeria vaccines has been developed since the 1950s when the first coccidiosis vaccine reached the market. At first glance, if we think about all the other vaccines that have been brought to market in the meantime – both viral and bacterial -, and given that recombinant vaccines have been available for almost a decade now, it seems that research in the field of Eimeria vaccines has failed to keep pace.
Eimeria vaccines have been widely used in poultry since the early 1950’s and their advantages have been clearly shown. In spite of this, there are some differences between them -attenuation, composition, administration route-, but they all consist of live parasites that need to undergo two and sometimes three entire life cycles inside the host gut in order to trigger the immune system and subsequently establish full protective immunity.
There are both live non-attenuated and attenuated Eimeria vaccines on the market. Live non-attenuated vaccines consist of parasites that still maintain their natural virulence. Control of the development of adverse reactions (coccidiosis disease) is achieved by using low numbers of oocysts in vaccine preparations and in some cases even by the use of anticoccidials to control the excessive spread of vaccine strains. This strategy of “controlled exposure” allows protective immunity to develop before the contamination of litter with non-attenuated oocysts becomes severe.
The importance of information and data quality in any production process is no longer a matter for debate. Poultry production is no exception to this and we are increasingly seeing how the use of technology and relevant information is on the rise. The vaccination process and, more specifically, the control of Eimeria should form part of this new information model.
In the 2016 ‘Power of Meat’ survey, one of the emerging trends was consumers’ increasing awareness regarding traceability and transparency in the production process of the meat they consume.
There is a general consensus that consumers in the future will be more sensitive towards where their meat comes from and treatments given to animals used for meat production. For example, the same survey from 2017 stated that “antibiotic-free” was the most highly valued specific characteristic for poultry meat consumers ahead of others such as “organic” or “natural”.
A vaccine dose does not depend on body weight: the mechanism of action of vaccines is different to that of antibiotics and, as a result, the dose does not depend on the body weight of the target animal. When considering vaccines against coccidiosis in poultry, the dose is made up of a suspension of sporulated oocysts of different species of Eimeria.
In this suspension, the oocysts are not evenly distributed unless it is mixed thoroughly. If, in addition to this, the dose is reduced, the chance that the chicks will receive all the oocysts of every species decreases exponentially.
A vaccine does not have to be distributed throughout the body and the vaccine components (antigen and adjuvant) do not act directly on the pathogen. In general, the activity of vaccines starts with a rapid and local innate response depending on the route of administration.